Driver to drive?

[Tauno Voipio]

On 19.3.17 04:15, Clifford Heath wrote:

good 40 dB lower than a strong mixer.

Thank you. I didn't realize they used series Schottky strings.

Could the need be somewhat averted with back bias instead?

The diode ring works only because there is a forward
voltage drop in the diodes. The forward drop clips the
injection voltage to square wave and it limits the
signal level to well below the clipping level.

The series diode rings were used already in the SSB
channeled telephone circuits in the 1930's to get
higher levels on the modulators.

--

-TV

 

[Tauno Voipio]

On 20.3.17 13:26, pcdhobbs@gmail.com wrote:

The Tayloe approach uses a mux, but is the same basic idea, and aiui it came along much later. So I think it should be called the Oxner mixer.

Cheers

Phil Hobbs

In the same sense, we can say that the Oxner FET switch
ring uses the reversing switch principle of the selenium
rectifier rings of telephony SSB channels years before
any FETs.

--

-TV

 

On Tuesday, March 21, 2017 at 8:54:35 AM UTC-4, amdx wrote:

On 3/20/2017 10:25 PM, rickman wrote:
On 3/20/2017 10:23 PM, amdx wrote:
On 3/20/2017 8:28 PM, rickman wrote:
On 3/20/2017 9:09 PM, amdx wrote:

I'm sure it could be built with a couple of opamps. It is a 50 ohm
output. Could probably do better, this starts to distort at I think
8 Vpp. But I don't have any antenna that need much that headroom.

That's 8Vpp open circuit, 4Vpp loaded.

Well then, eazy peazy. I used a circuit that used positive feedback to
make the output impedance look higher than the resistor in the circuit.
I think I used 12.5 or maybe it was just 12 and got multiplied by 4.
This makes the calculation of the gain a little more complex so you
would not be able to adjust the gain with a pot or anything... unless it
was on an earlier stage.

The middle stage with the single transistor, anything special about
that? It has a connection with caps I'm not familiar with from the
emitter to the input. That would be a low level of positive feedback I
believe. Any idea why?

He's bootstrapping the input impedance to avoid loading the FET stage.
Kleijer's crafty.

Hey I'm a semi-retired shrimp seller with a little bit of technical
skill. I did a good job of replicating the circuit, I didn't design it.
I can only explain operation on a simple level. If I had more knowledge
I would have corrected the distortion at increased input levels.
I suspect a good analog engineer would have done a lot of things
different to reach the goal of high input impedance, 50 ohm output. On
the other hand Kleijer built a working circuit and later went back and
built an improved second version. I follow the crystal radio community
and have not heard of anyone else that built the circuit, it's a shame
because it is a very useful piece of equipment for experimenting with
high Q LC circuits.

ISTM Kleijer did a very decent job, and got something more than good
enough for his task. And was nice enough to share it with everyone.
+1 for Kleijer.

> I hope to take dagmar's design and improve it further.

We could do that, but it would add complexity without much benefit to
your application. Using an op-amp buffer instead of a BJT follower is
one possibility...

I designed an opamp circuit to output an 8 volt signal with a 12 volt
supply into 50 ohm cable. I didn't quite get 8 volts before it starts
to distort, but it was close. I believe the gain-bandwidth product of
the amp was over 30 MHz, so it should do ok at 10 MHz and no gain. But
then you need a little gain I guess. Opps, no, the GB was 15 MHz.

Wait a minute!!! That bootstrap of the input resistors won't work. The
470 ohm source resistor is there to set a bias point with the source
higher than the gate. The resistors are there to set the DC voltage of
the gate to ground. Perhaps a cap could be used to feed the point
between the two resistors?

There's nothing stopping us from running the JFET at Vgs=0. That just
runs it richer.

I just realized that is the purpose of the two caps on T2 emitter to the
47 ohm resistor. It allows the resistors to set the DC operating point
but bootstraps their capacitance. No?

??
I have looked for a data sheet on the BF256C, all I can find is very
limited info, Anyone find a data sheet with the device capacitances?
Mikek

In the old days, all the various JFETs were selections taken from one
of several different processes. Fairchild's BF256B datasheet says it's
made on Process 50, so it should have pretty much the same capacitances
as any other JFET from the same process, e.g.,
https://www.fairchildsemi.com/datasheets/MM/MMBF5484.pdf

Cheers,
James Arthur

 

On Tuesday, 21 March 2017 01:08:46 UTC, Jim Thompson wrote:

On Tue, 14 Mar 2017 18:58:32 -0700, Jim Thompson
To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> 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

Well the docs tried to kill me, but I survived a very unpleasant trip.

They put a stent in my bile duct, but in recovery they discovered my
kidneys couldn't cope, and went into failure

So a one-day outpatient "procedure" ended up being a nasty 6-day
battle with helping the kidneys to recover.

