Driver to drive?

[amdx]

On 3/20/2017 5:45 AM, tabbypurr@gmail.com wrote:

On Wednesday, 15 March 2017 01:58:40 UTC, Jim Thompson wrote:
"Procedure" tomorrow (Wednesday) at 11:00AM:

Down the throat with a scope, check out the stomach, then into the
small intestine, use side-looking ultrasound on the end of the probe
(didn't know such a thing existed) to examine the common pancreas/bile
duct, go up it with a wire, then thread a balloon up that wire,
inflate and decimate the stones, then go on up and examine the gall
bladder.

Possible later procedure, after the nauseous, tiredness, yellowness
abates, go in thru an incision and remove the gall bladder.

Such fun >:-}

If I don't show up in a day or too...

...Jim Thompson

It's 5 days now.


NT

I have checked his website a couple times, no news there.
I hope he's just waiting to so how many people love him!
Mikek

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[amdx]

On 3/20/2017 11:29 AM, dagmargoodboat@yahoo.com wrote:

On Monday, March 20, 2017 at 9:36:51 AM UTC-4, amdx wrote:
On 3/19/2017 10:56 PM, rickman wrote:
On 3/19/2017 8:20 PM, amdx wrote:
On 3/19/2017 6:42 PM, rickman wrote:
On 3/19/2017 7:31 PM, billbowden wrote:
"amdx" <nojunk@knology.net> wrote in message
newsam0ee$ch5$1@dont-email.me...
On 3/14/2017 11:18 PM, billbowden wrote:
Which is a better design. Suppose you have a 6 inch length of PVC
pipe
with
numerous turns of wire that has an inductance of say 200uH. Now
suppose
you
use the same (6 inch) piece of PVC with a ferrite rod in the core
with
considerably fewer turns of wire. Which one would capture the most
signal
at the AM Broadcast frequencies (500K to 2 Megs) and produce the
greatest
signal output? Would it be more ferrite, or more wire?


I'll run the experiment.

Do you want it tuned?

If not, I have no way to measure the signals of my local stations.
I need the resonance peaking to see the signal.

What diameter PVC?

I have 1/2" OD polystyrene that will allow a little closer coupling
between the ferrite and the wire. 400 turns #28 = 203uh air core.

I have 1/2" CPVC. actual OD. 0.615"
290 turns #28 = 200uh air core


I have 1/2 PVC, actual OD. 0.832. 175 turns #28 = 205uh air core.

Pick one.

I'll also wind one with less turns and use my best Q rod that is 8"
long x
0.375" diameter.

I will check three frequencies, 590Khz, 1290kHz and 1430Khz.

I made a post last night of the wrong experiment (6"dia not 6" long)
It has not shown up this morning, so I'll repeat my measurement
method.

To measure the signal I have a very high input impedance amp with a
gain
of 1.
I use the amp to drive a scope (ch 2) set at 50mV/div. I took the
channel
2 output from the back of the scope to drive a Boonton 92BD RF
millivolt
meter. I use the scope to compare the visual to audio from a portable
radio to know where I am tuned.
Modulation causes a bit of amplitude bounce, but I do a visual
average.

Let me know what you want.
Mikek


Actually, I'm just interested in comparing the response of two
identical
loopsticks, one using an air core and the other using a ferrite core. I
could do the experiment since there is a 50KW station about 7 miles
away and
I can see the signal from the antenna loop directly on a scope. I can
get
about 1 volt peak using a loop antenna of about 15 inches square. I
just
thought someone would know the answer without a lot of experimenting.
I have
a portable car radio with a air core loop antenna mounted on the
chassis
that measures 6.5 inch by 3/4 diameter and about 300 turns of small
wire.
Works fine and gets stations 130 miles away. But it's a power hog and
draws
100mA from a 12 volt battery. I suppose a good test would be to use a
shorter ferrite rod and fewer turns to compare the results. But I'm
lazy and
just want to know which idea is better.

Connecting a scope directly to a loop antenna may cause a loss of Q.

It does in my situation, high Q coil and very good cap. I have a high
input impedance amp with a gain of one. I drive ch 2 and get an
amplitude of 250mv pp. If I then connect a X10 scope probe to the LC
then retune for the added capacitance, I only get 70mv on ch 2. The
probe loads my LC heavily. Unloaded Q is 1200 plus or minus 200


I'm hoping not, as I am building a very high Q antenna that will
depend on a
high impedance not sapping it, but it depends on the antenna. The point
is if your measurement saps the Q, then any impact on the Q by the
ferrite will not be noticed.

If your serious, I built the Kleijer amp, 2nd version from this page.
http://www.crystal-radio.eu/fetamp/enfetamp.htm
It got a little flack from here, everyone could do better, but know one
did. Your High Q LC doesn't know it's connected.



The equations I used include Q in the formula for received signal
strength. So if the ferrite impacts the Q it won't work as well as
expected by the equations (unless you measure the Q and include that).

All ferrite has losses and usually the higher you go in frequency the
more lossy it becomes.
Here's a test I did yesterday, I put a rod in the center of a 6" dia.
coil. I reduced turns to get approx. the same inductance.

Best Ferrite Poorer ferrite
236uh 232uh 216uh
33 turn 30 turn 30 turn
Air core coil Ferrite Coil Ferrite Coil

590kHz 59 mv 43 mv 59 mv

1290kHz 15.5 mv 6.7 mv 7.1 mv

1430kHz 10.5 mv 4.2mv 3.2 mv

You can see how the ferrite causes additional losses in the upper
frequencies. If this is not understandable, let me know I'll post the
whole experiment.
Also let me know if you do decide to build a Kleijer amp, I might
save you some hassle.

It is hard to find any info on a Kleijer amp through google. I found a
thread where you were discussing building one with Fred Abse. One other
discussion by OErjan and kiwi_steve refered to usign a Kleijer amp with
links to Dick Kleijer's pages on his work.

http://www.crystal-radio.eu/fetamp/enfetamp.htm

I'm sure you've seen this. How does your amp vary much from this?

Interesting stuff. I might want to build one of these.



I posted that link above. I built mine from his schematic, and
pictures. Mine is pretty much the same except I had a pcb made.

Interesting stuff. I might want to build one of these.

PM me if you want to buy a stuffed and tested pcb. I have two left.


http://s395.photobucket.com/user/Qmavam/media/TwoPCBs.jpg.html?o=165

Here's the inside of mine.

http://s395.photobucket.com/user/Qmavam/media/inside.jpg.html?o=163

Nice. You can improve the front-end with a trivial mod by returning the
cold-end of the 20 megohm input resistor to T1's source, instead of
ground. That bootstraps (cancels) the input resistor's capacitance.

Original:
Vdd
-+-
|
T1 |--'
BF256C | 100nF
----+----->|--+--||---//
| |
[10M] |
| [470]
| |
[10M] |
| |
=== ===


Modified:
Vdd
-+-
|
T1 |--'
BF256C | 100nF
----+----->|--+--||---//
| |
[10M] |
| .-----+
| | |
[10M] | [470]
| | |
'---' ===

It's a small improvement, but it's free. If you want to get fancier
and even lower input capacitance we can bootstrap the drain, too. A
bootstrapped shield for your pass-through (where you bring the input
through your metal box) would help, too.

I have found mine very useful.
I recently put a battery pack together so I can get out in the yard
away from noise sources in the house, while testing ferrite antennas.

btw here's Kleijers home page, page to the bottom to see links to some
of his well detailed tests and experiments. Good Stuff!
http://www.crystal-radio.eu/



Mikek

Thanks for the cool measurements Mike.

Cheers,
James Arthur

Very nice on the bootstraping, I'll do that, but then I'll need to
build a second one to verify that I don't need to retune when I connect
it to the LC.

btw, my bookmark is two pages past bootstraping in "The Art of
Electronics" Third edition, by Winfield Hill, available on Amazon,
in case anyone is unaware. Thanks Win.

Mikek

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[amdx]

On 3/20/2017 11:29 AM, dagmargoodboat@yahoo.com wrote:

On Monday, March 20, 2017 at 9:36:51 AM UTC-4, amdx wrote:
On 3/19/2017 10:56 PM, rickman wrote:
On 3/19/2017 8:20 PM, amdx wrote:
On 3/19/2017 6:42 PM, rickman wrote:
On 3/19/2017 7:31 PM, billbowden wrote:
"amdx" <nojunk@knology.net> wrote in message
newsam0ee$ch5$1@dont-email.me...
On 3/14/2017 11:18 PM, billbowden wrote:
Which is a better design. Suppose you have a 6 inch length of PVC
pipe
with
numerous turns of wire that has an inductance of say 200uH. Now
suppose
you
use the same (6 inch) piece of PVC with a ferrite rod in the core
with
considerably fewer turns of wire. Which one would capture the most
signal
at the AM Broadcast frequencies (500K to 2 Megs) and produce the
greatest
signal output? Would it be more ferrite, or more wire?


I'll run the experiment.

Do you want it tuned?

If not, I have no way to measure the signals of my local stations.
I need the resonance peaking to see the signal.

What diameter PVC?

I have 1/2" OD polystyrene that will allow a little closer coupling
between the ferrite and the wire. 400 turns #28 = 203uh air core.

I have 1/2" CPVC. actual OD. 0.615"
290 turns #28 = 200uh air core


I have 1/2 PVC, actual OD. 0.832. 175 turns #28 = 205uh air core.

Pick one.

I'll also wind one with less turns and use my best Q rod that is 8"
long x
0.375" diameter.

I will check three frequencies, 590Khz, 1290kHz and 1430Khz.

I made a post last night of the wrong experiment (6"dia not 6" long)
It has not shown up this morning, so I'll repeat my measurement
method.

To measure the signal I have a very high input impedance amp with a
gain
of 1.
I use the amp to drive a scope (ch 2) set at 50mV/div. I took the
channel
2 output from the back of the scope to drive a Boonton 92BD RF
millivolt
meter. I use the scope to compare the visual to audio from a portable
radio to know where I am tuned.
Modulation causes a bit of amplitude bounce, but I do a visual
average.

