High Q smd capacitors

[piglet]

On 26/07/2019 1:42 am, amdx wrote:

On 7/25/2019 2:40 PM, upsidedown@downunder.com wrote:
On Thu, 25 Jul 2019 13:10:47 -0500, amdx <nojunk@knology.net> wrote:


  In one of my posts, I mentioned that someone is putting together a
ring down Q meter and trying to save a few bucks going with high Q smd
vs a good variable air cap. This is crystal radio stuff and Qs can get
as high as 1500. So, in order to improve accuracy I expect the best cap
at a reasonable price. But I would hope it is 10x higher Q than the
highest
Q coil to be measured. Even with that, it would still measure the coil Q
down my 10%. (I didn't run the numbers, but it's close)

So this is for a crystal set for receiving AM broadcasts in the 0.5 -
1,5 MHz band ? For AM reception, the detector needs the carrier and at
least of one sideband.  Assuming 5 kHz required bandwidth, that will
required loaded Ql at the low end of the band of 100 and 300 at the
top of the band.


 I was a little surprised with the 100 and 300. But I can see the
advantage of having a high Q LC is that you can
extra more audio from the recovered signal. Thus on a DX weak signal
you can hear it because you started with high Q front end.
 The DX contest winners aren't #20 wire on a cardboard tube, they go
all out to minimize losses.


On the other hand, the unloaded Qu should be a few times larger than
the loaded Ql in order to minimize passband insertion losses. The
insertion loss is given by

     Loss_dB  = 20 log (1/ (1-Ql/Qu) )

Assuming (unrealistically) that Qu remains at 1500 all over the band.
Thus at the low end of the band the insertion loss is 0.6 dB and at
1.5 MHz 1.9 dB. A 10 % error in the Qu measurement doesn't affect the
insertion loss very much.

Just out of curiosity - do you crystal radio folk ever use double tuned
(aka stagger tuned) high Q tuned circuits? That may keep the steep
slopes of hi-Q but a broader passband to more faithfully pass audio
modulation. My last crystal radio was 1967 so I am out of touch.

piglet

 

[Michael Terrell]

On Friday, July 26, 2019 at 2:35:19 AM UTC-4, piglet wrote:

Just out of curiosity - do you crystal radio folk ever use double tuned
(aka stagger tuned) high Q tuned circuits? That may keep the steep
slopes of hi-Q but a broader passband to more faithfully pass audio
modulation. My last crystal radio was 1967 so I am out of touch.

People who 'restore' old radios insist on tuning the IF stages for peak gain, then complain about poor audio. I've tried to explain how to tune for good gain and audio, but they replace parts, and misalign them. I would rather lose about 1 dB and have better audio. I built an outboard adapter for a tighter IF that someone wanted. It was so narrow that I added resistors across each tuned circuit to lower the Q slightly. (I was a kid, and had no signal generator to do a proper alignment.) Even then, it was about 3.5 KHz recovered audio but it was a lot quieter for DX reception. I think Hams called it a 'Q5'?

 

[amdx]

On 7/26/2019 1:35 AM, piglet wrote:

On 26/07/2019 1:42 am, amdx wrote:
On 7/25/2019 2:40 PM, upsidedown@downunder.com wrote:
On Thu, 25 Jul 2019 13:10:47 -0500, amdx <nojunk@knology.net> wrote:


  In one of my posts, I mentioned that someone is putting together a
ring down Q meter and trying to save a few bucks going with high Q smd
vs a good variable air cap. This is crystal radio stuff and Qs can get
as high as 1500. So, in order to improve accuracy I expect the best cap
at a reasonable price. But I would hope it is 10x higher Q than the
highest
Q coil to be measured. Even with that, it would still measure the
coil Q
down my 10%. (I didn't run the numbers, but it's close)

So this is for a crystal set for receiving AM broadcasts in the 0.5 -
1,5 MHz band ? For AM reception, the detector needs the carrier and at
least of one sideband.  Assuming 5 kHz required bandwidth, that will
required loaded Ql at the low end of the band of 100 and 300 at the
top of the band.


  I was a little surprised with the 100 and 300. But I can see the
advantage of having a high Q LC is that you can
extra more audio from the recovered signal. Thus on a DX weak signal
you can hear it because you started with high Q front end.
  The DX contest winners aren't #20 wire on a cardboard tube, they go
all out to minimize losses.


On the other hand, the unloaded Qu should be a few times larger than
the loaded Ql in order to minimize passband insertion losses. The
insertion loss is given by

     Loss_dB  = 20 log (1/ (1-Ql/Qu) )

Assuming (unrealistically) that Qu remains at 1500 all over the band.
Thus at the low end of the band the insertion loss is 0.6 dB and at
1.5 MHz 1.9 dB. A 10 % error in the Qu measurement doesn't affect the
insertion loss very much.



Just out of curiosity - do you crystal radio folk ever use double tuned
(aka stagger tuned) high Q tuned circuits? That may keep the steep
slopes of hi-Q but a broader passband to more faithfully pass audio
modulation. My last crystal radio was 1967 so I am out of touch.

piglet

I'm far from an an expert, I just enjoy reading the crystal radio
forum, (since 2010). >
http://theradioboard.com/rb/viewforum.php?f=2&sid=00da6d09624871e21366fa901bfd7401
There are plenty of double tuned circuits,
Ithink this is fairly high end, > http://makearadio.com/crystal/69.php

Here's a URL with 78 well done crystal radios.

http://makearadio.com/crystal/index.php

Mikek

 

On Fri, 26 Jul 2019 07:35:12 +0100, piglet <erichpwagner@hotmail.com>
wrote:

Just out of curiosity - do you crystal radio folk ever use double tuned
(aka stagger tuned) high Q tuned circuits? That may keep the steep
slopes of hi-Q but a broader passband to more faithfully pass audio
modulation. My last crystal radio was 1967 so I am out of touch.

There are two ways of broadening the pass band width while still
maintaining good skirts in a double tuned circuit.

One is stagger tuning, i.e. the resonant circuits are tuned at
slightly different frequencies.

The other is varying the coupling between to circuits tuned at the
same frequency. With a very light coupling, the response becomes
peaky. When increasing the coupling, the pass band flattens. With very
tight coupling between the resonance circuits, you finally get a
double hump response.

 

[amdx]

On 7/25/2019 1:52 PM, Jeff Liebermann wrote:

On Thu, 25 Jul 2019 13:10:47 -0500, amdx <nojunk@knology.net> wrote:

In one of my posts, I mentioned that someone is putting together a
ring down Q meter and trying to save a few bucks going with high Q smd
vs a good variable air cap. This is crystal radio stuff and Qs can get
as high as 1500.

How does that work? The upper modulation frequency of BCB AM is
10.2KHz yielding an occupied bandwidth of about 20.4KHz. At 1MHz and
a Q=1500, the 3dB bandwidth of the LC circuit is:
1MHz / 1500 = 670 Hz
That's narrower than the AM occupied bandwidth, so the high frequency
audio will not pass. Probably great for CW or 160 meters, but nobody
does CW on the broadcast band.