Thanks to all for your good wishes!

...Jim Thompson

Welcome back. That sounds fairly grim.


NT

 

[amdx]

On 3/21/2017 2:19 AM, dagmargoodboat@yahoo.com wrote:

On Monday, March 20, 2017 at 9:49:55 PM UTC-4, dagmarg...@yahoo.com wrote:
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.

I thought about this a bit and came up with an improved follower.

The main limitation of the previous circuit was the FET's poor performance
as a voltage-follower. Unaided, the T1 has a gain of about 0.6. That hits
our bootstrapping from all sides. First, c(gs) (the largest capacitance)
is only bootstrapped by 60%, leaving 40% of the BC547C's ~5pF c(gs). Next,
we use that voltage to drive our less-than-unity Q2, which drives less-than-
unity Q1. This all adds up.

Changing T1's load to a current sink makes T1 into a much better follower,
increasing voltage gain from 0.6 to about 0.95. The better 'follower'
action now bootstraps away nearly all of c(gs) (T1's largest capacitance),
and gives us a better signal to drive the drain bootstrap as well. Good,
good, and good. And not terribly much trouble to do, either.

Vdd Vdd
-+- -+-
| |
| [22k] R5
Q1 \| |
BC547B |---+-------.
.<| | |
| [47k] R6 |
(shield) T1 |--' | |
------ BF256C | === |
----------+----->|--. |
---+-- | | Vdd --- C2
| | | -+- ---100n
| | | | |
| R1 [10M] | |/ Q2 |
| | +---| BC547B |
| | | |>. |
| | R3 [470] | |
| | | | | C3
| | | | | 100n
| +----||---+-----+-------+-----||---> to ampl.
| | C1 | |
| R2 [10M] 100pF R4 [470] --- C4
| | | --- 100n
| === === |
| |
'------------------------------+
|
Cin ~200fF [2.2k] R7
|
===

Cheers,
James Arthur

Thanks for the time.
As it is now constructed the enclosure is the shield.
Is that good or bad? ie. Should the enclosure be isolated from the shield?

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On Sat, 18 Mar 2017 19:11:21 -0700 (PDT), pcdhobbs@gmail.com wrote:

I've used them in instruments but never in receivers. Gilbert cells are _not_ strong mixers
--they have many fine qualities, but good IMD performance is not one of
them.

Interesting. Please educate me - when you say "strong" do you mean
"involving sharp switching"? Is is Miller effect and LO feedthrough
that limits the "strength"? Does HFA3101 not qualify as "strong"?

A strong mixer is one with really good IMD performance. Antennas pick up everything at some level, so the amount of stuff that your poor little RX front end has to cope with is pretty appalling.

A diode bridge with 2 or 3 series-connected Schottky diodes in each arm and a +17 dBm LO is one decent approach, and you can get one from Mini Circuits in one day if you like.

A bridge made from a fast CMOS mux is another good approach, though it takes more manual work.

These techniques use square wave switching (or nearly), which greatly reduces the proportion of the time when the switching devices are in their 'linear' range.

In order to make an order-1 change in the behaviour of a Level 17 mixer or a FET MUX, an interfering signal has to be pretty big, i.e. a volt or two.

To do the same to a Gilbert cell requires about e/kT, i.e. ~26 mV. So on a simplistic analysis, a Gilbert cell becomes nonlinear at levels a good 40 dB lower than a strong mixer.

Cheers

Phil Hobbs

The question about the pros and cons of different mixers might soon be
in the past, since direct sampling ADCs perform surprisingly well.

One WebSDR receiver (http://websdr.ewi.utwente.nl:8901/) samples the
0-30 MHz band and then digitally decimates the requested sub-band for
individual listeners across the Internet. Unfortunately, the antenna
is in the middle of a noisy campus area, thus it is hard to say
something about the actual weak signal performance. However, I didn't
detect any obvious spurious responses as with some ordinal receivers.

For single frequency reception at one time, much slower sampling rates
(fs) and hence cheaper or more accurate ADCs can be used by limiting
the analog front end bandwidth well below fs/s then undersampling,
thus no need for a mixer in front of the ADC.

 

[amdx]

On 3/20/2017 10:25 PM, rickman wrote:

On 3/20/2017 10:23 PM, amdx wrote:
On 3/20/2017 8:28 PM, rickman wrote:
On 3/20/2017 9:09 PM, amdx wrote:
On 3/20/2017 7:55 PM, rickman wrote:
On 3/20/2017 6:54 PM, amdx wrote:
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.

I just meant it is small and I couldn't see what it was. Initially I
thought it might be a small value ceramic cap you put in place to
check
out the amp before you optimized the cap. Now I realize it is a very
small piece of PCB and *is* the optimized cap. I also didn't know
which
image was earlier and which was later.