Let me know what you want.
Mikek


Actually, I'm just interested in comparing the response of two
identical
loopsticks, one using an air core and the other using a ferrite core. I
could do the experiment since there is a 50KW station about 7 miles
away and
I can see the signal from the antenna loop directly on a scope. I can
get
about 1 volt peak using a loop antenna of about 15 inches square. I
just
thought someone would know the answer without a lot of experimenting.
I have
a portable car radio with a air core loop antenna mounted on the
chassis
that measures 6.5 inch by 3/4 diameter and about 300 turns of small
wire.
Works fine and gets stations 130 miles away. But it's a power hog and
draws
100mA from a 12 volt battery. I suppose a good test would be to use a
shorter ferrite rod and fewer turns to compare the results. But I'm
lazy and
just want to know which idea is better.

Connecting a scope directly to a loop antenna may cause a loss of Q.

It does in my situation, high Q coil and very good cap. I have a high
input impedance amp with a gain of one. I drive ch 2 and get an
amplitude of 250mv pp. If I then connect a X10 scope probe to the LC
then retune for the added capacitance, I only get 70mv on ch 2. The
probe loads my LC heavily. Unloaded Q is 1200 plus or minus 200


I'm hoping not, as I am building a very high Q antenna that will
depend on a
high impedance not sapping it, but it depends on the antenna. The point
is if your measurement saps the Q, then any impact on the Q by the
ferrite will not be noticed.

If your serious, I built the Kleijer amp, 2nd version from this page.
http://www.crystal-radio.eu/fetamp/enfetamp.htm
It got a little flack from here, everyone could do better, but know one
did. Your High Q LC doesn't know it's connected.



The equations I used include Q in the formula for received signal
strength. So if the ferrite impacts the Q it won't work as well as
expected by the equations (unless you measure the Q and include that).

All ferrite has losses and usually the higher you go in frequency the
more lossy it becomes.
Here's a test I did yesterday, I put a rod in the center of a 6" dia.
coil. I reduced turns to get approx. the same inductance.

Best Ferrite Poorer ferrite
236uh 232uh 216uh
33 turn 30 turn 30 turn
Air core coil Ferrite Coil Ferrite Coil

590kHz 59 mv 43 mv 59 mv

1290kHz 15.5 mv 6.7 mv 7.1 mv

1430kHz 10.5 mv 4.2mv 3.2 mv

You can see how the ferrite causes additional losses in the upper
frequencies. If this is not understandable, let me know I'll post the
whole experiment.
Also let me know if you do decide to build a Kleijer amp, I might
save you some hassle.

It is hard to find any info on a Kleijer amp through google. I found a
thread where you were discussing building one with Fred Abse. One other
discussion by OErjan and kiwi_steve refered to usign a Kleijer amp with
links to Dick Kleijer's pages on his work.

http://www.crystal-radio.eu/fetamp/enfetamp.htm

I'm sure you've seen this. How does your amp vary much from this?

Interesting stuff. I might want to build one of these.



I posted that link above. I built mine from his schematic, and
pictures. Mine is pretty much the same except I had a pcb made.

Interesting stuff. I might want to build one of these.

PM me if you want to buy a stuffed and tested pcb. I have two left.


http://s395.photobucket.com/user/Qmavam/media/TwoPCBs.jpg.html?o=165

Here's the inside of mine.

http://s395.photobucket.com/user/Qmavam/media/inside.jpg.html?o=163

Nice. You can improve the front-end with a trivial mod by returning the
cold-end of the 20 megohm input resistor to T1's source, instead of
ground. That bootstraps (cancels) the input resistor's capacitance.

Original:
Vdd
-+-
|
T1 |--'
BF256C | 100nF
----+----->|--+--||---//
| |
[10M] |
| [470]
| |
[10M] |
| |
=== ===


Modified:
Vdd
-+-
|
T1 |--'
BF256C | 100nF
----+----->|--+--||---//
| |
[10M] |
| .-----+
| | |
[10M] | [470]
| | |
'---' ===

It's a small improvement, but it's free. If you want to get fancier
and even lower input capacitance we can bootstrap the drain, too. A
bootstrapped shield for your pass-through (where you bring the input
through your metal box) would help, too.

I have found mine very useful.
I recently put a battery pack together so I can get out in the yard
away from noise sources in the house, while testing ferrite antennas.

btw here's Kleijers home page, page to the bottom to see links to some
of his well detailed tests and experiments. Good Stuff!
http://www.crystal-radio.eu/



Mikek

Thanks for the cool measurements Mike.

Cheers,
James Arthur

If you will look at my picture,
> http://s395.photobucket.com/user/Qmavam/media/inside.jpg.html?o=163
you will notice I put the 470 ohm (turquoise resistor) on the other side
of the shield, (I don't know why).
What affect would that have?

If you want to get fancier
and even lower input capacitance we can bootstrap the drain, too. A
bootstrapped shield for your pass-through (where you bring the input
through your metal box) would help, too.

OK, I'd like to get fancy, but I don't understand "A bootstrapped
shield" for my pass through.
I would like to understand physically what I need to do.

Here's another picture showing the input, there is 5/8" hole in the case
and I glued polystyrene sheet over it with the input wire coming out the
center.
> http://i395.photobucket.com/albums/pp37/Qmavam/Input.jpg
Ah, here's a picture of a previous input cap, I don't use anymore, but
it shows the input better.

http://i395.photobucket.com/albums/pp37/Qmavam/1cmx1cmspaced5mm.jpg

Mikek






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On Tuesday, March 21, 2017 at 4:07:42 AM UTC+11, k...@notreal.com wrote:

On Mon, 20 Mar 2017 01:41:14 -0400, "Michael A. Terrell"
mike.terrell@earthlink.net> wrote:

Kevin Aylward wrote:
"Kevin Aylward" wrote in message
news:kfudnRgqWLyQIlDFnZ2dnUU7-XvNnZ2d@giganews.com...

"bitrex" wrote in message news:9DdzA.62942$mb5.42260@fx19.iad...


I'm a liberal and yet, in some circumstances I do support the death
penalty.

I don't see that there can be much more of a cold-bloodied, calculated
murder, than having 12 people calmly sit on seats debating the merits
of killing someone over several days, with a state sponsored judge
exposing all sorts of "rational" arguments as to how it is ethically
justifiable to execute said person being debated. Said person is then
dragged to a room with gawking onlookers watching the deliberate
injection of chemicals to terminate said life. This is no less
barbaric than at a Roman gladiator ring where the emperor points his
thumb up or down.

What is even more grotesque, is that large numbers of those barbarians
supporting state sponsored murder are alleged Christians, despite
their role model, Jesus, emphatically instructing them that "thou
shall not kill". More, stunningly the xtians claim that it is they
that there the morally righteous ones.


It was mistranslated from, 'Thou shall not murder'. Not that you
would care.

I really think it's funny when militant atheists lecture Christians on
Christianity.

Sure is. Quite a lot of Christian thinking is absurd, and if you see it without the preconceptions installed into children brought up Christian it does often look quite amusing. Other parts are perfectly horrible, but the absurdities are a good way of waking up Christians to the defects of their belief system. Pushing the horrible bits isn't.

--
Bill Sloman, Sydney

 

[rickman]

On 3/20/2017 2:16 PM, amdx wrote:

On 3/20/2017 11:29 AM, dagmargoodboat@yahoo.com wrote:

If you will look at my picture,
http://s395.photobucket.com/user/Qmavam/media/inside.jpg.html?o=163
you will notice I put the 470 ohm (turquoise resistor) on the other side
of the shield, (I don't know why).
What affect would that have?

On Monday, March 20, 2017 at 9:36:51 AM UTC-4, amdx wrote:
If you want to get fancier
and even lower input capacitance we can bootstrap the drain, too. A
bootstrapped shield for your pass-through (where you bring the input
through your metal box) would help, too.

OK, I'd like to get fancy, but I don't understand "A bootstrapped
shield" for my pass through.
I would like to understand physically what I need to do.

I have seen this done for electrometers where the concern is leakage
current. There they call it a "guard" ring. As James says, it will
also reduce input capacitance.

I don't understand how you can bootstrap the drain though. Since it is
connected to the positive rail, I'm not even sure what that means.

Here's another picture showing the input, there is 5/8" hole in the case
and I glued polystyrene sheet over it with the input wire coming out the
center.
http://i395.photobucket.com/albums/pp37/Qmavam/Input.jpg
Ah, here's a picture of a previous input cap, I don't use anymore, but
it shows the input better.
http://i395.photobucket.com/albums/pp37/Qmavam/1cmx1cmspaced5mm.jpg

This latter image doesn't look like what is used in this image.

http://s395.photobucket.com/user/Qmavam/media/inside.jpg.html

Was this just a temporary cap in place until you got the detail work done?

--

Rick C

 

[rickman]

On 3/20/2017 3:31 PM, dagmargoodboat@yahoo.com wrote:

On Monday, March 20, 2017 at 2:16:22 PM UTC-4, amdx wrote:
On 3/20/2017 11:29 AM, dagmargoodboat@yahoo.com wrote:
On Monday, March 20, 2017 at 9:36:51 AM UTC-4, amdx wrote:
On 3/19/2017 10:56 PM, rickman wrote:
On 3/19/2017 8:20 PM, amdx wrote:
On 3/19/2017 6:42 PM, rickman wrote:
On 3/19/2017 7:31 PM, billbowden wrote:
"amdx" <nojunk@knology.net> wrote in message
newsam0ee$ch5$1@dont-email.me...
On 3/14/2017 11:18 PM, billbowden wrote:
Which is a better design. Suppose you have a 6 inch length of PVC
pipe
with
numerous turns of wire that has an inductance of say 200uH. Now
suppose
you
use the same (6 inch) piece of PVC with a ferrite rod in the core
with
considerably fewer turns of wire. Which one would capture the most
signal
at the AM Broadcast frequencies (500K to 2 Megs) and produce the
greatest
signal output? Would it be more ferrite, or more wire?


I'll run the experiment.

Do you want it tuned?

If not, I have no way to measure the signals of my local stations.
I need the resonance peaking to see the signal.

What diameter PVC?

I have 1/2" OD polystyrene that will allow a little closer coupling
between the ferrite and the wire. 400 turns #28 = 203uh air core.

I have 1/2" CPVC. actual OD. 0.615"
290 turns #28 = 200uh air core


I have 1/2 PVC, actual OD. 0.832. 175 turns #28 = 205uh air core.

Pick one.