The Q=1500 might be the unloaded Q as the diode detector forward
conduction resistance does present a rather low resistance in parallel
with at least part of the LC circuit. To get all the audio
frequencies through, the maximum loaded Q is:
1MHz / 20.4KHz = 49
http://www.sengpielaudio.com/calculator-cutoffFrequencies.htm

Incidentally, I run into the same problem with small loop antennas
also known as magnetic loop, where the antenna Q becomes sufficiently
high that only the lower audio frequencies are passed. The resulting
audio sounds "muffled". It's possible to build very high Q loop
antennas that are useless.
"Small Transmitting Loop Antennas"
http://www.aa5tb.com/loop.html
http://www.aa5tb.com/aa5tb_loop_v1.22e.xlsx

So, in order to improve accuracy I expect the best cap
at a reasonable price. But I would hope it is 10x higher Q than the highest
Q coil to be measured. Even with that, it would still measure the coil Q
down my 10%. (I didn't run the numbers, but it's close)

10 times higher Q for the capacitors in the instrument sounds about
right, but you could probably survive with less. I'm not familiar
with a ring down Q meter, so I don't know exactly what's required.

Here's video with a little info about the ring down counter.
I suspect you would figure it out but I'll get you started, it counts
oscillations after drive is removed, down to a certain percentage of the
original amplitude. From the little I see, I think the input impedance
(loading) during ring down it to low for a high Q measurement to be
accurate. But the schematic is hard to read.

https://www.youtube.com/watch?v=ImB3cZOggeY&feature=youtu.be
Don't watch more that 4 minutes.

Mikke

 

[Jeff Liebermann]

On Sun, 28 Jul 2019 12:11:20 -0500, amdx <nojunk@knology.net> wrote:

Here's video with a little info about the ring down counter.
I suspect you would figure it out but I'll get you started, it counts
oscillations after drive is removed, down to a certain percentage of the
original amplitude.

Oh. I was thinking hybrid ring, ring oscillator, Token Ring,
tinnitus, Saturn's rings, etc.

From the little I see, I think the input impedance
(loading) during ring down it to low for a high Q measurement to be
accurate. But the schematic is hard to read.

The Q values shown on the LCD display were rather low. Q=550 was the
highest I saw (at the end). He was using the same ferrite core, which
would not have yield a very high Q. Air cores would have been more
interesting.

You keep switching back and forth between unloaded Q and loaded Q.
Unloaded Q is just the L-C part of the crystal radio. Loaded Q
include the antenna, diode detector, and whatever else is connected to
the L-C circuit. Unloaded Q is always larger than loaded Q. If
you're measuring the unloaded Q with various instruments and
techniques, you're not getting the operational parameters. For
example, my estimate of the unloaded Q as being narrower than the
modulation bandwidth is obviously not correct because it is possible
to hear AM stations with reasonable fidelity. That's because the
antenna, diode, etc are adding losses across the L-C circuit and
reducing its Q. The lower Q results in wider receiver bandwidth which
not passes the higher audio frequencies. I suggest that when you
mention the Q of a circuit, you specify whether you're talking about
unloaded or loaded Q.

Incidentally, unloaded Q is usually measured with test equipment,
usually an RLC meter/bridge, or the aforementioned ring down detector.
Loaded Q is measured with an RF signal/sweep generator and an RF
voltmeter or spectrum analyzer looking at the -3dB points and
specified as the RF/IF bandwidth.

I skimmed through the various crystal radio project pages at:
<http://www.crystalradio.net>
<http://www.crystalradio.net/links.shtml>
There were far too many examples for me to skim them all. However, I
noticed the absence of conventional AM SINAD sensitivity, IMD, dynamic
range, modulation acceptance bandwidth, etc measurements. (1KHz tone,
30% modulation, 12dB SINAD, at >50% of rated audio output). These
tests appear for every manner of tube, valve, and transistor receiver,
by not crystal radios. I can see that there might be a problem
matching the antenna input to the signal generator 50 ohm output, but
that can always be done with a very lossy resistive pad. I found
plenty of articles mumbling something about high sensitivity crystal
radio, but no measurements. Am I missing something obvious here?

https://www.youtube.com/watch?v=ImB3cZOggeY&feature=youtu.be
Don't watch more that 4 minutes.

Thanks. I fell asleep a little after 6 minutes. It eventually became
clear that he was testing various variable capacitors to see which
offered the best Q. However, no numbers, results, or clues as to what
he was testing. It might have been interesting if he measured all the
variable caps at the same frequency and recorded the measured Q.




--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[amdx]

On 7/28/2019 7:12 PM, Jeff Liebermann wrote:

On Sun, 28 Jul 2019 12:11:20 -0500, amdx <nojunk@knology.net> wrote:

Here's video with a little info about the ring down counter.
I suspect you would figure it out but I'll get you started, it counts
oscillations after drive is removed, down to a certain percentage of the
original amplitude.

Oh. I was thinking hybrid ring, ring oscillator, Token Ring,
tinnitus, Saturn's rings, etc.

From the little I see, I think the input impedance
(loading) during ring down it to low for a high Q measurement to be
accurate. But the schematic is hard to read.

The Q values shown on the LCD display were rather low. Q=550 was the
highest I saw (at the end). He was using the same ferrite core, which
would not have yield a very high Q. Air cores would have been more
interesting.

There is very high Q ferrite that the enthusiasts are using and
getting Qs in the 1200 to 1400 range. (BCB) And because I know who the
author is, I'm pretty sure he is using that ferrite.

You keep switching back and forth between unloaded Q and loaded Q.

Well not really, I'm really only interested in unloaded Q. I'm talking
about a tool to measure Q of a coil and maybe cap. If I were building it
I wouldn't put a 500k resistor across my LC and then try to measure the
Q of the LC.

> Unloaded Q is just the L-C part of the crystal radio.
Absolutely, but it is an important part and usually where the build
starts. You won't have a high end crystal radio if you don't start with
a high Q coil and cap.

Loaded Q
include the antenna, diode detector, and whatever else is connected to
the L-C circuit. Unloaded Q is always larger than loaded Q. If
you're measuring the unloaded Q with various instruments and
techniques, you're not getting the operational parameters. For
example, my estimate of the unloaded Q as being narrower than the
modulation bandwidth is obviously not correct because it is possible
to hear AM stations with reasonable fidelity. That's because the
antenna, diode, etc are adding losses across the L-C circuit and
reducing its Q. The lower Q results in wider receiver bandwidth which
not passes the higher audio frequencies. I suggest that when you
mention the Q of a circuit, you specify whether you're talking about
unloaded or loaded Q.

I'm talking about measuring the Q of a coil, I kinda have to use
either my experience or someone else's to inform me if an air cap is a
good air cap or not. More difficult to measure but you can compare caps
if you have a good coil and an instrument with a high input impedance.
Looking at the Boonton 260A manual page 14, it shows about 15Mohms of
input resistance at 1MHz.

http://hparchive.com/Boonton/Boonton-Manual-260A.pdf

Incidentally, unloaded Q is usually measured with test equipment,
usually an RLC meter/bridge, or the aforementioned ring down detector.
Loaded Q is measured with an RF signal/sweep generator and an RF
voltmeter or spectrum analyzer looking at the -3dB points and
specified as the RF/IF bandwidth.

Yes, that can be done, I don't see a lot of discussion about
measuring the Q of a completed crystal radio system.