Why would you adjust the overall circuit gain by trimming the cap?
The
amp gain can be trimmed, no?

I'm sure the amp can be changed, but the end game was to make the
input
cap small, I couldn't go much smaller.

What frequency range is this amp intended to be used for? Nearly all
the stuff I've seen where Q matters is LF or MF.

Kleijer says it's flat from 10kHz to 10 MHz.

They use loop antennas
for higher frequencies, but with too high Q the bandwidth gets so
narrow
even voice won't get through, just CW.

Most of the stuff I'm looking at is crystal radio, by the time you
start driving a headphone your Q gets lowered a lot. I never hear the
crystal radio guys complain about lack of bandwidth.

Some of the antennas Kleijer uses I would think would limit the
bandwidth of his circuits with Q of over 1000.

Again not a common problem, but easy to fix with a load resistor.

If the headphones or load resistor limit the Q, what is the bleeping
point of all that Litz wire and custom tuning capacitor stuff? I
thought the whole point was to get the Q as high as possible.

Yes, it is. But you still need to get the maximum power out to drive
your headphones.
In a perfect system, you would drop your Q by half to get maximum
audio. But the diode gets involved and that I can't decipher.


If you start with a Q over 1000 and end up with a few hundred, I
wouldn't
expect that to be distinguishable from a coil with a Q of some hundreds
which is where Kleijer started in his coil investigations.

This is radio dxing, grab every db of signal!


If the frequencies are not so high, why not use an opamp for the final
stage rather than the much more complex push-pull stage? I assume
that
is intended to be in essence a "power" output stage and does not
otherwise contribute significantly to the characteristics of the
rest of
the circuit.

I'm sure it could be built with a couple of opamps. It is a 50 ohm
output. Could probably do better, this starts to distort at I think
8 Vpp. But I don't have any antenna that need much that headroom.

That's 8Vpp open circuit, 4Vpp loaded.

Well then, eazy peazy. I used a circuit that used positive feedback to
make the output impedance look higher than the resistor in the circuit.
I think I used 12.5 or maybe it was just 12 and got multiplied by 4.
This makes the calculation of the gain a little more complex so you
would not be able to adjust the gain with a pot or anything... unless it
was on an earlier stage.

The middle stage with the single transistor, anything special about
that? It has a connection with caps I'm not familiar with from the
emitter to the input. That would be a low level of positive feedback I
believe. Any idea why?

Hey I'm a semi-retired shrimp seller with a little bit of technical
skill. I did a good job of replicating the circuit, I didn't design it.
I can only explain operation on a simple level. If I had more knowledge
I would have corrected the distortion at increased input levels.
I suspect a good analog engineer would have done a lot of things
different to reach the goal of high input impedance, 50 ohm output. On
the other hand Kleijer built a working circuit and later went back and
built an improved second version. I follow the crystal radio community
and have not heard of anyone else that built the circuit, it's a shame
because it is a very useful piece of equipment for experimenting with
high Q LC circuits.
I hope to take dagmar's design and improve it further.

I designed an opamp circuit to output an 8 volt signal with a 12 volt
supply into 50 ohm cable. I didn't quite get 8 volts before it starts
to distort, but it was close. I believe the gain-bandwidth product of
the amp was over 30 MHz, so it should do ok at 10 MHz and no gain. But
then you need a little gain I guess. Opps, no, the GB was 15 MHz.

Wait a minute!!! That bootstrap of the input resistors won't work. The
470 ohm source resistor is there to set a bias point with the source
higher than the gate. The resistors are there to set the DC voltage of
the gate to ground. Perhaps a cap could be used to feed the point
between the two resistors?

I just realized that is the purpose of the two caps on T2 emitter to the
47 ohm resistor. It allows the resistors to set the DC operating point
but bootstraps their capacitance. No?

??
I have looked for a data sheet on the BF256C, all I can find is very
limited info, Anyone find a data sheet with the device capacitances?
Mikek



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[Phil Hobbs]

On 03/21/2017 06:33 AM, Tauno Voipio wrote:

On 20.3.17 13:26, pcdhobbs@gmail.com wrote:

The Tayloe approach uses a mux, but is the same basic idea, and aiui
it came along much later. So I think it should be called the Oxner mixer.

Cheers

Phil Hobbs


In the same sense, we can say that the Oxner FET switch
ring uses the reversing switch principle of the selenium
rectifier rings of telephony SSB channels years before
any FETs.

I don't agree. Diodes and transistors work differently in mixers (as
elsewhere) because their control and signal paths are separate.

The two-transformer ring DBM is also a thing of beauty, but I don't know
who invented it. I think that it's a pity that in electronics we
usually don't attach people's names to stuff the way it's done in
science. Gilbert cells, Oxner mixers, Brokaw bandgaps, Widlar
practically everythings, Eccles-Jordan flipflops, Johnson noise, Nyquist
frequency....bring 'em on.