I'll also wind one with less turns and use my best Q rod that is 8"
long x
0.375" diameter.

I will check three frequencies, 590Khz, 1290kHz and 1430Khz.

I made a post last night of the wrong experiment (6"dia not 6" long)
It has not shown up this morning, so I'll repeat my measurement
method.

To measure the signal I have a very high input impedance amp with a
gain
of 1.
I use the amp to drive a scope (ch 2) set at 50mV/div. I took the
channel
2 output from the back of the scope to drive a Boonton 92BD RF
millivolt
meter. I use the scope to compare the visual to audio from a portable
radio to know where I am tuned.
Modulation causes a bit of amplitude bounce, but I do a visual
average.

Let me know what you want.
Mikek


Actually, I'm just interested in comparing the response of two
identical
loopsticks, one using an air core and the other using a ferrite core. I
could do the experiment since there is a 50KW station about 7 miles
away and
I can see the signal from the antenna loop directly on a scope. I can
get
about 1 volt peak using a loop antenna of about 15 inches square. I
just
thought someone would know the answer without a lot of experimenting.
I have
a portable car radio with a air core loop antenna mounted on the
chassis
that measures 6.5 inch by 3/4 diameter and about 300 turns of small
wire.
Works fine and gets stations 130 miles away. But it's a power hog and
draws
100mA from a 12 volt battery. I suppose a good test would be to use a
shorter ferrite rod and fewer turns to compare the results. But I'm
lazy and
just want to know which idea is better.

Connecting a scope directly to a loop antenna may cause a loss of Q.

It does in my situation, high Q coil and very good cap. I have a high
input impedance amp with a gain of one. I drive ch 2 and get an
amplitude of 250mv pp. If I then connect a X10 scope probe to the LC
then retune for the added capacitance, I only get 70mv on ch 2. The
probe loads my LC heavily. Unloaded Q is 1200 plus or minus 200


I'm hoping not, as I am building a very high Q antenna that will
depend on a
high impedance not sapping it, but it depends on the antenna. The point
is if your measurement saps the Q, then any impact on the Q by the
ferrite will not be noticed.

If your serious, I built the Kleijer amp, 2nd version from this page.
http://www.crystal-radio.eu/fetamp/enfetamp.htm
It got a little flack from here, everyone could do better, but know one
did. Your High Q LC doesn't know it's connected.



The equations I used include Q in the formula for received signal
strength. So if the ferrite impacts the Q it won't work as well as
expected by the equations (unless you measure the Q and include that).

All ferrite has losses and usually the higher you go in frequency the
more lossy it becomes.
Here's a test I did yesterday, I put a rod in the center of a 6" dia.
coil. I reduced turns to get approx. the same inductance.

Best Ferrite Poorer ferrite
236uh 232uh 216uh
33 turn 30 turn 30 turn
Air core coil Ferrite Coil Ferrite Coil

590kHz 59 mv 43 mv 59 mv

1290kHz 15.5 mv 6.7 mv 7.1 mv

1430kHz 10.5 mv 4.2mv 3.2 mv

You can see how the ferrite causes additional losses in the upper
frequencies. If this is not understandable, let me know I'll post the
whole experiment.
Also let me know if you do decide to build a Kleijer amp, I might
save you some hassle.

It is hard to find any info on a Kleijer amp through google. I found a
thread where you were discussing building one with Fred Abse. One other
discussion by OErjan and kiwi_steve refered to usign a Kleijer amp with
links to Dick Kleijer's pages on his work.

http://www.crystal-radio.eu/fetamp/enfetamp.htm

I'm sure you've seen this. How does your amp vary much from this?

Interesting stuff. I might want to build one of these.



I posted that link above. I built mine from his schematic, and
pictures. Mine is pretty much the same except I had a pcb made.

Interesting stuff. I might want to build one of these.

PM me if you want to buy a stuffed and tested pcb. I have two left.


http://s395.photobucket.com/user/Qmavam/media/TwoPCBs.jpg.html?o=165

Here's the inside of mine.

http://s395.photobucket.com/user/Qmavam/media/inside.jpg.html?o=163

Nice. You can improve the front-end with a trivial mod by returning the
cold-end of the 20 megohm input resistor to T1's source, instead of
ground. That bootstraps (cancels) the input resistor's capacitance.

Original:
Vdd
-+-
|
T1 |--'
BF256C | 100nF
----+----->|--+--||---//
| |
[10M] |
| [470]
| |
[10M] |
| |
=== ===


Modified:
Vdd
-+-
|
T1 |--'
BF256C | 100nF
----+----->|--+--||---//
| |
[10M] |
| .-----+
| | |
[10M] | [470]
| | |
'---' ===

It's a small improvement, but it's free. If you want to get fancier
and even lower input capacitance we can bootstrap the drain, too. A
bootstrapped shield for your pass-through (where you bring the input
through your metal box) would help, too.

I have found mine very useful.
I recently put a battery pack together so I can get out in the yard
away from noise sources in the house, while testing ferrite antennas.

btw here's Kleijers home page, page to the bottom to see links to some
of his well detailed tests and experiments. Good Stuff!
http://www.crystal-radio.eu/



Mikek

Thanks for the cool measurements Mike.

Cheers,
James Arthur


If you will look at my picture,
http://s395.photobucket.com/user/Qmavam/media/inside.jpg.html?o=163
you will notice I put the 470 ohm (turquoise resistor) on the other side
of the shield, (I don't know why).
What affect would that have?

If you want to get fancier
and even lower input capacitance we can bootstrap the drain, too. A
bootstrapped shield for your pass-through (where you bring the input
through your metal box) would help, too.

OK, I'd like to get fancy, but I don't understand "A bootstrapped
shield" for my pass through.
I would like to understand physically what I need to do.

The idea is to shield your signal with coax, then to drive the coax's
shield to reduce the effect of the coax's capacitance.

In this case it was because I thought you were using a high-capacitance
(for the situation) signal feed-through, but it looks like you've
already done a very nice job providing low capacitance.

Here's another picture showing the input, there is 5/8" hole in the case
and I glued polystyrene sheet over it with the input wire coming out the
center.
http://i395.photobucket.com/albums/pp37/Qmavam/Input.jpg
Ah, here's a picture of a previous input cap, I don't use anymore, but
it shows the input better.
http://i395.photobucket.com/albums/pp37/Qmavam/1cmx1cmspaced5mm.jpg

The idea of bootstrapping is to provide a unity-gain buffer, then make
all the circuit nodes swing with the input voltage, so that the input
signal doesn't have to charge any of the nodes' capacitances.

This illustrates the ideas--

+12V +12V
-+- -+-
| |
| [22k] R4
\| |
Q1 |---+----------.
.<| | |
| [47k] R5 |
(shield) T1 |--' | |
------ BF256C | === |
----------+----->|--+----------------|---//
---+-- | | Vdd |
| [10M] R1 | -+- |
| | | | |
| [10M] R2 | |/ Q2 |
| | .-----+---| |
| | | | |>. C1 |
| '---' R3[470] | 100n |
| | +---+--||--'
| === |R6 |
| [1K] '--||--.
| | 100n |
| === C2 |
'---------------------------------+
|
[22k] R7
|
===

Q1 forces the drain to move up and down *with* the input signal,
cancelling Cgd. T1's source already follows the input signal,
reducing the effective Cgs.

I've shown Q2 driving a shield. It's optional--you likely don't need that.

If our buffer (Q2) and T1 together manage a gain of 0.8, we'll cancel
roughly 80% of the input capacitance. (A more complicated buffer
getting closer to unity gain would provide even better input
capacitance cancellation.)

Your author says his 0.3pF input cap and FET buffer form a 1:17 divider,
implying T1's effective input capacitance is about 5pF. You should be
able to improve that by a factor of five without breaking a sweat, by a
factor of ten with a little more care.

Ok, I get it now. So the BF256C ends up being operated with a constant
voltage across the D-S? Essentially all three terminals run at the same
AC voltage.

Is there any reason to limit the input resistors to 20 Meg? From what
I've seen on Kleijer's web site 20 Meg would be significant. But I am
forgetting about the bootstrap. That also bootstraps the resistance
making it *much* higher, yes?

Why use the BF256C as opposed to any other part? What characteristic
makes it a good choice over other devices?

--

Rick C

 

On Monday, March 20, 2017 at 4:46:32 PM UTC-4, rickman wrote:

On 3/20/2017 3:31 PM, dagmargoodboat@yahoo.com wrote:
On Monday, March 20, 2017 at 2:16:22 PM UTC-4, amdx wrote:
On 3/20/2017 11:29 AM, dagmargoodboat@yahoo.com wrote:

If you want to get fancier
and even lower input capacitance we can bootstrap the drain, too. A
bootstrapped shield for your pass-through (where you bring the input
through your metal box) would help, too.

OK, I'd like to get fancy, but I don't understand "A bootstrapped
shield" for my pass through.
I would like to understand physically what I need to do.

The idea is to shield your signal with coax, then to drive the coax's
shield to reduce the effect of the coax's capacitance.

In this case it was because I thought you were using a high-capacitance
(for the situation) signal feed-through, but it looks like you've
already done a very nice job providing low capacitance.

Here's another picture showing the input, there is 5/8" hole in the case
and I glued polystyrene sheet over it with the input wire coming out the
center.
http://i395.photobucket.com/albums/pp37/Qmavam/Input.jpg
Ah, here's a picture of a previous input cap, I don't use anymore, but
it shows the input better.
http://i395.photobucket.com/albums/pp37/Qmavam/1cmx1cmspaced5mm.jpg

The idea of bootstrapping is to provide a unity-gain buffer, then make
all the circuit nodes swing with the input voltage, so that the input
signal doesn't have to charge any of the nodes' capacitances.

This illustrates the ideas--

+12V +12V
-+- -+-
| |
| [22k] R4
\| |
Q1 |---+----------.
.<| | |
| [47k] R5 |
(shield) T1 |--' | |
------ BF256C | === |
----------+----->|--+----------------|---//
---+-- | | Vdd |
| [10M] R1 | -+- |
| | | | |
| [10M] R2 | |/ Q2 |
| | .-----+---| |
| | | | |>. C1 |
| '---' R3[470] | 100n |
| | +---+--||--'
| === |R6 |
| [1K] '--||--.
| | 100n |
| === C2 |
'---------------------------------+
|
[22k] R7
|
===

Q1 forces the drain to move up and down *with* the input signal,
cancelling Cgd. T1's source already follows the input signal,
reducing the effective Cgs.