I skimmed through the various crystal radio project pages at:
http://www.crystalradio.net
http://www.crystalradio.net/links.shtml
There were far too many examples for me to skim them all. However, I
noticed the absence of conventional AM SINAD sensitivity, IMD, dynamic
range, modulation acceptance bandwidth, etc measurements. (1KHz tone,
30% modulation, 12dB SINAD, at >50% of rated audio output). These
tests appear for every manner of tube, valve, and transistor receiver,
by not crystal radios. I can see that there might be a problem
matching the antenna input to the signal generator 50 ohm output, but
that can always be done with a very lossy resistive pad. I found
plenty of articles mumbling something about high sensitivity crystal
radio, but no measurements. Am I missing something obvious here?

No, I don't think you are missing it, as I say I don't think much of
that type work is done. Most people make a good LC, try to find a diode
that matches the high impedance and then use an audio transformer to
match a good set of sound powered phones (often old deck talker
headphones). Then all goes to hell depending on signal strength. So then
they switch in different diodes and have multiple taps on the audio
transformer. Also variable coupling if using a double tuned system.
And every thing is designed to minimize loss, note in the Ringdown
video, he gets distance from lossy items by a layer of styrofoam.
It seems we have been in this discussion before, but a real guru in
this was Ben Tongue of Blonder-Tongue fame. He wrote many pages with
lots of research into crystal radio design.
> http://www.bentongue.com/category/crystal-radio-set-design/
He has died and the look of the page was changed, but I think it's all
there.
Here's the original from the Wayback machine.
> https://web.archive.org/web/20101119110829/http://bentongue.com/xtalset/xtalset.html

I like the old presentation better. Be forewarned, there is a month of
information here.

https://www.youtube.com/watch?v=ImB3cZOggeY&feature=youtu.be
Don't watch more that 4 minutes.

Thanks. I fell asleep a little after 6 minutes. It eventually became
clear that he was testing various variable capacitors to see which
offered the best Q. However, no numbers, results, or clues as to what
he was testing. It might have been interesting if he measured all the
variable caps at the same frequency and recorded the measured Q.

I almost bitched to him about that same thing, but instead ask for
the value of the input resistors.
Mikek

 

[Jeff Liebermann]

On Sun, 28 Jul 2019 20:38:40 -0500, amdx <nojunk@knology.net> wrote:

Well not really, I'm really only interested in unloaded Q. I'm talking
about a tool to measure Q of a coil and maybe cap. If I were building it
I wouldn't put a 500k resistor across my LC and then try to measure the
Q of the LC.

From one of Ben Tongue's articles that you referenced:
<https://web.archive.org/web/20101119112253/http://bentongue.com/xtalset/24Cmnts/24Cmnts.html>
Table 2 shows that the ratio of loaded to unloaded Q (QI/Qo) varies
from 0.1 to 0.6 depending on matching. Since the unloaded Q is always
higher than the loaded Q, I would deduce from Table 2 that
improvements in unloaded Q are not going to make much of an overall
improvement. Methinks that experimentation with better antennas,
diodes and impedance matching might yield better results.

Unloaded Q is just the L-C part of the crystal radio.
Absolutely, but it is an important part and usually where the build
starts. You won't have a high end crystal radio if you don't start with
a high Q coil and cap.

Fine. So use a tapped spiral wound air core loop inductor as a
combination antenna and L-C inductor and be done with the L-C part of
the design. It would be difficult to do better than that for the L-C
part. Increasing the unloaded Q, while seemingly ignoring the loading
components, is not going to make any major improvements. Worse, if
you actually succeed in making a major improvement in reducing the
reduction in Q caused by the diode, you run the risk of ending up with
a receive with too little bandwidth (as previously described).

I'm talking about measuring the Q of a coil, I kinda have to use
either my experience or someone else's to inform me if an air cap is a
good air cap or not. More difficult to measure but you can compare caps
if you have a good coil and an instrument with a high input impedance.
Looking at the Boonton 260A manual page 14, it shows about 15Mohms of
input resistance at 1MHz.
http://hparchive.com/Boonton/Boonton-Manual-260A.pdf

The Boonton 260A maxes out at Q=625.
The HP4342A was my Q meter of choice during the 1970's with a maximum
Q=1000.
<https://www.google.com/search?q=hp+4342a&tbm=isch>
<http://www.libertytest.com/assetmanager/uploaded/pdf-201046-12916-hp_4342a.pdf>
I also worked with a Heathkit QM-1 Q meter which had a maximum Q=250.
<https://www.google.com/search?tbm=isch&q=heathkit+q+meter>
Today, we have the HP-4191 Impedance Analyzer. Maximum (calculated)
Q=1000.
<https://www.w8ji.com/loading_inductors.htm>
I've found it difficult here to get perfectly repeatable
measurements even using expensive laboratory equipment.
For example I use a HP-4191A Impedance Analyzer. I still
cross check inductors by placing them in a large copper-lined
box and tune them to resonance with vacuum variables (Q>50,000).
By measuring inductor current and voltage across the vacuum
variable, or measuring the series or parallel RF resistance,
I can determine Q or ESR.
The highest Q I have found is around 1000 or just over 1000
when determining Q by using X / ESR = Q.

Yes, that can be done, I don't see a lot of discussion about
measuring the Q of a completed crystal radio system.

Sweep the receiver and measure the output voltage below and above the
center frequency peak. When the voltage drops to 0.707 times the peak
voltage, you have the -3dB power point. The difference in the two
frequencies is the bandwidth. Divide the center frequency by the
bandwidth and you have the receiver loaded Q.
<http://www.sengpielaudio.com/calculator-cutoffFrequencies.htm>

It seems we have been in this discussion before, but a real guru in
this was Ben Tongue of Blonder-Tongue fame. He wrote many pages with
lots of research into crystal radio design.
http://www.bentongue.com/category/crystal-radio-set-design/
He has died and the look of the page was changed, but I think it's all
there.
Here's the original from the Wayback machine.
https://web.archive.org/web/20101119110829/http://bentongue.com/xtalset/xtalset.html

I like the old presentation better. Be forewarned, there is a month of
information here.

I agree. The old web pages are better and easier to read.

Drivel: I find it rather amusing that some web designers try to
emulate the look of newspaper columns. Such columns were originally
invented because movable type was difficult to align in a straight
line across the page. By cutting the width of the page into columns,
the wandering lines of type were less visible. Like the typewriter
keyboard, these problems were solved long ago, but we're stuck with
the band-aids to this day. Sigh.

I almost bitched to him about that same thing, but instead ask for
the value of the input resistors.

Perhaps I'm overly paranoid, but when I see important numbers and
measurements missing, I tend to suspect that they're hiding something.
Also, it's really difficult to determine if you're making progress
without such measurements (or comparison to a known reference). How
do you know that a receiver is "high sensitivity" if nobody bothers to
make the measurements? I can't even find graphs for the audio
frequency response or dynamic range (which I suspect sucks).

"Testing Crystal Radio Reception"
<https://www.antiqueradios.com/forums/viewtopic.php?f=2&t=234777>
The strength could be assessed with a sensitive voltmeter.
Most stations will generate only millivolts of signal. You
might try hooking a cheap digital voltmeter across the
headphone connection.