It helps maintain the ethos of the field, I think, and encourages people
that you don't have to walk on water or be 200 years old to have a
circuit named after you.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[Phil Hobbs]

On 03/21/2017 08:39 AM, upsidedown@downunder.com wrote:

On Sat, 18 Mar 2017 19:11:21 -0700 (PDT), pcdhobbs@gmail.com wrote:

I've used them in instruments but never in receivers. Gilbert
cells are _not_ strong mixers --they have many fine qualities,
but good IMD performance is not one of
them.

Interesting. Please educate me - when you say "strong" do you
mean "involving sharp switching"? Is is Miller effect and LO
feedthrough that limits the "strength"? Does HFA3101 not qualify
as "strong"?

A strong mixer is one with really good IMD performance. Antennas
pick up everything at some level, so the amount of stuff that your
poor little RX front end has to cope with is pretty appalling.

A diode bridge with 2 or 3 series-connected Schottky diodes in each
arm and a +17 dBm LO is one decent approach, and you can get one
from Mini Circuits in one day if you like.

A bridge made from a fast CMOS mux is another good approach, though
it takes more manual work.

These techniques use square wave switching (or nearly), which
greatly reduces the proportion of the time when the switching
devices are in their 'linear' range.

In order to make an order-1 change in the behaviour of a Level 17
mixer or a FET MUX, an interfering signal has to be pretty big,
i.e. a volt or two.

To do the same to a Gilbert cell requires about e/kT, i.e. ~26 mV.
So on a simplistic analysis, a Gilbert cell becomes nonlinear at
levels a good 40 dB lower than a strong mixer.

Cheers

Phil Hobbs

The question about the pros and cons of different mixers might soon
be in the past, since direct sampling ADCs perform surprisingly
well.

One WebSDR receiver (http://websdr.ewi.utwente.nl:8901/) samples the
0-30 MHz band and then digitally decimates the requested sub-band
for individual listeners across the Internet. Unfortunately, the
antenna is in the middle of a noisy campus area, thus it is hard to
say something about the actual weak signal performance. However, I
didn't detect any obvious spurious responses as with some ordinal
receivers.

For single frequency reception at one time, much slower sampling
rates (fs) and hence cheaper or more accurate ADCs can be used by
limiting the analog front end bandwidth well below fs/s then
undersampling, thus no need for a mixer in front of the ADC.

Maybe. Seems like a lot of foofaraw just for a sportscast.

SDR-style spectrum analyzers are pretty much entry-level junk compared
with the traditional approach. Lots of bells and whistles, lots faster
measurements, but in my world if you can't measure something,
not-measuring it fast is no better than not-measuring it slowly.

Cheers

Phil "Big boat anchor fan" Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[Phil Hobbs]

On 03/17/2017 08:31 PM, George Herold wrote:

On Friday, March 17, 2017 at 11:38:44 AM UTC-4, Phil Hobbs wrote:
On 03/17/2017 11:28 AM, George Herold wrote:
On Friday, March 17, 2017 at 10:30:32 AM UTC-4, John Larkin wrote:
On Thu, 16 Mar 2017 18:46:06 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

On Thursday, March 16, 2017 at 8:36:16 PM UTC-4, Phil Allison wrote:
George Herold wrote:



I've got an AM radio that came with an air core antenna.
(1990's vintage)
~4" (10 cm) squarish loop. Not sure how many turns.
Works fine.


** So it's an external loop for a main powered receiver ?

Right, It's a JVC "ultra compact component system"
FS-1000


** So why didn't you post that info before?

'cos I'm now at home and not at work.
It's a fucking frame antenna, already discussed here in this thread and been around since the dawn of radio.



Knowing almost nothing about AM, (and assuming I don't care about price.)
I figure I want the highest Q possible on the front end..


** Nope.

You need at least 10kHz of bandwidth at the antenna so the Q must not exceed 50 to 100 across the AM band. You will find that antenna has a fairly low Q in practice.
OK I was thinking of best signal to noise, and figuring that ~1-2 kHz would
be enough.. Everyones "best/ optimal" is a bit different.

An AM antenna doesn't need to be tuned at all. An untuned coil will
snoop the ambient h-field.
I guess that's right. As long as most of the noise is "in the air" it doesn't
really matter where the band pass filter is. (Except for dynamic range issues.)

As you say, dynamic range. An untuned input needs a stronger mixer. A
Q of 10 or 20 would help a lot.

On the other hand, one could just use a Mini Circuits mixer with a +17
dBm LO, or a nice analogue mux with square wave drive. It takes a lot
to screw one of those up.
Hah, I made an AM radio just that way. Not with a loop, but just
a length of wire. (It's probably the worlds's worst AM radio.)