I've shown Q2 driving a shield. It's optional--you likely don't need that.

If our buffer (Q2) and T1 together manage a gain of 0.8, we'll cancel
roughly 80% of the input capacitance. (A more complicated buffer
getting closer to unity gain would provide even better input
capacitance cancellation.)

Your author says his 0.3pF input cap and FET buffer form a 1:17 divider,
implying T1's effective input capacitance is about 5pF. You should be
able to improve that by a factor of five without breaking a sweat, by a
factor of ten with a little more care.

Ok, I get it now. So the BF256C ends up being operated with a constant
voltage across the D-S? Essentially all three terminals run at the same
AC voltage.

Right.

Is there any reason to limit the input resistors to 20 Meg? From what
I've seen on Kleijer's web site 20 Meg would be significant.

Could be higher I guess. Depends on the FET's Ig. I was just piling onto
the existing circuit.

But I am
forgetting about the bootstrap. That also bootstraps the resistance
making it *much* higher, yes?

Raises the input impedance, yes. Much? Maybe 5x for this quickie mod.

Why use the BF256C as opposed to any other part? What characteristic
makes it a good choice over other devices?

I didn't pick it, but I'm sure the designer picked that FET for low
input capacitance and low feedback capacitance.

He chose well. I might consider a 2n4117, though, depending on the
bandwidth requirements (I don't know how fast this thing has to be).
But Mike already has the BF256C on hand, and it's pretty good.

Cheers,
James Arthur

 

On Monday, March 20, 2017 at 6:15:37 PM UTC-4, amdx wrote:

On 3/20/2017 2:31 PM, dagmargoodboat@yahoo.com wrote:

The idea of bootstrapping is to provide a unity-gain buffer, then make
all the circuit nodes swing with the input voltage, so that the input
signal doesn't have to charge any of the nodes' capacitances.

This illustrates the ideas--

+12V +12V
-+- -+-
| |
| [22k] R4
\| |
Q1 |---+----------.
.<| | |
| [47k] R5 |
(shield) T1 |--' | |
------ BF256C | === |
----------+----->|--+----------------|---//
---+-- | | Vdd |
| [10M] R1 | -+- |
| | | | |
| [10M] R2 | |/ Q2 |
| | .-----+---| |
| | | | |>. C1 |
| '---' R3[470] | 100n |
| | +---+--||--'
| === |R6 |
| [1K] '--||--.
| | 100n |
| === C2 |
'---------------------------------+
|
[22k] R7
|
===

Q1 forces the drain to move up and down *with* the input signal,
cancelling Cgd. T1's source already follows the input signal,
reducing the effective Cgs.

I've shown Q2 driving a shield. It's optional--you likely don't need that.

Ok, so if I was using short coax to connect to my LC, Q2 would drive
the shield to null it's capacitance.

Yep.

I now use two 6" wires to clip to the LC. the two wire run about 2"
apart. I have wondered how much capacitance the leads add.

I suspect a lot. But you could always measure & be sure.

For a permanent test fixture with a tuning cap and a signal strength
meter, ready to plunk any coil into for testing this would be great use
of a fixed coax input.

Yes.

If our buffer (Q2) and T1 together manage a gain of 0.8, we'll cancel
roughly 80% of the input capacitance. (A more complicated buffer
getting closer to unity gain would provide even better input
capacitance cancellation.)

Still talking a about coax capacitance? Right

No, this applies to the whole scheme. The more closely all the nodes
follow the input signal voltage, the better our result.

Your author says his 0.3pF input cap and FET buffer form a 1:17 divider,
implying T1's effective input capacitance is about 5pF. You should be
able to improve that by a factor of five without breaking a sweat, by a
factor of ten with a little more care.

Now is that from the 20meg moving to the T1 source, or some more from
Q1 or both?

Both.

> Note I added the missing 0.3pf cap to the schematic.

Yes. I was just sketching the relevant part of the front-end.

Can I tell this is working if my 1X gain increases?
The 17 to 1 divider of the input cap and the gate capacitance and the 17
times gain of the amplifier equals 1X.

Say I get 80% T1 gate cancellation (by moving the 20Meg), now we have
effectively 1pf.
1pf/0.3pf = 3.33 and the amp gain 17 / 3.33 = 5.1
So I would think my total circuit gain would increase to 5.1.
Or do I not get it?

You've got it perfectly. I don't expect a very large improvement from
bootstrapping the 20M alone though--a resistor's capacitance is pretty
low already, and two in series, even lower.

Your author's figures are inconsistent. He starts saying the input
capacitance is 1.4pF and the input coupling cap is 0.3pF, but then he
says the 0.3pF and FET T1's capacitances form a 17:1 divider. That can't
all be true--0.3pF should form a 5.7:1 divider with a 1.4pF input, not
17:1.

When I guesstimate a 5x improvement, I'm banking on the 17:1 being true,
c.in(eff) being 5pF, and getting that down to 1pF, roughly, with the
circuit I sketched.

If you're already really at 1.4pF the improvement will only be 1.0pF/1.4pF,
and not 1.0pF/5pF.

As I said before, a better buffer could do better--you could tweak the
bootstrap to perfect null--but then chances are you'd have an oscillator.

What I posted seemed like a reasonable compromise for a first try.

+12V +12V
-+- -+-
I added 0.3pf cap | |
| | [22k] R4
| \| |
| Q1 |---+----------.
\|/ .<| | |
| | [47k] R5 |
(shield) | T1 |--' | |
------\|/ BF256C | === |
-------||-+----->|--+----------------|---//
------ | | Vdd |
| [10M] R1 | -+- |
| | | | |
| [10M] R2 | |/ Q2 |
| | .-----+---| |
| | | | |>. C1 |
| '---' R3[470] | 100n |
| | +---+--||--'
| === |R6 |
| [1K] '--||--.
| | 100n |
| === C2 |
'---------------------------------+
|
[22k] R7
|
===

Cheers,
James Arthur

 

[amdx]

On 3/20/2017 2:31 PM, dagmargoodboat@yahoo.com wrote:

On Monday, March 20, 2017 at 2:16:22 PM UTC-4, amdx wrote:
On 3/20/2017 11:29 AM, dagmargoodboat@yahoo.com wrote:
On Monday, March 20, 2017 at 9:36:51 AM UTC-4, amdx wrote:
On 3/19/2017 10:56 PM, rickman wrote:
On 3/19/2017 8:20 PM, amdx wrote:
On 3/19/2017 6:42 PM, rickman wrote:
On 3/19/2017 7:31 PM, billbowden wrote:
"amdx" <nojunk@knology.net> wrote in message
newsam0ee$ch5$1@dont-email.me...
On 3/14/2017 11:18 PM, billbowden wrote:
Which is a better design. Suppose you have a 6 inch length of PVC
pipe
with
numerous turns of wire that has an inductance of say 200uH. Now
suppose
you
use the same (6 inch) piece of PVC with a ferrite rod in the core
with
considerably fewer turns of wire. Which one would capture the most
signal
at the AM Broadcast frequencies (500K to 2 Megs) and produce the
greatest
signal output? Would it be more ferrite, or more wire?


I'll run the experiment.

Do you want it tuned?

If not, I have no way to measure the signals of my local stations.
I need the resonance peaking to see the signal.

What diameter PVC?

I have 1/2" OD polystyrene that will allow a little closer coupling
between the ferrite and the wire. 400 turns #28 = 203uh air core.

I have 1/2" CPVC. actual OD. 0.615"
290 turns #28 = 200uh air core


I have 1/2 PVC, actual OD. 0.832. 175 turns #28 = 205uh air core.

Pick one.

I'll also wind one with less turns and use my best Q rod that is 8"
long x
0.375" diameter.

I will check three frequencies, 590Khz, 1290kHz and 1430Khz.

I made a post last night of the wrong experiment (6"dia not 6" long)
It has not shown up this morning, so I'll repeat my measurement
method.

To measure the signal I have a very high input impedance amp with a
gain
of 1.
I use the amp to drive a scope (ch 2) set at 50mV/div. I took the
channel
2 output from the back of the scope to drive a Boonton 92BD RF
millivolt
meter. I use the scope to compare the visual to audio from a portable
radio to know where I am tuned.
Modulation causes a bit of amplitude bounce, but I do a visual
average.

Let me know what you want.
Mikek


Actually, I'm just interested in comparing the response of two
identical
loopsticks, one using an air core and the other using a ferrite core. I
could do the experiment since there is a 50KW station about 7 miles
away and
I can see the signal from the antenna loop directly on a scope. I can
get
about 1 volt peak using a loop antenna of about 15 inches square. I
just
thought someone would know the answer without a lot of experimenting.
I have
a portable car radio with a air core loop antenna mounted on the
chassis
that measures 6.5 inch by 3/4 diameter and about 300 turns of small
wire.
Works fine and gets stations 130 miles away. But it's a power hog and
draws
100mA from a 12 volt battery. I suppose a good test would be to use a
shorter ferrite rod and fewer turns to compare the results. But I'm
lazy and
just want to know which idea is better.

Connecting a scope directly to a loop antenna may cause a loss of Q.

It does in my situation, high Q coil and very good cap. I have a high
input impedance amp with a gain of one. I drive ch 2 and get an
amplitude of 250mv pp. If I then connect a X10 scope probe to the LC
then retune for the added capacitance, I only get 70mv on ch 2. The
probe loads my LC heavily. Unloaded Q is 1200 plus or minus 200


I'm hoping not, as I am building a very high Q antenna that will
depend on a
high impedance not sapping it, but it depends on the antenna. The point
is if your measurement saps the Q, then any impact on the Q by the
ferrite will not be noticed.

If your serious, I built the Kleijer amp, 2nd version from this page.
http://www.crystal-radio.eu/fetamp/enfetamp.htm
It got a little flack from here, everyone could do better, but know one
did. Your High Q LC doesn't know it's connected.



The equations I used include Q in the formula for received signal
strength. So if the ferrite impacts the Q it won't work as well as
expected by the equations (unless you measure the Q and include that).