Sigh...


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[amdx]

On 7/29/2019 12:56 AM, Jeff Liebermann wrote:

On Sun, 28 Jul 2019 20:38:40 -0500, amdx <nojunk@knology.net> wrote:

Well not really, I'm really only interested in unloaded Q. I'm talking
about a tool to measure Q of a coil and maybe cap. If I were building it
I wouldn't put a 500k resistor across my LC and then try to measure the
Q of the LC.

From one of Ben Tongue's articles that you referenced:
https://web.archive.org/web/20101119112253/http://bentongue.com/xtalset/24Cmnts/24Cmnts.html
Table 2 shows that the ratio of loaded to unloaded Q (QI/Qo) varies
from 0.1 to 0.6 depending on matching. Since the unloaded Q is always
higher than the loaded Q, I would deduce from Table 2 that
improvements in unloaded Q are not going to make much of an overall
improvement. Methinks that experimentation with better antennas,
diodes and impedance matching might yield better results.

We can disagree, but it seems, if I build a coil with a Q of 1200 at
1MHz and load it to say 0.35, picking the middle of the range suggested.
The loaded Q would be 420. Vs. building a coil with Q = 600 loaded at
0.35, now my loaded Q is 210. I think doubling Q is worthwhile. I'm out
on a limb on my next statement, I also think, with the lower Q I may try
to load it a little more to get a higher audio level if I can't here it.
And to add, with the higher Q coil, I could load it a little less and
still have enough audio.
As with many pursuits, you try to optimize the results for the least
dollars, and then there are a few that will optimize regardless of cost.
And yes, if you are trying to build a high end crystal radio, you will
optimize more than just the LC, and yes there are well known diodes that
are better for high end crystal radios, (FO215).
But the optimum diode is picked for the situation,RE:LC impedance and
signal strength.

Before I lose your interest, I did find a better schematic of the
ringdown Q meter. >
http://www.crystalradio.cn/data/attachment/forum/201806/23/095734cnoor5w1z9zwkf61.png
The resistors are 5.6Mohm, so higher than I though I could see on the
poor res pic. Also those 5.6Mohm are isolated by a 3.3pf capacitor.
Note there is back biased diode, not sure what load that is.
The front end is similar to the Kleijer amp (version 2) I built a
while back.

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

Unloaded Q is just the L-C part of the crystal radio.
Absolutely, but it is an important part and usually where the build
starts. You won't have a high end crystal radio if you don't start with
a high Q coil and cap.

Fine. So use a tapped spiral wound air core loop inductor as a
combination antenna and L-C inductor and be done with the L-C part of
the design. It would be difficult to do better than that for the L-C
part. Increasing the unloaded Q, while seemingly ignoring the loading
components, is not going to make any major improvements. Worse, if
you actually succeed in making a major improvement in reducing the
reduction in Q caused by the diode, you run the risk of ending up with
a receive with too little bandwidth (as previously described).

People do make larger air core inductors as the antenna and the L in
the LC circuit. But for long distance reception you need a long wire
antenna.

I'm talking about measuring the Q of a coil, I kinda have to use
either my experience or someone else's to inform me if an air cap is a
good air cap or not. More difficult to measure but you can compare caps
if you have a good coil and an instrument with a high input impedance.
Looking at the Boonton 260A manual page 14, it shows about 15Mohms of
input resistance at 1MHz.
http://hparchive.com/Boonton/Boonton-Manual-260A.pdf

The Boonton 260A maxes out at Q=625.

Yes, I spent does trying to find a way to measure higher Qs with it.
You can measure higher Qs with a 260A. The normal injection voltage is
20mV, if you lower the injection voltage to 5mV you can measure up to
1000, 2mV, up to 2500. But it requires a sensitive voltmeter and voddoo
to rid the area of the evils of measuring small voltages accurately.

The HP4342A was my Q meter of choice during the 1970's with a maximum
Q=1000.
https://www.google.com/search?q=hp+4342a&tbm=isch
http://www.libertytest.com/assetmanager/uploaded/pdf-201046-12916-hp_4342a.pdf
I also worked with a Heathkit QM-1 Q meter which had a maximum Q=250.
https://www.google.com/search?tbm=isch&q=heathkit+q+meter
Today, we have the HP-4191 Impedance Analyzer. Maximum (calculated)
Q=1000.
https://www.w8ji.com/loading_inductors.htm
I've found it difficult here to get perfectly repeatable
measurements even using expensive laboratory equipment.
For example I use a HP-4191A Impedance Analyzer. I still
cross check inductors by placing them in a large copper-lined
box and tune them to resonance with vacuum variables (Q>50,000).
By measuring inductor current and voltage across the vacuum
variable, or measuring the series or parallel RF resistance,
I can determine Q or ESR.
The highest Q I have found is around 1000 or just over 1000
when determining Q by using X / ESR = Q.

Yes, that can be done, I don't see a lot of discussion about
measuring the Q of a completed crystal radio system.

Yep, there is discussion of repeatability of high Q measurements,
we just do the best we can. In the experiment I did with 5 coils of
differing turns per inch, I did three measurements and averaged.

Sweep the receiver and measure the output voltage below and above the
center frequency peak. When the voltage drops to 0.707 times the peak
voltage, you have the -3dB power point. The difference in the two
frequencies is the bandwidth. Divide the center frequency by the
bandwidth and you have the receiver loaded Q.
http://www.sengpielaudio.com/calculator-cutoffFrequencies.htm

Dave of proficient builder did a bandwidth study here.

http://makearadio.com/misc-stuff/bandwidth.php

It seems we have been in this discussion before, but a real guru in
this was Ben Tongue of Blonder-Tongue fame. He wrote many pages with
lots of research into crystal radio design.
http://www.bentongue.com/category/crystal-radio-set-design/
He has died and the look of the page was changed, but I think it's all
there.
Here's the original from the Wayback machine.
https://web.archive.org/web/20101119110829/http://bentongue.com/xtalset/xtalset.html

I like the old presentation better. Be forewarned, there is a month of
information here.

I agree. The old web pages are better and easier to read.

Drivel: I find it rather amusing that some web designers try to
emulate the look of newspaper columns. Such columns were originally
invented because movable type was difficult to align in a straight
line across the page. By cutting the width of the page into columns,
the wandering lines of type were less visible. Like the typewriter
keyboard, these problems were solved long ago, but we're stuck with
the band-aids to this day. Sigh.

I almost bitched to him about that same thing, but instead ask for
the value of the input resistors.

Perhaps I'm overly paranoid, but when I see important numbers and
measurements missing, I tend to suspect that they're hiding something.
Also, it's really difficult to determine if you're making progress
without such measurements (or comparison to a known reference). How
do you know that a receiver is "high sensitivity" if nobody bothers to
make the measurements? I can't even find graphs for the audio
frequency response or dynamic range (which I suspect sucks).

Ya, I don't know what that was all about, ay be he was just showing
what he was going to do, or maybe he just clipped a bunch of nibblets of
his tests. That poster is a very busy builder and comes up with unique
crystal radios, nothing I would say is "very high end", but some really
neat stuff.