Probably a lot better than most, especially in the mixer department.
Cobbling together synthesizers and MCL parts with BNC cables is an
amazingly fast and effective way of measuring stuff, if you're any good
at it.

I learned RF in the palmy days of my youth, as I've discussed here
before--I got chucked right in the deep end, having to design high
performance frequency control modules for the world's first civilian DBS
system, starting from an astronomy degree and a hobby background. I'd
read about PLLs, but never seen one to know what it was, let alone
designed one.

Talk about dumb luck. I'd never have come up to speed that fast otherwise.

I had to add series L's (selected for range) to make it work.
Circuit from Terman's radio electronics book.

Well, even you probably didn't have a big enough back yard for a half
wave dipole at 540 kHz. So there's no shame in a loading coil for that.

So a loop (with parallel C) into a TIA? ... (I'd rather use an opamp.)
or will that wig out at the C side of the resonance?

For a high-Z antenna like that I'd probably use a bootstrapped JFET
follower front end, with appropriate protection diodes and probably a
couple of LND150s to limit the diode current. You really can get gains
of 0.9997 that way, with pretty decent bandwidth. There's not a lot of
room for distortion to hide in a circuit like that.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[Cursitor Doom]

On Mon, 20 Mar 2017 20:23:37 -0400, krw wrote:

It's obvious you're illiterate.

no point in reading further

I feel I should at this point apologise for the remarks made by my fellow
countryman, Kev. He and the poster "tabbypurr" are both singularly ill-
informed on this issue. Their ignorance is only matched by their
indefatigable ability to repeat the same dogma over and over and over
again. You will never win an argument against them; they simply won't
listen to reason. Do yourself a big favour and mark the thread "ignore"
in your newsreader. You'll save yourself from a huge amount of wasted
time.

 

[John Robertson]

On 2017/03/20 11:14 PM, dagmargoodboat@yahoo.com wrote:

On Monday, March 20, 2017 at 9:08:46 PM UTC-4, Jim Thompson wrote:
On Tue, 14 Mar 2017 18:58:32 -0700, Jim Thompson
To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> 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

Well the docs tried to kill me, but I survived a very unpleasant trip.

They put a stent in my bile duct, but in recovery they discovered my
kidneys couldn't cope, and went into failure

So a one-day outpatient "procedure" ended up being a nasty 6-day
battle with helping the kidneys to recover.

Thanks to all for your good wishes!

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| STV, Queen Creek, AZ 85142 Skype: skypeanalog | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

Thinking outside the box... producing elegant solutions.

Shucks Jim, welcome back!

Cheers,
James Arthur

Indeed, the signal to noise ratio was getting too large!

We missed you.

John

 

On Tuesday, March 21, 2017 at 12:54:05 PM UTC-4, amdx wrote:

On 3/21/2017 9:57 AM, dagmargoodboat@yahoo.com wrote:
On Tuesday, March 21, 2017 at 8:54:35 AM UTC-4, amdx wrote:
On 3/20/2017 10:25 PM, rickman wrote:
On 3/20/2017 10:23 PM, amdx wrote:
On 3/20/2017 8:28 PM, rickman wrote:
On 3/20/2017 9:09 PM, amdx wrote:

I'm sure it could be built with a couple of opamps. It is a 50 ohm
output. Could probably do better, this starts to distort at I think
8 Vpp. But I don't have any antenna that need much that headroom.

That's 8Vpp open circuit, 4Vpp loaded.

Well then, eazy peazy. I used a circuit that used positive feedback to
make the output impedance look higher than the resistor in the circuit.
I think I used 12.5 or maybe it was just 12 and got multiplied by 4.
This makes the calculation of the gain a little more complex so you
would not be able to adjust the gain with a pot or anything... unless it
was on an earlier stage.

The middle stage with the single transistor, anything special about
that? It has a connection with caps I'm not familiar with from the
emitter to the input. That would be a low level of positive feedback I
believe. Any idea why?

He's bootstrapping the input impedance to avoid loading the FET stage.
Kleijer's crafty.

Hey I'm a semi-retired shrimp seller with a little bit of technical
skill. I did a good job of replicating the circuit, I didn't design it.
I can only explain operation on a simple level. If I had more knowledge
I would have corrected the distortion at increased input levels.
I suspect a good analog engineer would have done a lot of things
different to reach the goal of high input impedance, 50 ohm output. On
the other hand Kleijer built a working circuit and later went back and
built an improved second version. I follow the crystal radio community
and have not heard of anyone else that built the circuit, it's a shame
because it is a very useful piece of equipment for experimenting with
high Q LC circuits.

ISTM Kleijer did a very decent job, and got something more than good
enough for his task. And was nice enough to share it with everyone.
+1 for Kleijer.

I hope to take dagmar's design and improve it further.