All ferrite has losses and usually the higher you go in frequency the
more lossy it becomes.
Here's a test I did yesterday, I put a rod in the center of a 6" dia.
coil. I reduced turns to get approx. the same inductance.

Best Ferrite Poorer ferrite
236uh 232uh 216uh
33 turn 30 turn 30 turn
Air core coil Ferrite Coil Ferrite Coil

590kHz 59 mv 43 mv 59 mv

1290kHz 15.5 mv 6.7 mv 7.1 mv

1430kHz 10.5 mv 4.2mv 3.2 mv

You can see how the ferrite causes additional losses in the upper
frequencies. If this is not understandable, let me know I'll post the
whole experiment.
Also let me know if you do decide to build a Kleijer amp, I might
save you some hassle.

It is hard to find any info on a Kleijer amp through google. I found a
thread where you were discussing building one with Fred Abse. One other
discussion by OErjan and kiwi_steve refered to usign a Kleijer amp with
links to Dick Kleijer's pages on his work.

http://www.crystal-radio.eu/fetamp/enfetamp.htm

I'm sure you've seen this. How does your amp vary much from this?

Interesting stuff. I might want to build one of these.



I posted that link above. I built mine from his schematic, and
pictures. Mine is pretty much the same except I had a pcb made.

Interesting stuff. I might want to build one of these.

PM me if you want to buy a stuffed and tested pcb. I have two left.


http://s395.photobucket.com/user/Qmavam/media/TwoPCBs.jpg.html?o=165

Here's the inside of mine.

http://s395.photobucket.com/user/Qmavam/media/inside.jpg.html?o=163

Nice. You can improve the front-end with a trivial mod by returning the
cold-end of the 20 megohm input resistor to T1's source, instead of
ground. That bootstraps (cancels) the input resistor's capacitance.

Original:
Vdd
-+-
|
T1 |--'
BF256C | 100nF
----+----->|--+--||---//
| |
[10M] |
| [470]
| |
[10M] |
| |
=== ===


Modified:
Vdd
-+-
|
T1 |--'
BF256C | 100nF
----+----->|--+--||---//
| |
[10M] |
| .-----+
| | |
[10M] | [470]
| | |
'---' ===

It's a small improvement, but it's free. If you want to get fancier
and even lower input capacitance we can bootstrap the drain, too. A
bootstrapped shield for your pass-through (where you bring the input
through your metal box) would help, too.

I have found mine very useful.
I recently put a battery pack together so I can get out in the yard
away from noise sources in the house, while testing ferrite antennas.

btw here's Kleijers home page, page to the bottom to see links to some
of his well detailed tests and experiments. Good Stuff!
http://www.crystal-radio.eu/



Mikek

Thanks for the cool measurements Mike.

Cheers,
James Arthur


If you will look at my picture,
http://s395.photobucket.com/user/Qmavam/media/inside.jpg.html?o=163
you will notice I put the 470 ohm (turquoise resistor) on the other side
of the shield, (I don't know why).
What affect would that have?

If you want to get fancier
and even lower input capacitance we can bootstrap the drain, too. A
bootstrapped shield for your pass-through (where you bring the input
through your metal box) would help, too.

OK, I'd like to get fancy, but I don't understand "A bootstrapped
shield" for my pass through.
I would like to understand physically what I need to do.

The idea is to shield your signal with coax, then to drive the coax's
shield to reduce the effect of the coax's capacitance.

In this case it was because I thought you were using a high-capacitance
(for the situation) signal feed-through, but it looks like you've
already done a very nice job providing low capacitance.

Here's another picture showing the input, there is 5/8" hole in the case
and I glued polystyrene sheet over it with the input wire coming out the
center.
http://i395.photobucket.com/albums/pp37/Qmavam/Input.jpg
Ah, here's a picture of a previous input cap, I don't use anymore, but
it shows the input better.
http://i395.photobucket.com/albums/pp37/Qmavam/1cmx1cmspaced5mm.jpg

The idea of bootstrapping is to provide a unity-gain buffer, then make
all the circuit nodes swing with the input voltage, so that the input
signal doesn't have to charge any of the nodes' capacitances.

This illustrates the ideas--

+12V +12V
-+- -+-
| |
| [22k] R4
\| |
Q1 |---+----------.
.<| | |
| [47k] R5 |
(shield) T1 |--' | |
------ BF256C | === |
----------+----->|--+----------------|---//
---+-- | | Vdd |
| [10M] R1 | -+- |
| | | | |
| [10M] R2 | |/ Q2 |
| | .-----+---| |
| | | | |>. C1 |
| '---' R3[470] | 100n |
| | +---+--||--'
| === |R6 |
| [1K] '--||--.
| | 100n |
| === C2 |
'---------------------------------+
|
[22k] R7
|
===

Q1 forces the drain to move up and down *with* the input signal,
cancelling Cgd. T1's source already follows the input signal,
reducing the effective Cgs.

I've shown Q2 driving a shield. It's optional--you likely don't need that.

Ok, so if I was using short coax to connect to my LC, Q2 would drive
the shield to null it's capacitance.

I now use two 6" wires to clip to the LC. the two wire run about 2"
apart. I have wondered how much capacitance the leads add.
For a permanent test fixture with a tuning cap and a signal strength
meter, ready to plunk any coil into for testing this would be great use
of a fixed coax input.

If our buffer (Q2) and T1 together manage a gain of 0.8, we'll cancel
roughly 80% of the input capacitance. (A more complicated buffer
getting closer to unity gain would provide even better input
capacitance cancellation.)

Still talking a about coax capacitance? Right

Your author says his 0.3pF input cap and FET buffer form a 1:17 divider,
implying T1's effective input capacitance is about 5pF. You should be
able to improve that by a factor of five without breaking a sweat, by a
factor of ten with a little more care.

Now is that from the 20meg moving to the T1 source, or some more from
Q1 or both?

Note I added the missing 0.3pf cap to the schematic.

Can I tell this is working if my 1X gain increases?
The 17 to 1 divider of the input cap and the gate capacitance and the 17
times gain of the amplifier equals 1X.

Say I get 80% T1 gate cancellation (by moving the 20Meg), now we have
effectively 1pf.
1pf/0.3pf = 3.33 and the amp gain 17 / 3.33 = 5.1
So I would think my total circuit gain would increase to 5.1.
Or do I not get it?
Mikek

+12V +12V
-+- -+-
I added 0.3pf cap | |
| | [22k] R4
| \| |
| Q1 |---+----------.
\|/ .<| | |
| | [47k] R5 |
(shield) | T1 |--' | |
------\|/ BF256C | === |
-------||-+----->|--+----------------|---//
------ | | Vdd |
| [10M] R1 | -+- |
| | | | |
| [10M] R2 | |/ Q2 |
| | .-----+---| |
| | | | |>. C1 |
| '---' R3[470] | 100n |
| | +---+--||--'
| === |R6 |
| [1K] '--||--.
| | 100n |
| === C2 |
'---------------------------------+
|
[22k] R7
|
===


Cheers,
James Arthur

---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

 

[amdx]

On 3/20/2017 3:46 PM, rickman wrote:

On 3/20/2017 3:31 PM, dagmargoodboat@yahoo.com wrote:
On Monday, March 20, 2017 at 2:16:22 PM UTC-4, amdx wrote:
On 3/20/2017 11:29 AM, dagmargoodboat@yahoo.com wrote:
On Monday, March 20, 2017 at 9:36:51 AM UTC-4, amdx wrote:
On 3/19/2017 10:56 PM, rickman wrote:
On 3/19/2017 8:20 PM, amdx wrote:
On 3/19/2017 6:42 PM, rickman wrote:
On 3/19/2017 7:31 PM, billbowden wrote:
"amdx" <nojunk@knology.net> wrote in message
newsam0ee$ch5$1@dont-email.me...
On 3/14/2017 11:18 PM, billbowden wrote:
Which is a better design. Suppose you have a 6 inch length of
PVC
pipe
with
numerous turns of wire that has an inductance of say 200uH. Now
suppose
you
use the same (6 inch) piece of PVC with a ferrite rod in the
core
with
considerably fewer turns of wire. Which one would capture
the most
signal
at the AM Broadcast frequencies (500K to 2 Megs) and produce the
greatest
signal output? Would it be more ferrite, or more wire?


I'll run the experiment.

Do you want it tuned?

If not, I have no way to measure the signals of my local
stations.
I need the resonance peaking to see the signal.

What diameter PVC?

I have 1/2" OD polystyrene that will allow a little closer
coupling
between the ferrite and the wire. 400 turns #28 = 203uh air core.

I have 1/2" CPVC. actual OD. 0.615"
290 turns #28 = 200uh air core


I have 1/2 PVC, actual OD. 0.832. 175 turns #28 = 205uh air core.

Pick one.

I'll also wind one with less turns and use my best Q rod that
is 8"
long x
0.375" diameter.

I will check three frequencies, 590Khz, 1290kHz and 1430Khz.

I made a post last night of the wrong experiment (6"dia not
6" long)
It has not shown up this morning, so I'll repeat my measurement
method.

To measure the signal I have a very high input impedance amp
with a
gain
of 1.
I use the amp to drive a scope (ch 2) set at 50mV/div. I took the
channel
2 output from the back of the scope to drive a Boonton 92BD RF
millivolt
meter. I use the scope to compare the visual to audio from a
portable
radio to know where I am tuned.
Modulation causes a bit of amplitude bounce, but I do a visual
average.

Let me know what you want.
Mikek


Actually, I'm just interested in comparing the response of two
identical
loopsticks, one using an air core and the other using a ferrite
core. I
could do the experiment since there is a 50KW station about 7
miles
away and
I can see the signal from the antenna loop directly on a scope.
I can
get
about 1 volt peak using a loop antenna of about 15 inches
square. I
just
thought someone would know the answer without a lot of
experimenting.
I have
a portable car radio with a air core loop antenna mounted on the
chassis
that measures 6.5 inch by 3/4 diameter and about 300 turns of
small
wire.
Works fine and gets stations 130 miles away. But it's a power
hog and
draws
100mA from a 12 volt battery. I suppose a good test would be to
use a
shorter ferrite rod and fewer turns to compare the results. But
I'm
lazy and
just want to know which idea is better.

Connecting a scope directly to a loop antenna may cause a loss
of Q.