"Testing Crystal Radio Reception"
https://www.antiqueradios.com/forums/viewtopic.php?f=2&t=234777
The strength could be assessed with a sensitive voltmeter.
Most stations will generate only millivolts of signal. You
might try hooking a cheap digital voltmeter across the
headphone connection.

Sigh...

There are many crystal radios the employ a meter to see signal strength.

http://crystal-radio.weebly.com/crystal-set-with-an-output-meter.html
http://www.crystalradio.net/contest/paul.html

There are more, I'm just lazy.

Mikek

 

On Mon, 29 Jul 2019 11:28:27 -0500, amdx <nojunk@knology.net> wrote:

On 7/29/2019 12:56 AM, Jeff Liebermann wrote:
On Sun, 28 Jul 2019 20:38:40 -0500, amdx <nojunk@knology.net> wrote:

Well not really, I'm really only interested in unloaded Q. I'm talking
about a tool to measure Q of a coil and maybe cap. If I were building it
I wouldn't put a 500k resistor across my LC and then try to measure the
Q of the LC.

From one of Ben Tongue's articles that you referenced:
https://web.archive.org/web/20101119112253/http://bentongue.com/xtalset/24Cmnts/24Cmnts.html
Table 2 shows that the ratio of loaded to unloaded Q (QI/Qo) varies
from 0.1 to 0.6 depending on matching. Since the unloaded Q is always
higher than the loaded Q, I would deduce from Table 2 that
improvements in unloaded Q are not going to make much of an overall
improvement. Methinks that experimentation with better antennas,
diodes and impedance matching might yield better results.

We can disagree, but it seems, if I build a coil with a Q of 1200 at
1MHz and load it to say 0.35, picking the middle of the range suggested.
The loaded Q would be 420. Vs. building a coil with Q = 600 loaded at
0.35, now my loaded Q is 210.

Load it with 0.7 and you will get the same loaded Q and hence
bandwidth.

I think doubling Q is worthwhile. I'm out
on a limb on my next statement, I also think, with the lower Q I may try
to load it a little more to get a higher audio level if I can't here it.
And to add, with the higher Q coil, I could load it a little less and
still have enough audio.

The losses at 0.35 is about 5 dB, but at 0.7 maybe 9 dB, so the
recovered audio would be down by 4 dB. Is this too much, it is up to
you to decide.

A decent antenna is very important with passive receivers. A short
vertical has nearly the same capture area as a full sized 1/4 wave
vertical antenna. The nasty thing with electrically short antennas is
that they have strong capacitive reactance and a radiation resistance
of perhaps only a few ohms (insteead of nominal 37 ohms of a 1/4 sized
antenna). The problem is getting all the captured power into yor LC
circuit.

There are several tricks to do this. Adding a top hat dcapacitanse to
your short vertical will help a lot. A T-antenna or Z-top hat
capacitance are often used. A series loading coil can be used to tune
out the antenna capacitive reactance. Now you have a resistive
impedance of a few ohms. Feed the antenna to a tap very close to
ground of your LC coil or use a few turn primary to perform the
impedance matching.
.

The other way of looking at short verticals is to talk about effective
heights, which is close to 1/4 wavelength even for a short antenna.
If the field strength [V/m] is known, then you can calculate the
signal voltage into a full sized vertical. To calculate what the short
antenna vill produce, you must include the impedance ratios.

 

[amdx]

On 7/29/2019 12:23 PM, upsidedown@downunder.com wrote:

On Mon, 29 Jul 2019 11:28:27 -0500, amdx <nojunk@knology.net> wrote:

On 7/29/2019 12:56 AM, Jeff Liebermann wrote:
On Sun, 28 Jul 2019 20:38:40 -0500, amdx <nojunk@knology.net> wrote:

Well not really, I'm really only interested in unloaded Q. I'm talking
about a tool to measure Q of a coil and maybe cap. If I were building it
I wouldn't put a 500k resistor across my LC and then try to measure the
Q of the LC.

From one of Ben Tongue's articles that you referenced:
https://web.archive.org/web/20101119112253/http://bentongue.com/xtalset/24Cmnts/24Cmnts.html
Table 2 shows that the ratio of loaded to unloaded Q (QI/Qo) varies
from 0.1 to 0.6 depending on matching. Since the unloaded Q is always
higher than the loaded Q, I would deduce from Table 2 that
improvements in unloaded Q are not going to make much of an overall
improvement. Methinks that experimentation with better antennas,
diodes and impedance matching might yield better results.

We can disagree, but it seems, if I build a coil with a Q of 1200 at
1MHz and load it to say 0.35, picking the middle of the range suggested.
The loaded Q would be 420. Vs. building a coil with Q = 600 loaded at
0.35, now my loaded Q is 210.

Load it with 0.7 and you will get the same loaded Q and hence
bandwidth.

And less audio signal. Audio is low enough, no need to start with a
poor LC.

I think doubling Q is worthwhile. I'm out
on a limb on my next statement, I also think, with the lower Q I may try
to load it a little more to get a higher audio level if I can't here it.
And to add, with the higher Q coil, I could load it a little less and
still have enough audio.

The losses at 0.35 is about 5 dB, but at 0.7 maybe 9 dB, so the
recovered audio would be down by 4 dB. Is this too much, it is up to
you to decide.

Oh, looks like you knew about less audio.

A decent antenna is very important with passive receivers. A short
vertical has nearly the same capture area as a full sized 1/4 wave
vertical antenna. The nasty thing with electrically short antennas is
that they have strong capacitive reactance and a radiation resistance
of perhaps only a few ohms (insteead of nominal 37 ohms of a 1/4 sized
antenna). The problem is getting all the captured power into yor LC
circuit.

There are several tricks to do this. Adding a top hat dcapacitanse to
your short vertical will help a lot. A T-antenna or Z-top hat
capacitance are often used. A series loading coil can be used to tune
out the antenna capacitive reactance. Now you have a resistive
impedance of a few ohms. Feed the antenna to a tap very close to
ground of your LC coil or use a few turn primary to perform the
impedance matching.
.

The other way of looking at short verticals is to talk about effective
heights, which is close to 1/4 wavelength even for a short antenna.
If the field strength [V/m] is known, then you can calculate the
signal voltage into a full sized vertical. To calculate what the short
antenna vill produce, you must include the impedance ratios.

First I've heard about verticals discussed with crystal radios.
Can't add anything.
Here's what Ben Tongue had to say about long wire characteristics.
> https://web.archive.org/web/20131030052147/http://www.bentongue.com/xtalset/20MeaAGs/20MeaAGs.html

Mikek

 

On Mon, 29 Jul 2019 14:39:49 -0500, amdx <nojunk@knology.net> wrote:

A decent antenna is very important with passive receivers. A short
vertical has nearly the same capture area as a full sized 1/4 wave
vertical antenna. The nasty thing with electrically short antennas is
that they have strong capacitive reactance and a radiation resistance
of perhaps only a few ohms (insteead of nominal 37 ohms of a 1/4 sized
antenna). The problem is getting all the captured power into yor LC
circuit.

There are several tricks to do this. Adding a top hat dcapacitanse to
your short vertical will help a lot. A T-antenna or Z-top hat
capacitance are often used. A series loading coil can be used to tune
out the antenna capacitive reactance. Now you have a resistive
impedance of a few ohms. Feed the antenna to a tap very close to
ground of your LC coil or use a few turn primary to perform the
impedance matching.
.