We could do that, but it would add complexity without much benefit to
your application. Using an op-amp buffer instead of a BJT follower is
one possibility...

I worded that poorly, I meant, take dagmar's design to further improve
Kleijers design.
I hack, I don't design.
Mikek

Oh I'm not offended, trust me. I was agreeing with you that my circuit's
performance could be improved on. I'm well aware, we just don't need it.
Give me one more transistor and it could be markedly better still, but
we don't need it. It's a waste to overcomplicate a thing.

I was also giving thumbs-up to Kleijer. A schematic is a window into the
designer's soul. Kleijer has soul.

Cheers,
James Arthur

 

[Cursitor Doom]

On Mon, 20 Mar 2017 18:08:35 -0700, Jim Thompson wrote:

Well the docs tried to kill me, but I survived a very unpleasant trip.

They put a stent in my bile duct, but in recovery they discovered my
kidneys couldn't cope, and went into failure

So a one-day outpatient "procedure" ended up being a nasty 6-day battle
with helping the kidneys to recover.

Thanks to all for your good wishes!

Welcome back, Jim! The Lefties were getting a bit of a free run in your
absence, spreading their old, discredited nonsense around. ;->

 

[George Herold]

On Tuesday, March 21, 2017 at 3:06:01 PM UTC-4, piglet wrote:

On 21/03/2017 13:42, Phil Hobbs wrote:

The two-transformer ring DBM is also a thing of beauty, but I don't know
who invented it. I think that it's a pity that in electronics we
usually don't attach people's names to stuff the way it's done in
science. Gilbert cells, Oxner mixers, Brokaw bandgaps, Widlar
practically everythings, Eccles-Jordan flipflops, Johnson noise, Nyquist
frequency....bring 'em on.

It helps maintain the ethos of the field, I think, and encourages people
that you don't have to walk on water or be 200 years old to have a
circuit named after you.

Cheers

Phil Hobbs


Hail the Hobbs Bootstrap!

There is the Graetz-Pollak diode bridge but that is what we know as the
full wave bridge rectifier.

The Ring modulator DBM is due to Cowan-Keith.

piglet

I first say the cap multiplier in Phil's book, for about 1 year I called it
a Hobbs Filter in my notebook. Short lived fame. :^)

George H.

 

[amdx]

On 3/21/2017 9:28 AM, dagmargoodboat@yahoo.com wrote:

On Tuesday, March 21, 2017 at 8:27:51 AM UTC-4, amdx wrote:
On 3/21/2017 2:19 AM, dagmargoodboat@yahoo.com wrote:
On Monday, March 20, 2017 at 9:49:55 PM UTC-4, dagmarg...@yahoo.com wrote:
On Monday, March 20, 2017 at 6:15:37 PM UTC-4, amdx wrote:

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.

I thought about this a bit and came up with an improved follower.

The main limitation of the previous circuit was the FET's poor performance
as a voltage-follower. Unaided, the T1 has a gain of about 0.6. That hits
our bootstrapping from all sides. First, c(gs) (the largest capacitance)
is only bootstrapped by 60%, leaving 40% of the BC547C's ~5pF c(gs). Next,
we use that voltage to drive our less-than-unity Q2, which drives less-than-
unity Q1. This all adds up.

Changing T1's load to a current sink makes T1 into a much better follower,
increasing voltage gain from 0.6 to about 0.95. The better 'follower'
action now bootstraps away nearly all of c(gs) (T1's largest capacitance),
and gives us a better signal to drive the drain bootstrap as well. Good,
good, and good. And not terribly much trouble to do, either.

Vdd Vdd
-+- -+-
| |
| [22k] R5
Q1 \| |
BC547B |---+-------.
.<| | |
| [47k] R6 |
(shield) T1 |--' | |
------ BF256C | === |
----------+----->|--. |
---+-- | | Vdd --- C2
| | | -+- ---100n
| | | | |
| R1 [10M] | |/ Q2 |
| | +---| BC547B |
| | | |>. |
| | R3 [470] | |
| | | | | C3
| | | | | 100n
| +----||---+-----+-------+-----||---> to ampl.
| | C1 | |
| R2 [10M] 100pF R4 [470] --- C4
| | | --- 100n
| === === |
| |
'------------------------------+
|
Cin ~200fF [2.2k] R7
|
===

Cheers,
James Arthur

Thanks for the time.
As it is now constructed the enclosure is the shield.
Is that good or bad? ie. Should the enclosure be isolated from the shield?

The enclosure should be grounded! Let's not confuse that with
bootstrapping the input coax's shield (which you'll only do _if_
you use coax).

So yes, the enclosure should be isolated from the driven shield that is
shown in the schematic.

OK, so I ground the enclosure to (battery) ground and use an isolated
input connector. I have some isolated BNC connectors that will work great.