It does in my situation, high Q coil and very good cap. I have a
high
input impedance amp with a gain of one. I drive ch 2 and get an
amplitude of 250mv pp. If I then connect a X10 scope probe to the LC
then retune for the added capacitance, I only get 70mv on ch 2. The
probe loads my LC heavily. Unloaded Q is 1200 plus or minus 200


I'm hoping not, as I am building a very high Q antenna that will
depend on a
high impedance not sapping it, but it depends on the antenna.
The point
is if your measurement saps the Q, then any impact on the Q by the
ferrite will not be noticed.

If your serious, I built the Kleijer amp, 2nd version from this
page.
http://www.crystal-radio.eu/fetamp/enfetamp.htm
It got a little flack from here, everyone could do better, but
know one
did. Your High Q LC doesn't know it's connected.



The equations I used include Q in the formula for received signal
strength. So if the ferrite impacts the Q it won't work as well as
expected by the equations (unless you measure the Q and include
that).

All ferrite has losses and usually the higher you go in
frequency the
more lossy it becomes.
Here's a test I did yesterday, I put a rod in the center of a 6"
dia.
coil. I reduced turns to get approx. the same inductance.

Best Ferrite Poorer ferrite
236uh 232uh 216uh
33 turn 30 turn 30 turn
Air core coil Ferrite Coil Ferrite Coil

590kHz 59 mv 43 mv 59 mv

1290kHz 15.5 mv 6.7 mv 7.1 mv

1430kHz 10.5 mv 4.2mv 3.2 mv

You can see how the ferrite causes additional losses in the upper
frequencies. If this is not understandable, let me know I'll post
the
whole experiment.
Also let me know if you do decide to build a Kleijer amp, I might
save you some hassle.

It is hard to find any info on a Kleijer amp through google. I
found a
thread where you were discussing building one with Fred Abse. One
other
discussion by OErjan and kiwi_steve refered to usign a Kleijer amp
with
links to Dick Kleijer's pages on his work.

http://www.crystal-radio.eu/fetamp/enfetamp.htm

I'm sure you've seen this. How does your amp vary much from this?

Interesting stuff. I might want to build one of these.



I posted that link above. I built mine from his schematic, and
pictures. Mine is pretty much the same except I had a pcb made.

Interesting stuff. I might want to build one of these.

PM me if you want to buy a stuffed and tested pcb. I have two left.


http://s395.photobucket.com/user/Qmavam/media/TwoPCBs.jpg.html?o=165

Here's the inside of mine.

http://s395.photobucket.com/user/Qmavam/media/inside.jpg.html?o=163

Nice. You can improve the front-end with a trivial mod by returning
the
cold-end of the 20 megohm input resistor to T1's source, instead of
ground. That bootstraps (cancels) the input resistor's capacitance.

Original:
Vdd
-+-
|
T1 |--'
BF256C | 100nF
----+----->|--+--||---//
| |
[10M] |
| [470]
| |
[10M] |
| |
=== ===


Modified:
Vdd
-+-
|
T1 |--'
BF256C | 100nF
----+----->|--+--||---//
| |
[10M] |
| .-----+
| | |
[10M] | [470]
| | |
'---' ===

It's a small improvement, but it's free. If you want to get fancier
and even lower input capacitance we can bootstrap the drain, too. A
bootstrapped shield for your pass-through (where you bring the input
through your metal box) would help, too.

I have found mine very useful.
I recently put a battery pack together so I can get out in the yard
away from noise sources in the house, while testing ferrite antennas.

btw here's Kleijers home page, page to the bottom to see links to some
of his well detailed tests and experiments. Good Stuff!
http://www.crystal-radio.eu/



Mikek

Thanks for the cool measurements Mike.

Cheers,
James Arthur


If you will look at my picture,
http://s395.photobucket.com/user/Qmavam/media/inside.jpg.html?o=163
you will notice I put the 470 ohm (turquoise resistor) on the other side
of the shield, (I don't know why).
What affect would that have?

If you want to get fancier
and even lower input capacitance we can bootstrap the drain, too. A
bootstrapped shield for your pass-through (where you bring the input
through your metal box) would help, too.

OK, I'd like to get fancy, but I don't understand "A bootstrapped
shield" for my pass through.
I would like to understand physically what I need to do.

The idea is to shield your signal with coax, then to drive the coax's
shield to reduce the effect of the coax's capacitance.

In this case it was because I thought you were using a high-capacitance
(for the situation) signal feed-through, but it looks like you've
already done a very nice job providing low capacitance.

Here's another picture showing the input, there is 5/8" hole in the case
and I glued polystyrene sheet over it with the input wire coming out the
center.
http://i395.photobucket.com/albums/pp37/Qmavam/Input.jpg
Ah, here's a picture of a previous input cap, I don't use anymore, but
it shows the input better.
http://i395.photobucket.com/albums/pp37/Qmavam/1cmx1cmspaced5mm.jpg

The idea of bootstrapping is to provide a unity-gain buffer, then make
all the circuit nodes swing with the input voltage, so that the input
signal doesn't have to charge any of the nodes' capacitances.

This illustrates the ideas--

+12V +12V
-+- -+-
| |
| [22k] R4
\| |
Q1 |---+----------.
.<| | |
| [47k] R5 |
(shield) T1 |--' | |
------ BF256C | === |
----------+----->|--+----------------|---//
---+-- | | Vdd |
| [10M] R1 | -+- |
| | | | |
| [10M] R2 | |/ Q2 |
| | .-----+---| |
| | | | |>. C1 |
| '---' R3[470] | 100n |
| | +---+--||--'
| === |R6 |
| [1K] '--||--.
| | 100n |
| === C2 |
'---------------------------------+
|
[22k] R7
|
===

Q1 forces the drain to move up and down *with* the input signal,
cancelling Cgd. T1's source already follows the input signal,
reducing the effective Cgs.

I've shown Q2 driving a shield. It's optional--you likely don't need
that.

If our buffer (Q2) and T1 together manage a gain of 0.8, we'll cancel
roughly 80% of the input capacitance. (A more complicated buffer
getting closer to unity gain would provide even better input
capacitance cancellation.)

Your author says his 0.3pF input cap and FET buffer form a 1:17 divider,
implying T1's effective input capacitance is about 5pF. You should be
able to improve that by a factor of five without breaking a sweat, by a
factor of ten with a little more care.

Ok, I get it now. So the BF256C ends up being operated with a constant
voltage across the D-S? Essentially all three terminals run at the same
AC voltage.

Is there any reason to limit the input resistors to 20 Meg? From what
I've seen on Kleijer's web site 20 Meg would be significant. But I am
forgetting about the bootstrap. That also bootstraps the resistance
making it *much* higher, yes?

Why use the BF256C as opposed to any other part? What characteristic
makes it a good choice over other devices?

I tried the surface mount BFR92A recommended and could not get it to
stop oscillating.
Mikek

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[amdx]

On 3/20/2017 3:34 PM, rickman wrote:

On 3/20/2017 2:16 PM, amdx wrote:
On 3/20/2017 11:29 AM, dagmargoodboat@yahoo.com wrote:

If you will look at my picture,
http://s395.photobucket.com/user/Qmavam/media/inside.jpg.html?o=163
you will notice I put the 470 ohm (turquoise resistor) on the other side
of the shield, (I don't know why).
What affect would that have?

On Monday, March 20, 2017 at 9:36:51 AM UTC-4, amdx wrote:
If you want to get fancier
and even lower input capacitance we can bootstrap the drain, too. A
bootstrapped shield for your pass-through (where you bring the input
through your metal box) would help, too.

OK, I'd like to get fancy, but I don't understand "A bootstrapped
shield" for my pass through.
I would like to understand physically what I need to do.

I have seen this done for electrometers where the concern is leakage
current. There they call it a "guard" ring. As James says, it will
also reduce input capacitance.

I don't understand how you can bootstrap the drain though. Since it is
connected to the positive rail, I'm not even sure what that means.


Here's another picture showing the input, there is 5/8" hole in the case
and I glued polystyrene sheet over it with the input wire coming out the
center.
http://i395.photobucket.com/albums/pp37/Qmavam/Input.jpg
Ah, here's a picture of a previous input cap, I don't use anymore, but
it shows the input better.
http://i395.photobucket.com/albums/pp37/Qmavam/1cmx1cmspaced5mm.jpg

This latter image doesn't look like what is used in this image.

http://s395.photobucket.com/user/Qmavam/media/inside.jpg.html

Was this just a temporary cap in place until you got the detail work done?

Yes, that was a first iteration, nothing wrong with it, but it wasn't
as stable (two wires with a weights on the end) as my tiny piece of
double sided pcb.
Mikek

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[rickman]

On 3/20/2017 6:15 PM, amdx wrote:

On 3/20/2017 2:31 PM, dagmargoodboat@yahoo.com wrote:

The idea is to shield your signal with coax, then to drive the coax's
shield to reduce the effect of the coax's capacitance.

In this case it was because I thought you were using a high-capacitance
(for the situation) signal feed-through, but it looks like you've
already done a very nice job providing low capacitance.

Here's another picture showing the input, there is 5/8" hole in the case
and I glued polystyrene sheet over it with the input wire coming out the
center.
http://i395.photobucket.com/albums/pp37/Qmavam/Input.jpg
Ah, here's a picture of a previous input cap, I don't use anymore, but
it shows the input better.
http://i395.photobucket.com/albums/pp37/Qmavam/1cmx1cmspaced5mm.jpg

The idea of bootstrapping is to provide a unity-gain buffer, then make
all the circuit nodes swing with the input voltage, so that the input
signal doesn't have to charge any of the nodes' capacitances.

This illustrates the ideas--

+12V +12V
-+- -+-
| |
| [22k] R4
\| |
Q1 |---+----------.
.<| | |
| [47k] R5 |
(shield) T1 |--' | |
------ BF256C | === |
----------+----->|--+----------------|---//
---+-- | | Vdd |
| [10M] R1 | -+- |
| | | | |
| [10M] R2 | |/ Q2 |
| | .-----+---| |
| | | | |>. C1 |
| '---' R3[470] | 100n |
| | +---+--||--'
| === |R6 |
| [1K] '--||--.
| | 100n |
| === C2 |
'---------------------------------+
|
[22k] R7
|
===

Q1 forces the drain to move up and down *with* the input signal,
cancelling Cgd. T1's source already follows the input signal,
reducing the effective Cgs.