The other way of looking at short verticals is to talk about effective
heights, which is close to 1/4 wavelength even for a short antenna.
If the field strength [V/m] is known, then you can calculate the
signal voltage into a full sized vertical. To calculate what the short
antenna vill produce, you must include the impedance ratios.


First I've heard about verticals discussed with crystal radios.
Can't add anything.
Here's what Ben Tongue had to say about long wire characteristics.
https://web.archive.org/web/20131030052147/http://www.bentongue.com/xtalset/20MeaAGs/20MeaAGs.html

This is some kind of noise bridge. Usually a sensitive receiver in AM
mode is used as null indicator. Broadband noise is sent to the antenna
and R and C in the other leg. The R and C are adjusted until the
bridge is in balance and the resistance and capacitive reactance Xc is
read from the R and C settings. It is very handy e.g. when trimming a
wire antenna for resonance at a specific frequency. Start with a
slightly too long wire and measure resonance below allocated
frequency, reduce length until you are at desired frequency. No need
to transmit on frequencies allocated to other services during
trimming of the antenna.

The antenna system measured in this link seems quite strange and the
measured capacitance and resistance behaves also strangely.

For a short vertical, one would expect that the capacitance remains
nearly constant regardless of frequency and hence the capacitive
reactance is inversely proportional to frequency. The radiation
resistance should increase with the square of frequency (until 1/4
wavelength) but a lossy grounding resistance in series will swamp some
of this change.

When designing a transmitter system, one tries to get the expensive
RF power from the transmitter and radiated into the space around the
antenna. To get maximum power transfer, the source and load impedance
should be the same. If they aren't you have to include some low loss
matching tools between the transmitter and antenna (e.g. T or
Pi-match).

For a passive receiver, it is as desirable to transfer maximum
available power as in transmitting applications.

The maximum available power can be estimated if the field strength
[V/m] is known for a specific frequency. The maximum antenna capture
power is proportional to the capture area which inversely proportional
to the square of frequency and hence relative to the square of
wavelength.

Assuming field strength E of 2 mV/m so S = E˛/Z0 = 0.02˛/377= 1 uW/m˛
= -30 dBm/m˛.

For a full size dipole, the capture area A is 0.12 x lamda˛

f WL A P
[MHz] [m] [m˛] [dBm]
0.5 600 43000 +16
1.0 300 10800 +10
1.5 200 4800 +7

For a small size dipole, the figures are a few dB less.

If the field strength is only one tenth (0.2 ,V/m) subtract 20 dB from
those power levels calculated.

That is the theoretical maximum power available from a single antenna.
Depending on various losses, only a fraction will reach the
headphones.

With active amplifiers you can use ineffective antennas and badly
mismatched antennas on LF, MF and lower HF due to the large band
noise, so a significant signal loss is acceptable. On VHF, UHF and up
you really have to power match to get all available power into the
preamplifier.


By the way, is it cheating using a separate resonance circuit tuned
to a local strong station, rectifying the signal and using the DC to
power an emiter/source follower between the DX receiver resonant
circuit and detector ? After all, it is still a passive receive.

 

[amdx]

On 7/30/2019 1:42 AM, upsidedown@downunder.com wrote:

On Mon, 29 Jul 2019 14:39:49 -0500, amdx <nojunk@knology.net> wrote:


A decent antenna is very important with passive receivers. A short
vertical has nearly the same capture area as a full sized 1/4 wave
vertical antenna. The nasty thing with electrically short antennas is
that they have strong capacitive reactance and a radiation resistance
of perhaps only a few ohms (insteead of nominal 37 ohms of a 1/4 sized
antenna). The problem is getting all the captured power into yor LC
circuit.

There are several tricks to do this. Adding a top hat dcapacitanse to
your short vertical will help a lot. A T-antenna or Z-top hat
capacitance are often used. A series loading coil can be used to tune
out the antenna capacitive reactance. Now you have a resistive
impedance of a few ohms. Feed the antenna to a tap very close to
ground of your LC coil or use a few turn primary to perform the
impedance matching.
.

The other way of looking at short verticals is to talk about effective
heights, which is close to 1/4 wavelength even for a short antenna.
If the field strength [V/m] is known, then you can calculate the
signal voltage into a full sized vertical. To calculate what the short
antenna vill produce, you must include the impedance ratios.


First I've heard about verticals discussed with crystal radios.
Can't add anything.
Here's what Ben Tongue had to say about long wire characteristics.
https://web.archive.org/web/20131030052147/http://www.bentongue.com/xtalset/20MeaAGs/20MeaAGs.html

This is some kind of noise bridge. Usually a sensitive receiver in AM
mode is used as null indicator. Broadband noise is sent to the antenna
and R and C in the other leg. The R and C are adjusted until the
bridge is in balance and the resistance and capacitive reactance Xc is
read from the R and C settings. It is very handy e.g. when trimming a
wire antenna for resonance at a specific frequency. Start with a
slightly too long wire and measure resonance below allocated
frequency, reduce length until you are at desired frequency. No need
to transmit on frequencies allocated to other services during
trimming of the antenna.

The antenna system measured in this link seems quite strange and the
measured capacitance and resistance behaves also strangely.

First it's not a vertical, it''s a long wire and from what I gather
noy all that long.

For a short vertical, one would expect that the capacitance remains
nearly constant regardless of frequency and hence the capacitive
reactance is inversely proportional to frequency. The radiation
resistance should increase with the square of frequency (until 1/4
wavelength) but a lossy grounding resistance in series will swamp some
of this change.

When designing a transmitter system, one tries to get the expensive
RF power from the transmitter and radiated into the space around the
antenna. To get maximum power transfer, the source and load impedance
should be the same. If they aren't you have to include some low loss
matching tools between the transmitter and antenna (e.g. T or
Pi-match).

For a passive receiver, it is as desirable to transfer maximum
available power as in transmitting applications.

The maximum available power can be estimated if the field strength
[V/m] is known for a specific frequency. The maximum antenna capture
power is proportional to the capture area which inversely proportional
to the square of frequency and hence relative to the square of
wavelength.

Assuming field strength E of 2 mV/m so S = E²/Z0 = 0.02²/377= 1 uW/m²
= -30 dBm/m².

For a full size dipole, the capture area A is 0.12 x lamda²

f WL A P
[MHz] [m] [m²] [dBm]
0.5 600 43000 +16
1.0 300 10800 +10
1.5 200 4800 +7

For a small size dipole, the figures are a few dB less.

If the field strength is only one tenth (0.2 ,V/m) subtract 20 dB from
those power levels calculated.

That is the theoretical maximum power available from a single antenna.
Depending on various losses, only a fraction will reach the
headphones.

With active amplifiers you can use ineffective antennas and badly
mismatched antennas on LF, MF and lower HF due to the large band
noise, so a significant signal loss is acceptable. On VHF, UHF and up
you really have to power match to get all available power into the
preamplifier.


By the way, is it cheating using a separate resonance circuit tuned
to a local strong station, rectifying the signal and using the DC to
power an emiter/source follower between the DX receiver resonant
circuit and detector ? After all, it is still a passive receive.