(My shield-driver is pretty wimpy, only suitable for a very short, low-
capacitance run. Might need beefing up.)

My plan is to build this into a setup that has my highest Q tuning cap
and sitting just below the cap. So a short run. Hope to rectify* and
drive a voltmeter with some type of attenuator.
*Maybe even a peak detector.

If you build it, it'll be fun to hear what output voltage you get from
this stage when you drive your 0.3pF input cap with, say, 50mV AC. If
you put 50mV into the 0.3pF and get 25mV out the back end, that means
our net input capacitance after bootstrapping is about the same as your
series 0.3pF.

Cheers,
James Arthur

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

 

[bitrex]

On 03/20/2017 09:08 PM, Jim Thompson wrote:

On Tue, 14 Mar 2017 18:58:32 -0700, Jim Thompson
To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> 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

Well the docs tried to kill me, but I survived a very unpleasant trip.

They put a stent in my bile duct, but in recovery they discovered my
kidneys couldn't cope, and went into failure

So a one-day outpatient "procedure" ended up being a nasty 6-day
battle with helping the kidneys to recover.

Thanks to all for your good wishes!

...Jim Thompson

WB Jim, we have our, ah, "philosophical differences" but this NG
wouldn't be the same without you.

Who else would tell me my circuits were junk?

Don't answer that.

 

[amdx]

On 3/21/2017 9:57 AM, dagmargoodboat@yahoo.com wrote:

On Tuesday, March 21, 2017 at 8:54:35 AM UTC-4, amdx wrote:
On 3/20/2017 10:25 PM, rickman wrote:
On 3/20/2017 10:23 PM, amdx wrote:
On 3/20/2017 8:28 PM, rickman wrote:
On 3/20/2017 9:09 PM, amdx wrote:

I'm sure it could be built with a couple of opamps. It is a 50 ohm
output. Could probably do better, this starts to distort at I think
8 Vpp. But I don't have any antenna that need much that headroom.

That's 8Vpp open circuit, 4Vpp loaded.

Well then, eazy peazy. I used a circuit that used positive feedback to
make the output impedance look higher than the resistor in the circuit.
I think I used 12.5 or maybe it was just 12 and got multiplied by 4.
This makes the calculation of the gain a little more complex so you
would not be able to adjust the gain with a pot or anything... unless it
was on an earlier stage.

The middle stage with the single transistor, anything special about
that? It has a connection with caps I'm not familiar with from the
emitter to the input. That would be a low level of positive feedback I
believe. Any idea why?

He's bootstrapping the input impedance to avoid loading the FET stage.
Kleijer's crafty.

Hey I'm a semi-retired shrimp seller with a little bit of technical
skill. I did a good job of replicating the circuit, I didn't design it.
I can only explain operation on a simple level. If I had more knowledge
I would have corrected the distortion at increased input levels.
I suspect a good analog engineer would have done a lot of things
different to reach the goal of high input impedance, 50 ohm output. On
the other hand Kleijer built a working circuit and later went back and
built an improved second version. I follow the crystal radio community
and have not heard of anyone else that built the circuit, it's a shame
because it is a very useful piece of equipment for experimenting with
high Q LC circuits.

ISTM Kleijer did a very decent job, and got something more than good
enough for his task. And was nice enough to share it with everyone.
+1 for Kleijer.

I hope to take dagmar's design and improve it further.

We could do that, but it would add complexity without much benefit to
your application. Using an op-amp buffer instead of a BJT follower is
one possibility...

I worded that poorly, I meant, take dagmar's design to further improve
Kleijers design.
I hack, I don't design.
Mikek

Cheers,
James Arthur

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

 

[Kevin Aylward]

wrote in message news:shs0dcht0u1ueng46n19keljm5j7ienvpl@4ax.com...

On Mon, 20 Mar 2017 20:59:26 -0000, "Kevin Aylward"
<kevinRemovAT@kevinaylward.co.uk> wrote:

wrote in message news:2g6uccheh2pto7113hegrstud5ro8r8paj@4ax.com...

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.

Ok. After the Jury, judge and executioners have killed the aforementioned,
we can now kill said Jury, judge and executioners because they have now
killed someone, or taken deliberate action that resulted in the death of
someone. i.e. murdered someone.

It's obvious you're illiterate.

Its obvious that you can't understand the issues involved.

You have been brought up as a child that, if say, a judge, or the legal
system that you just happen to live in says its ok, than it is. I don't.

It is obviously way beyond you to understand that there is no essential
difference in one group with the biggest stick agreeing to kill someone,
then another.

So, yeah, further discussion is pointless.