I've shown Q2 driving a shield. It's optional--you likely don't need
that.

Ok, so if I was using short coax to connect to my LC, Q2 would drive
the shield to null it's capacitance.

I now use two 6" wires to clip to the LC. the two wire run about 2"
apart. I have wondered how much capacitance the leads add.
For a permanent test fixture with a tuning cap and a signal strength
meter, ready to plunk any coil into for testing this would be great use
of a fixed coax input.


If our buffer (Q2) and T1 together manage a gain of 0.8, we'll cancel
roughly 80% of the input capacitance. (A more complicated buffer
getting closer to unity gain would provide even better input
capacitance cancellation.)

Still talking a about coax capacitance? Right

Your author says his 0.3pF input cap and FET buffer form a 1:17 divider,
implying T1's effective input capacitance is about 5pF. You should be
able to improve that by a factor of five without breaking a sweat, by a
factor of ten with a little more care.

Now is that from the 20meg moving to the T1 source, or some more from
Q1 or both?

Note I added the missing 0.3pf cap to the schematic.

Can I tell this is working if my 1X gain increases?
The 17 to 1 divider of the input cap and the gate capacitance and the 17
times gain of the amplifier equals 1X.

Say I get 80% T1 gate cancellation (by moving the 20Meg), now we have
effectively 1pf.
1pf/0.3pf = 3.33 and the amp gain 17 / 3.33 = 5.1
So I would think my total circuit gain would increase to 5.1.
Or do I not get it?
Mikek


+12V +12V
-+- -+-
I added 0.3pf cap | |
| | [22k] R4
| \| |
| Q1 |---+----------.
\|/ .<| | |
| | [47k] R5 |
(shield) | T1 |--' | |
------\|/ BF256C | === |
-------||-+----->|--+----------------|---//
------ | | Vdd |
| [10M] R1 | -+- |
| | | | |
| [10M] R2 | |/ Q2 |
| | .-----+---| |
| | | | |>. C1 |
| '---' R3[470] | 100n |
| | +---+--||--'
| === |R6 |
| [1K] '--||--.
| | 100n |
| === C2 |
'---------------------------------+
|
[22k] R7
|
===

Is that gain in a following amp? The amp shown here is a follower with
no gain.

--

Rick C

 

[rickman]

On 3/20/2017 6:21 PM, amdx wrote:

On 3/20/2017 3:34 PM, rickman wrote:
On 3/20/2017 2:16 PM, amdx wrote:
On 3/20/2017 11:29 AM, dagmargoodboat@yahoo.com wrote:

If you will look at my picture,
http://s395.photobucket.com/user/Qmavam/media/inside.jpg.html?o=163
you will notice I put the 470 ohm (turquoise resistor) on the other side
of the shield, (I don't know why).
What affect would that have?

On Monday, March 20, 2017 at 9:36:51 AM UTC-4, amdx wrote:
If you want to get fancier
and even lower input capacitance we can bootstrap the drain, too. A
bootstrapped shield for your pass-through (where you bring the input
through your metal box) would help, too.

OK, I'd like to get fancy, but I don't understand "A bootstrapped
shield" for my pass through.
I would like to understand physically what I need to do.

I have seen this done for electrometers where the concern is leakage
current. There they call it a "guard" ring. As James says, it will
also reduce input capacitance.

I don't understand how you can bootstrap the drain though. Since it is
connected to the positive rail, I'm not even sure what that means.


Here's another picture showing the input, there is 5/8" hole in the case
and I glued polystyrene sheet over it with the input wire coming out the
center.
http://i395.photobucket.com/albums/pp37/Qmavam/Input.jpg
Ah, here's a picture of a previous input cap, I don't use anymore, but
it shows the input better.
http://i395.photobucket.com/albums/pp37/Qmavam/1cmx1cmspaced5mm.jpg

This latter image doesn't look like what is used in this image.

http://s395.photobucket.com/user/Qmavam/media/inside.jpg.html

Was this just a temporary cap in place until you got the detail work
done?


Yes, that was a first iteration, nothing wrong with it, but it wasn't
as stable (two wires with a weights on the end) as my tiny piece of
double sided pcb.

Oh, so the free hanging copper is the old cap and the thing I can't see
is the PCB cap which you like better?

--

Rick C

 

[amdx]

On 3/20/2017 5:27 PM, rickman wrote:

On 3/20/2017 6:21 PM, amdx wrote:
On 3/20/2017 3:34 PM, rickman wrote:
On 3/20/2017 2:16 PM, amdx wrote:
On 3/20/2017 11:29 AM, dagmargoodboat@yahoo.com wrote:

If you will look at my picture,
http://s395.photobucket.com/user/Qmavam/media/inside.jpg.html?o=163
you will notice I put the 470 ohm (turquoise resistor) on the other
side
of the shield, (I don't know why).
What affect would that have?

On Monday, March 20, 2017 at 9:36:51 AM UTC-4, amdx wrote:
If you want to get fancier
and even lower input capacitance we can bootstrap the drain, too. A
bootstrapped shield for your pass-through (where you bring the input
through your metal box) would help, too.

OK, I'd like to get fancy, but I don't understand "A bootstrapped
shield" for my pass through.
I would like to understand physically what I need to do.

I have seen this done for electrometers where the concern is leakage
current. There they call it a "guard" ring. As James says, it will
also reduce input capacitance.

I don't understand how you can bootstrap the drain though. Since it is
connected to the positive rail, I'm not even sure what that means.


Here's another picture showing the input, there is 5/8" hole in the
case
and I glued polystyrene sheet over it with the input wire coming out
the
center.
http://i395.photobucket.com/albums/pp37/Qmavam/Input.jpg
Ah, here's a picture of a previous input cap, I don't use anymore, but
it shows the input better.
http://i395.photobucket.com/albums/pp37/Qmavam/1cmx1cmspaced5mm.jpg

This latter image doesn't look like what is used in this image.

http://s395.photobucket.com/user/Qmavam/media/inside.jpg.html

Was this just a temporary cap in place until you got the detail work
done?


Yes, that was a first iteration, nothing wrong with it, but it wasn't
as stable (two wires with a weights on the end) as my tiny piece of
double sided pcb.

Oh, so the free hanging copper is the old cap and the thing I can't see
is the PCB cap which you like better?

When you say can't see, do you mean it small and your looking side on
or do you mean you didn't see a link?
> http://s395.photobucket.com/user/Qmavam/media/inside.jpg.html?o=163

btw the 0.3pf cap is a approximately 1/8" disc of Teflon pcb 0.32"
thick. PCB material is not critical. Easy enough to set size, check the
gain of your amp without the input cap, then reduce the size of your
input cap until gain equals 1.
Mikek

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[amdx]

On 3/20/2017 5:25 PM, rickman wrote:

On 3/20/2017 6:15 PM, amdx wrote:
On 3/20/2017 2:31 PM, dagmargoodboat@yahoo.com wrote:

The idea is to shield your signal with coax, then to drive the coax's
shield to reduce the effect of the coax's capacitance.

In this case it was because I thought you were using a high-capacitance
(for the situation) signal feed-through, but it looks like you've
already done a very nice job providing low capacitance.

Here's another picture showing the input, there is 5/8" hole in the
case
and I glued polystyrene sheet over it with the input wire coming out
the
center.
http://i395.photobucket.com/albums/pp37/Qmavam/Input.jpg
Ah, here's a picture of a previous input cap, I don't use anymore, but
it shows the input better.
http://i395.photobucket.com/albums/pp37/Qmavam/1cmx1cmspaced5mm.jpg

The idea of bootstrapping is to provide a unity-gain buffer, then make
all the circuit nodes swing with the input voltage, so that the input
signal doesn't have to charge any of the nodes' capacitances.

This illustrates the ideas--

+12V +12V
-+- -+-
| |
| [22k] R4
\| |
Q1 |---+----------.
.<| | |
| [47k] R5 |
(shield) T1 |--' | |
------ BF256C | === |
----------+----->|--+----------------|---//
---+-- | | Vdd |
| [10M] R1 | -+- |
| | | | |
| [10M] R2 | |/ Q2 |
| | .-----+---| |
| | | | |>. C1 |
| '---' R3[470] | 100n |
| | +---+--||--'
| === |R6 |
| [1K] '--||--.
| | 100n |
| === C2 |
'---------------------------------+
|
[22k] R7
|
===

Q1 forces the drain to move up and down *with* the input signal,
cancelling Cgd. T1's source already follows the input signal,
reducing the effective Cgs.

I've shown Q2 driving a shield. It's optional--you likely don't need
that.

Ok, so if I was using short coax to connect to my LC, Q2 would drive
the shield to null it's capacitance.

I now use two 6" wires to clip to the LC. the two wire run about 2"
apart. I have wondered how much capacitance the leads add.
For a permanent test fixture with a tuning cap and a signal strength
meter, ready to plunk any coil into for testing this would be great use
of a fixed coax input.


If our buffer (Q2) and T1 together manage a gain of 0.8, we'll cancel
roughly 80% of the input capacitance. (A more complicated buffer
getting closer to unity gain would provide even better input
capacitance cancellation.)

Still talking a about coax capacitance? Right

Your author says his 0.3pF input cap and FET buffer form a 1:17 divider,
implying T1's effective input capacitance is about 5pF. You should be
able to improve that by a factor of five without breaking a sweat, by a
factor of ten with a little more care.

Now is that from the 20meg moving to the T1 source, or some more from
Q1 or both?

Note I added the missing 0.3pf cap to the schematic.

Can I tell this is working if my 1X gain increases?
The 17 to 1 divider of the input cap and the gate capacitance and the 17
times gain of the amplifier equals 1X.

Say I get 80% T1 gate cancellation (by moving the 20Meg), now we have
effectively 1pf.
1pf/0.3pf = 3.33 and the amp gain 17 / 3.33 = 5.1
So I would think my total circuit gain would increase to 5.1.
Or do I not get it?
Mikek


+12V +12V
-+- -+-
I added 0.3pf cap | |
| | [22k] R4
| \| |
| Q1 |---+----------.
\|/ .<| | |
| | [47k] R5 |
(shield) | T1 |--' | |
------\|/ BF256C | === |
-------||-+----->|--+----------------|---//
------ | | Vdd |
| [10M] R1 | -+- |
| | | | |
| [10M] R2 | |/ Q2 |
| | .-----+---| |
| | | | |>. C1 |
| '---' R3[470] | 100n |
| | +---+--||--'
| === |R6 |
| [1K] '--||--.
| | 100n |
| === C2 |
'---------------------------------+
|
[22k] R7
|
===

Is that gain in a following amp? The amp shown here is a follower with
no gain.