I don't think it's cheating. There are circuits online showing how
people have done that. The next stop is putting big cap on the circuit
and charging it all day, before using the energy for night time
listening. That seem like a grey area, a very dark grey area.

Mikek

 

On Tue, 30 Jul 2019 10:17:49 -0500, amdx <nojunk@knology.net> wrote:

On 7/30/2019 1:42 AM, upsidedown@downunder.com wrote:
On Mon, 29 Jul 2019 14:39:49 -0500, amdx <nojunk@knology.net> wrote:


A decent antenna is very important with passive receivers. A short
vertical has nearly the same capture area as a full sized 1/4 wave
vertical antenna. The nasty thing with electrically short antennas is
that they have strong capacitive reactance and a radiation resistance
of perhaps only a few ohms (insteead of nominal 37 ohms of a 1/4 sized
antenna). The problem is getting all the captured power into yor LC
circuit.

There are several tricks to do this. Adding a top hat dcapacitanse to
your short vertical will help a lot. A T-antenna or Z-top hat
capacitance are often used. A series loading coil can be used to tune
out the antenna capacitive reactance. Now you have a resistive
impedance of a few ohms. Feed the antenna to a tap very close to
ground of your LC coil or use a few turn primary to perform the
impedance matching.
.

The other way of looking at short verticals is to talk about effective
heights, which is close to 1/4 wavelength even for a short antenna.
If the field strength [V/m] is known, then you can calculate the
signal voltage into a full sized vertical. To calculate what the short
antenna vill produce, you must include the impedance ratios.


First I've heard about verticals discussed with crystal radios.
Can't add anything.
Here's what Ben Tongue had to say about long wire characteristics.
https://web.archive.org/web/20131030052147/http://www.bentongue.com/xtalset/20MeaAGs/20MeaAGs.html

This is some kind of noise bridge. Usually a sensitive receiver in AM
mode is used as null indicator. Broadband noise is sent to the antenna
and R and C in the other leg. The R and C are adjusted until the
bridge is in balance and the resistance and capacitive reactance Xc is
read from the R and C settings. It is very handy e.g. when trimming a
wire antenna for resonance at a specific frequency. Start with a
slightly too long wire and measure resonance below allocated
frequency, reduce length until you are at desired frequency. No need
to transmit on frequencies allocated to other services during
trimming of the antenna.

The antenna system measured in this link seems quite strange and the
measured capacitance and resistance behaves also strangely.

First it's not a vertical, it''s a long wire and from what I gather
noy all that long.

From the discussion in this thread, I assumed that the idea was doing
weak signal DXing.

A horizontal line installed at a low hight will have a radiation
pattern pointing upwards due to the ground reflection. For this reason
it is effective only for NVIES communication.up to few hundred
kilometers. For longer distances, either the horizontal antenna must
be much higher (in the order of a wavelength) or vertical polarization
could be used.

Many think that in an inverted L- or T-antenna that the horizontal
wire is the actual antenna, while the vertical part is just a
feedline. In reality, the vertical "feedline" is responsible for the
long distance vertical polarization, while the horizontal part just
form a top hat capacitance (capacitive loading) making the vertical
antenna less (capacitively) reactive.

 

[amdx]

On 7/30/2019 11:30 AM, upsidedown@downunder.com wrote:

On Tue, 30 Jul 2019 10:17:49 -0500, amdx <nojunk@knology.net> wrote:

On 7/30/2019 1:42 AM, upsidedown@downunder.com wrote:
On Mon, 29 Jul 2019 14:39:49 -0500, amdx <nojunk@knology.net> wrote:


A decent antenna is very important with passive receivers. A short
vertical has nearly the same capture area as a full sized 1/4 wave
vertical antenna. The nasty thing with electrically short antennas is
that they have strong capacitive reactance and a radiation resistance
of perhaps only a few ohms (insteead of nominal 37 ohms of a 1/4 sized
antenna). The problem is getting all the captured power into yor LC
circuit.

There are several tricks to do this. Adding a top hat dcapacitanse to
your short vertical will help a lot. A T-antenna or Z-top hat
capacitance are often used. A series loading coil can be used to tune
out the antenna capacitive reactance. Now you have a resistive
impedance of a few ohms. Feed the antenna to a tap very close to
ground of your LC coil or use a few turn primary to perform the
impedance matching.
.

The other way of looking at short verticals is to talk about effective
heights, which is close to 1/4 wavelength even for a short antenna.
If the field strength [V/m] is known, then you can calculate the
signal voltage into a full sized vertical. To calculate what the short
antenna vill produce, you must include the impedance ratios.


First I've heard about verticals discussed with crystal radios.
Can't add anything.
Here's what Ben Tongue had to say about long wire characteristics.
https://web.archive.org/web/20131030052147/http://www.bentongue.com/xtalset/20MeaAGs/20MeaAGs.html

This is some kind of noise bridge. Usually a sensitive receiver in AM
mode is used as null indicator. Broadband noise is sent to the antenna
and R and C in the other leg. The R and C are adjusted until the
bridge is in balance and the resistance and capacitive reactance Xc is
read from the R and C settings. It is very handy e.g. when trimming a
wire antenna for resonance at a specific frequency. Start with a
slightly too long wire and measure resonance below allocated
frequency, reduce length until you are at desired frequency. No need
to transmit on frequencies allocated to other services during
trimming of the antenna.

The antenna system measured in this link seems quite strange and the
measured capacitance and resistance behaves also strangely.

First it's not a vertical, it''s a long wire and from what I gather
not all that long.

From the discussion in this thread, I assumed that the idea was doing
weak signal DXing.

A horizontal line installed at a low hight will have a radiation
pattern pointing upwards due to the ground reflection. For this reason
it is effective only for NVIES communication.up to few hundred
kilometers. For longer distances, either the horizontal antenna must
be much higher (in the order of a wavelength) or vertical polarization
could be used.

Many think that in an inverted L- or T-antenna that the horizontal
wire is the actual antenna, while the vertical part is just a
feedline. In reality, the vertical "feedline" is responsible for the
long distance vertical polarization, while the horizontal part just
form a top hat capacitance (capacitive loading) making the vertical
antenna less (capacitively) reactive.

I can make a few points and ask questions.
Historically a long wire was used for crystal radios. And yes your
right that a long wire is an inverted L antenna and the "feedline" is
much of the antenna if not all and the long wire part is a top hat.
To the best of my understanding at this point a short vertical is
going to have a much high capacitive reactance than a long wire (short
vertical with a long wire capacitive hat) Making it harder to match.
When I think of verticals I think of something tuned to resonance and
having close to 50 ohms (37 +) and no reactance. I read Jerry Sevicks
book on short verticals. OK, I read parts of it.
I never wanted to think this much!
The T antenna often was built with multiple parallel wires to increase
capacitance to ground to help with tuning.
Reading more on Ben's page it seems a somewhat short and low, long
wire antenna including ground resistance, and this is really only one
antenna, looks like 300pf and 11 ohms at 1MHz. 53ft long 14ft high.
I don't know how a vertical would compare and I assume the problem
would be tuning losses.
I lost my long wire when all the skyhooks were blown over by hurricane
Michael. Also lost my BOG when the neighbor cleared his lot of everything.
I'll get to play again after I finish building a new screened porch,
also need a new roof on my shed, it's now 23 years old, metal roof.
I realize I need to read for comprehension rather than just thinking
I know what I want to tell you. You were right about the long wire being
a vertical, but it really should have a top hat.
Mikek

 

On Tuesday, 30 July 2019 22:26:22 UTC+1, amdx wrote:

Historically a long wire was used for crystal radios. And yes your
right that a long wire is an inverted L antenna and the "feedline" is
much of the antenna if not all and the long wire part is a top hat.