-- Kevin Aylward
http://www.anasoft.co.uk - SuperSpice
http://www.kevinaylward.co.uk/ee/index.html

 

[rickman]

On 3/21/2017 8:54 AM, amdx wrote:

On 3/20/2017 10:25 PM, rickman wrote:
On 3/20/2017 10:23 PM, amdx wrote:
On 3/20/2017 8:28 PM, rickman wrote:
On 3/20/2017 9:09 PM, amdx wrote:
On 3/20/2017 7:55 PM, rickman wrote:
On 3/20/2017 6:54 PM, amdx wrote:
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.

I just meant it is small and I couldn't see what it was. Initially I
thought it might be a small value ceramic cap you put in place to
check
out the amp before you optimized the cap. Now I realize it is a very
small piece of PCB and *is* the optimized cap. I also didn't know
which
image was earlier and which was later.

Why would you adjust the overall circuit gain by trimming the cap?
The
amp gain can be trimmed, no?

I'm sure the amp can be changed, but the end game was to make the
input
cap small, I couldn't go much smaller.

What frequency range is this amp intended to be used for? Nearly all
the stuff I've seen where Q matters is LF or MF.

Kleijer says it's flat from 10kHz to 10 MHz.

They use loop antennas
for higher frequencies, but with too high Q the bandwidth gets so
narrow
even voice won't get through, just CW.

Most of the stuff I'm looking at is crystal radio, by the time you
start driving a headphone your Q gets lowered a lot. I never hear the
crystal radio guys complain about lack of bandwidth.

Some of the antennas Kleijer uses I would think would limit the
bandwidth of his circuits with Q of over 1000.

Again not a common problem, but easy to fix with a load resistor.

If the headphones or load resistor limit the Q, what is the bleeping
point of all that Litz wire and custom tuning capacitor stuff? I
thought the whole point was to get the Q as high as possible.

Yes, it is. But you still need to get the maximum power out to drive
your headphones.
In a perfect system, you would drop your Q by half to get maximum
audio. But the diode gets involved and that I can't decipher.


If you start with a Q over 1000 and end up with a few hundred, I
wouldn't
expect that to be distinguishable from a coil with a Q of some hundreds
which is where Kleijer started in his coil investigations.

This is radio dxing, grab every db of signal!


If the frequencies are not so high, why not use an opamp for the
final
stage rather than the much more complex push-pull stage? I assume
that
is intended to be in essence a "power" output stage and does not
otherwise contribute significantly to the characteristics of the
rest of
the circuit.

I'm sure it could be built with a couple of opamps. It is a 50 ohm
output. Could probably do better, this starts to distort at I think
8 Vpp. But I don't have any antenna that need much that headroom.

That's 8Vpp open circuit, 4Vpp loaded.

Well then, eazy peazy. I used a circuit that used positive feedback to
make the output impedance look higher than the resistor in the circuit.
I think I used 12.5 or maybe it was just 12 and got multiplied by 4.
This makes the calculation of the gain a little more complex so you
would not be able to adjust the gain with a pot or anything... unless it
was on an earlier stage.

The middle stage with the single transistor, anything special about
that? It has a connection with caps I'm not familiar with from the
emitter to the input. That would be a low level of positive feedback I
believe. Any idea why?

Hey I'm a semi-retired shrimp seller with a little bit of technical
skill. I did a good job of replicating the circuit, I didn't design it.
I can only explain operation on a simple level. If I had more knowledge
I would have corrected the distortion at increased input levels.
I suspect a good analog engineer would have done a lot of things
different to reach the goal of high input impedance, 50 ohm output. On
the other hand Kleijer built a working circuit and later went back and
built an improved second version. I follow the crystal radio community
and have not heard of anyone else that built the circuit, it's a shame
because it is a very useful piece of equipment for experimenting with
high Q LC circuits.
I hope to take dagmar's design and improve it further.


I designed an opamp circuit to output an 8 volt signal with a 12 volt
supply into 50 ohm cable. I didn't quite get 8 volts before it starts
to distort, but it was close. I believe the gain-bandwidth product of
the amp was over 30 MHz, so it should do ok at 10 MHz and no gain. But
then you need a little gain I guess. Opps, no, the GB was 15 MHz.

Wait a minute!!! That bootstrap of the input resistors won't work. The
470 ohm source resistor is there to set a bias point with the source
higher than the gate. The resistors are there to set the DC voltage of
the gate to ground. Perhaps a cap could be used to feed the point
between the two resistors?

I just realized that is the purpose of the two caps on T2 emitter to the
47 ohm resistor. It allows the resistors to set the DC operating point
but bootstraps their capacitance. No?

??
I have looked for a data sheet on the BF256C, all I can find is very
limited info, Anyone find a data sheet with the device capacitances?

NXP says the BF245C is the same as (or a replacement for) the BF256C.
Here is a data sheet, pretty complete.

http://www.nxp.com/documents/data_sheet/BF245A-B-C.pdf

--

Rick C