Yes, this is just the input, look back at Kleijers site, you will see
this without bootstraping and the rest of the amp.

http://www.crystal-radio.eu/fetamp/enfetamp.htm

Mikek

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[dcaster@krl.org]

On Monday, March 20, 2017 at 9:12:40 PM UTC-4, amdx wrote:

So glad to hear from you Jim!
Good luck on your recovery!

Mikek

Good to hear from you. I hope things go better now.

Dan

 

[billbowden]

"rickman" <gnuarm@gmail.com> wrote in message
newsan4s4$99i$1@dont-email.me...

On 3/19/2017 7:31 PM, billbowden wrote:
"amdx" <nojunk@knology.net> wrote in message
newsam0ee$ch5$1@dont-email.me...
On 3/14/2017 11:18 PM, billbowden wrote:
Which is a better design. Suppose you have a 6 inch length of PVC pipe
with
numerous turns of wire that has an inductance of say 200uH. Now suppose
you
use the same (6 inch) piece of PVC with a ferrite rod in the core with
considerably fewer turns of wire. Which one would capture the most
signal
at the AM Broadcast frequencies (500K to 2 Megs) and produce the
greatest
signal output? Would it be more ferrite, or more wire?


I'll run the experiment.

Do you want it tuned?

If not, I have no way to measure the signals of my local stations.
I need the resonance peaking to see the signal.

What diameter PVC?

I have 1/2" OD polystyrene that will allow a little closer coupling
between the ferrite and the wire. 400 turns #28 = 203uh air core.

I have 1/2" CPVC. actual OD. 0.615"
290 turns #28 = 200uh air core


I have 1/2 PVC, actual OD. 0.832. 175 turns #28 = 205uh air core.

Pick one.

I'll also wind one with less turns and use my best Q rod that is 8" long
x
0.375" diameter.

I will check three frequencies, 590Khz, 1290kHz and 1430Khz.

I made a post last night of the wrong experiment (6"dia not 6" long)
It has not shown up this morning, so I'll repeat my measurement method.

To measure the signal I have a very high input impedance amp with a
gain
of 1.
I use the amp to drive a scope (ch 2) set at 50mV/div. I took the
channel
2 output from the back of the scope to drive a Boonton 92BD RF millivolt
meter. I use the scope to compare the visual to audio from a portable
radio to know where I am tuned.
Modulation causes a bit of amplitude bounce, but I do a visual average.

Let me know what you want.
Mikek


Actually, I'm just interested in comparing the response of two identical
loopsticks, one using an air core and the other using a ferrite core. I
could do the experiment since there is a 50KW station about 7 miles away
and
I can see the signal from the antenna loop directly on a scope. I can get
about 1 volt peak using a loop antenna of about 15 inches square. I just
thought someone would know the answer without a lot of experimenting. I
have
a portable car radio with a air core loop antenna mounted on the chassis
that measures 6.5 inch by 3/4 diameter and about 300 turns of small wire.
Works fine and gets stations 130 miles away. But it's a power hog and
draws
100mA from a 12 volt battery. I suppose a good test would be to use a
shorter ferrite rod and fewer turns to compare the results. But I'm lazy
and
just want to know which idea is better.

Connecting a scope directly to a loop antenna may cause a loss of Q. I'm
hoping not, as I am building a very high Q antenna that will depend on a
high impedance not sapping it, but it depends on the antenna. The point
is if your measurement saps the Q, then any impact on the Q by the ferrite
will not be noticed.

I just looked at my 15 inch square (air core) loop antenna on a scope. The
amplitude was about 1 volt P-P. I connected a 150K resistor across the loop
and the amplitude dropped to about half that. So, the impedance looks to be
about 150K. The scope input is 1 Meg and 30pF and I used a 10X probe. The Q
of the antenna was measured at 300 at the low end of the band (600Khz) and
200 at the high end. That was using a Boonton Q meter. So, it doesn't look
like connecting a scope has much effect on Q in this case. But possibly
doing the same test on a short ferrite loop would give different results.
Actually, the Q of the loop should be about 100 or less if you want a 10Khz
bandwidth.

 

[amdx]

On 3/20/2017 6:41 PM, billbowden wrote:

"rickman" <gnuarm@gmail.com> wrote in message
newsan4s4$99i$1@dont-email.me...
On 3/19/2017 7:31 PM, billbowden wrote:
"amdx" <nojunk@knology.net> wrote in message
newsam0ee$ch5$1@dont-email.me...
On 3/14/2017 11:18 PM, billbowden wrote:
Which is a better design. Suppose you have a 6 inch length of PVC pipe
with
numerous turns of wire that has an inductance of say 200uH. Now suppose
you
use the same (6 inch) piece of PVC with a ferrite rod in the core with
considerably fewer turns of wire. Which one would capture the most
signal
at the AM Broadcast frequencies (500K to 2 Megs) and produce the
greatest
signal output? Would it be more ferrite, or more wire?


I'll run the experiment.

Do you want it tuned?

If not, I have no way to measure the signals of my local stations.
I need the resonance peaking to see the signal.

What diameter PVC?

I have 1/2" OD polystyrene that will allow a little closer coupling
between the ferrite and the wire. 400 turns #28 = 203uh air core.

I have 1/2" CPVC. actual OD. 0.615"
290 turns #28 = 200uh air core


I have 1/2 PVC, actual OD. 0.832. 175 turns #28 = 205uh air core.

Pick one.

I'll also wind one with less turns and use my best Q rod that is 8" long
x
0.375" diameter.

I will check three frequencies, 590Khz, 1290kHz and 1430Khz.

I made a post last night of the wrong experiment (6"dia not 6" long)
It has not shown up this morning, so I'll repeat my measurement method.

To measure the signal I have a very high input impedance amp with a
gain
of 1.
I use the amp to drive a scope (ch 2) set at 50mV/div. I took the
channel
2 output from the back of the scope to drive a Boonton 92BD RF millivolt
meter. I use the scope to compare the visual to audio from a portable
radio to know where I am tuned.
Modulation causes a bit of amplitude bounce, but I do a visual average.

Let me know what you want.
Mikek


Actually, I'm just interested in comparing the response of two identical
loopsticks, one using an air core and the other using a ferrite core. I
could do the experiment since there is a 50KW station about 7 miles away
and
I can see the signal from the antenna loop directly on a scope. I can get
about 1 volt peak using a loop antenna of about 15 inches square. I just
thought someone would know the answer without a lot of experimenting. I
have
a portable car radio with a air core loop antenna mounted on the chassis
that measures 6.5 inch by 3/4 diameter and about 300 turns of small wire.
Works fine and gets stations 130 miles away. But it's a power hog and
draws
100mA from a 12 volt battery. I suppose a good test would be to use a
shorter ferrite rod and fewer turns to compare the results. But I'm lazy
and
just want to know which idea is better.

Connecting a scope directly to a loop antenna may cause a loss of Q. I'm
hoping not, as I am building a very high Q antenna that will depend on a
high impedance not sapping it, but it depends on the antenna. The point
is if your measurement saps the Q, then any impact on the Q by the ferrite
will not be noticed.


I just looked at my 15 inch square (air core) loop antenna on a scope. The
amplitude was about 1 volt P-P. I connected a 150K resistor across the loop
and the amplitude dropped to about half that. So, the impedance looks to be
about 150K. The scope input is 1 Meg and 30pF and I used a 10X probe. The Q
of the antenna was measured at 300 at the low end of the band (600Khz) and
200 at the high end. That was using a Boonton Q meter. So, it doesn't look
like connecting a scope has much effect on Q in this case. But possibly
doing the same test on a short ferrite loop would give different results.
Actually, the Q of the loop should be about 100 or less if you want a 10Khz
bandwidth.

Sounds about right, the coil I measured has a Q of 1000 to 1400 at
800kHz. If we say it is Q = 1200 and the Reactance at 800kHz is 1,166
ohms, the resonant peak will be 1.33Megohms.
btw, I also measured my Qs with a Boonton 260. I had to reduce the
injection voltage (Multiplier) way down in order to make that high Q
measurement,
Mikek


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On Mon, 20 Mar 2017 10:48:00 -0700 (PDT), tabbypurr@gmail.com wrote:

On Monday, 20 March 2017 17:06:41 UTC, k...@notreal.com wrote:
On Sun, 19 Mar 2017 19:22:33 -0700 (PDT), tabbypurr wrote:
On Sunday, 19 March 2017 23:54:09 UTC, k...@notreal.com wrote:
On Sun, 19 Mar 2017 09:16:29 -0000, "Kevin Aylward"
kevinRemovAT@kevinaylward.co.uk> wrote:
"Kevin Aylward" wrote in message
news:kfudnRgqWLyQIlDFnZ2dnUU7-XvNnZ2d@giganews.com...

"bitrex" wrote in message news:9DdzA.62942$mb5.42260@fx19.iad...


I'm a liberal and yet, in some circumstances I do support the death
penalty.

I don't see that there can be much more of a cold-bloodied, calculated
murder, than having 12 people calmly sit on seats debating the merits of
killing someone over several days, with a state sponsored judge exposing
all sorts of "rational" arguments as to how it is ethically justifiable to
execute said person being debated. Said person is then dragged to a room
with gawking onlookers watching the deliberate injection of chemicals to
terminate said life. This is no less barbaric than at a Roman gladiator ring
where the emperor points his thump up or down.

What is even more grotesque, is that large numbers of those barbarians
supporting state sponsored murder are alleged Christians, despite their role
model, Jesus, emphatically instructing them that "thou shall not kill".
More, stunningly the xtians claim that it is they that there the morally
righteous ones.

The perp gave up his right to life by taking that of another. End of
story.

Now there's simplistic.

Yes, it really is so simple that even you should be able to
understand.

I understand it ok. You're seriously naive if you think it's that simple. Let's just agree to disagree.

Evidently not.