That's not hard to disprove. I had a long wire antenna with horizontal feed wire. It worked very well, thus the horizontal section does act as an antenna, not just top capacitance.


NT

 

[amdx]

On 7/30/2019 7:36 PM, tabbypurr@gmail.com wrote:

On Tuesday, 30 July 2019 22:26:22 UTC+1, amdx wrote:

Historically a long wire was used for crystal radios. And yes your
right that a long wire is an inverted L antenna and the "feedline" is
much of the antenna if not all and the long wire part is a top hat.

That's not hard to disprove.

Please do, I have read several times the feed is part of the antenna.
Just how much?


I had a long wire antenna with horizontal feed wire. It worked very
well, thus the horizontal section does act as an antenna, not just top
capacitance.

NT

I had one too, and it worked well, but how well compared to just a
vertical. I don't know.

How does the pattern change over a vertical?
Let's discuss a real antenna. Radio 4ft from the ground, antenna goes
from 4ft up vertical 20ft then slopes up over 130ft to a height of 50ft.
Ground resistance, I don't know, pick something realistic but has been
nurtured to help lower it. Sandy loam soil.

Mikek

OH, I did a video when I had a 130ft long wire aiming West a
250ft BOG aiming North and a Mini Whip that is supposedly omni.
I'm in the Florida panhandle and the station 1530 is in Cincinnati Ohio.
I loved the BOG, that will be my first rebuild after all three were
destroyed by Hurricane Michael, when I finally get to it.
> https://www.youtube.com/watch?v=q8rBb2v13tg

In this video I did more of a band scan comparing the antennas.
I find it interesting to review after a year, you might too!

> https://www.youtube.com/watch?v=QuMwGDK6IhQ

 

On Tue, 30 Jul 2019 17:36:01 -0700 (PDT), tabbypurr@gmail.com wrote:

On Tuesday, 30 July 2019 22:26:22 UTC+1, amdx wrote:

Historically a long wire was used for crystal radios. And yes your
right that a long wire is an inverted L antenna and the "feedline" is
much of the antenna if not all and the long wire part is a top hat.

That's not hard to disprove. I had a long wire antenna with horizontal feed wire. It worked very well, thus the horizontal section does act as an antenna, not just top capacitance.

If we forget real long wire antennas such as Beverages that are
wavelengths long and assume that we are talking about horizontal wires
with one end hung high up in a tree and the receiver terminal inside
the house, the antenna is actually a sloper with a height difference
between wire end points. This absorbs the vertically polarized part of
the field. The wire doesn¨t have to perpendicular to earth to capture
any vertical component.

As far as I understand all LW/MW broadcast stations intended for local
ground wave reception has always been vertically polarized. Typically
a single mast with an elaborate grounding, such as 98 buried radials.

Especially on LW broadcast stations often two towers were used with
one or multiple horizontal wires installed between them forming a top
loading capacitance. A vertical radiator was then connected from the
transmitter to the center of the horizontal wire(s) forming a
T-antenna. Thanks to the top loading not so much loading coils and
less grounding networks were required.

In Poland they even build a 600 b high center feed half wave LW
dipole, which of course did not need a grounding network.
Unfortunately it crashed during maintenance several years ago.

 

On Wednesday, 31 July 2019 02:07:19 UTC+1, amdx wrote:

On 7/30/2019 7:36 PM, tabbypurr wrote:
On Tuesday, 30 July 2019 22:26:22 UTC+1, amdx wrote:

Historically a long wire was used for crystal radios. And yes your
right that a long wire is an inverted L antenna and the "feedline" is
much of the antenna if not all and the long wire part is a top hat.

That's not hard to disprove.

Please do, I have read several times the feed is part of the antenna.
Just how much?

I had a long wire antenna with horizontal feed wire. It worked very
well, thus the horizontal section does act as an antenna, not just top
capacitance.

I had one too, and it worked well, but how well compared to just a
vertical. I don't know.

How does the pattern change over a vertical?
Let's discuss a real antenna. Radio 4ft from the ground, antenna goes
from 4ft up vertical 20ft then slopes up over 130ft to a height of 50ft.
Ground resistance, I don't know, pick something realistic but has been
nurtured to help lower it. Sandy loam soil.

Mikek

OH, I did a video when I had a 130ft long wire aiming West a
250ft BOG aiming North and a Mini Whip that is supposedly omni.
I'm in the Florida panhandle and the station 1530 is in Cincinnati Ohio.
I loved the BOG, that will be my first rebuild after all three were
destroyed by Hurricane Michael, when I finally get to it.
https://www.youtube.com/watch?v=q8rBb2v13tg

In this video I did more of a band scan comparing the antennas.
I find it interesting to review after a year, you might too!

https://www.youtube.com/watch?v=QuMwGDK6IhQ

interesting comparison.
To compare the upright versus horizontal sections of a non-beverage a start would be to receive using each section alone as well as combined: I don't have the setup to do that now.


NT

 

[amdx]

On 7/25/2019 2:40 PM, upsidedown@downunder.com wrote:

On Thu, 25 Jul 2019 13:10:47 -0500, amdx <nojunk@knology.net> wrote:


In one of my posts, I mentioned that someone is putting together a
ring down Q meter and trying to save a few bucks going with high Q smd
vs a good variable air cap. This is crystal radio stuff and Qs can get
as high as 1500. So, in order to improve accuracy I expect the best cap
at a reasonable price. But I would hope it is 10x higher Q than the highest
Q coil to be measured. Even with that, it would still measure the coil Q
down my 10%. (I didn't run the numbers, but it's close)

So this is for a crystal set for receiving AM broadcasts in the 0.5 -
1,5 MHz band ? For AM reception, the detector needs the carrier and at
least of one sideband. Assuming 5 kHz required bandwidth, that will
required loaded Ql at the low end of the band of 100 and 300 at the
top of the band.

On the other hand, the unloaded Qu should be a few times larger than
the loaded Ql in order to minimize passband insertion losses. The
insertion loss is given by

Loss_dB = 20 log (1/ (1-Ql/Qu) )

Assuming (unrealistically) that Qu remains at 1500 all over the band.
Thus at the low end of the band the insertion loss is 0.6 dB and at
1.5 MHz 1.9 dB. A 10 % error in the Qu measurement doesn't affect the
insertion loss very much.

My best coil has Q=1250 at 500kHz, it peaks at Q=1500 at 800kHz, and
drops to Q=850 at 1700kHz.
Everyone seems very concerned about Q being to high. A builder of a
high end crystal radio would be proud to have that problem, it is so
easily fixed, where building to a spec of having that problem is difficult.

Mikek