On Mon, 27 Apr 2009 05:32:07 -0700 (PDT), David
wrote:

On Apr 25, 10:51*pm, Tim Wescott wrote:
David wrote:
Was just wandering if anyone has used or experimented with television
IF, Video and Detector coils, most are slug tuned coils that have a
few uh to several hundred uh, some are sheilded some are not, i have
about 500 that i bought years ago, a lot of them look very close too
the old loopstick type coils, looking for
ideas.
Thanks David

They'll have very low Q, and therefore not really be suitable for a
crystal radio, where low-Q coils fight your ability to get good
selectivity without burning up all your signal before it gets to the
headphones.

There's a whole bunch of _other_ cool things you can do with them, just
not Xtal sets.

--

Tim Wescott
Wescott Design Serviceshttp://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details athttp://www.wescottdesign.com/actfes/actfes.html

What would be a good Q range for AM broadcast & Shortwave bands.

If your _loaded_ Q is 100, the -3 dB bandwidth at 1 MHz would be 10
kHz (i.e. +/- 5 kHz from the carrier). The question is, what should
the _un_loaded Q be ?

If you have a full sized antenna, the signal strength would be
sufficient even with an unloaded Q of just 100-200.

At the middle of the HF band (10 MHz) a loaded Q of 1000 would be
required for a single station bandwidth and quite large helical
resonators would be required to get a usable unloaded Q without
damping the resonant circuit Q too much.

Paul OH3LWR

Paul Keinanen wrote:
On Mon, 27 Apr 2009 05:32:07 -0700 (PDT), David
wrote:

On Apr 25, 10:51 pm, Tim Wescott wrote:
David wrote:
Was just wandering if anyone has used or experimented with television
IF, Video and Detector coils, most are slug tuned coils that have a
few uh to several hundred uh, some are sheilded some are not, i have
about 500 that i bought years ago, a lot of them look very close too
the old loopstick type coils, looking for
ideas.
Thanks David
They'll have very low Q, and therefore not really be suitable for a
crystal radio, where low-Q coils fight your ability to get good
selectivity without burning up all your signal before it gets to the
headphones.

There's a whole bunch of _other_ cool things you can do with them, just
not Xtal sets.

--

Tim Wescott
Wescott Design Serviceshttp://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details athttp://www.wescottdesign.com/actfes/actfes.html
What would be a good Q range for AM broadcast & Shortwave bands.

If your _loaded_ Q is 100, the -3 dB bandwidth at 1 MHz would be 10
kHz (i.e. +/- 5 kHz from the carrier). The question is, what should
the _un_loaded Q be ?

If you have a full sized antenna, the signal strength would be
sufficient even with an unloaded Q of just 100-200.

At the middle of the HF band (10 MHz) a loaded Q of 1000 would be
required for a single station bandwidth and quite large helical
resonators would be required to get a usable unloaded Q without
damping the resonant circuit Q too much.

Paul OH3LWR

What Paul didn't mention is that the ratio between the unloaded and
loaded Q is pretty much the ratio between the energy coming from the
antenna and the energy that's wasted in the tank.

I.e. if your unloaded Q equals your loaded Q, then you're using up _all_
the energy in the tank, and there's none left over for your headphones.
If your unloaded Q is 200 and your loaded is the 100 that you'd want
for AM reception, you're using as much energy heating up your tank
circuit as you are using to drive your headphones.

So insanely efficient tank circuits are a necessity for a crystal set.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

On Mon, 27 Apr 2009 13:43:41 -0700, Tim Wescott
wrote:

Paul Keinanen wrote:
On Mon, 27 Apr 2009 05:32:07 -0700 (PDT), David
wrote:

On Apr 25, 10:51 pm, Tim Wescott wrote:
David wrote:
Was just wandering if anyone has used or experimented with television
IF, Video and Detector coils, most are slug tuned coils that have a
few uh to several hundred uh, some are sheilded some are not, i have
about 500 that i bought years ago, a lot of them look very close too
the old loopstick type coils, looking for
ideas.
Thanks David
They'll have very low Q, and therefore not really be suitable for a
crystal radio, where low-Q coils fight your ability to get good
selectivity without burning up all your signal before it gets to the
headphones.

There's a whole bunch of _other_ cool things you can do with them, just
not Xtal sets.

--

Tim Wescott
Wescott Design Serviceshttp://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details athttp://www.wescottdesign.com/actfes/actfes.html
What would be a good Q range for AM broadcast & Shortwave bands.

If your _loaded_ Q is 100, the -3 dB bandwidth at 1 MHz would be 10
kHz (i.e. +/- 5 kHz from the carrier). The question is, what should
the _un_loaded Q be ?

If you have a full sized antenna, the signal strength would be
sufficient even with an unloaded Q of just 100-200.

At the middle of the HF band (10 MHz) a loaded Q of 1000 would be
required for a single station bandwidth and quite large helical
resonators would be required to get a usable unloaded Q without
damping the resonant circuit Q too much.

Paul OH3LWR

What Paul didn't mention is that the ratio between the unloaded and
loaded Q is pretty much the ratio between the energy coming from the
antenna and the energy that's wasted in the tank.

I.e. if your unloaded Q equals your loaded Q, then you're using up _all_
the energy in the tank, and there's none left over for your headphones.
If your unloaded Q is 200 and your loaded is the 100 that you'd want
for AM reception, you're using as much energy heating up your tank
circuit as you are using to drive your headphones.

I fully agree with this. With a Qu/Ql ratio 2:1 you end up with only 6
dB insertion loss.

However, the antenna capture area and hence the captured power (for a
constant field strength and hence constant power density) is inversely
proportional to the square of frequency (-6 dB/octave).

While a 1/2 wavelength dipole might be sufficient to feed a crystal
detector at 1 MHz, a 1/2 wave dipole at 10 MHz will unfortunately
produce only 1/100 the power.

Paul OH3LWR

On Apr 27, 10:30*am, Paul Keinanen wrote:
On Mon, 27 Apr 2009 05:32:07 -0700 (PDT), David
wrote:



On Apr 25, 10:51*pm, Tim Wescott wrote:
David wrote:
Was just wandering if anyone has used or experimented with television
IF, Video and Detector coils, most are slug tuned coils that have a
few uh to several hundred uh, some are sheilded some are not, i have
about 500 that i bought years ago, a lot of them look very close too
the old loopstick type coils, looking for
ideas.
Thanks David

They'll have very low Q, and therefore not really be suitable for a
crystal radio, where low-Q coils fight your ability to get good
selectivity without burning up all your signal before it gets to the
headphones.

There's a whole bunch of _other_ cool things you can do with them, just
not Xtal sets.

--

Tim Wescott
Wescott Design Serviceshttp://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details athttp://www.wescottdesign.com/actfes/actfes.html

What would be a good Q range for AM broadcast & Shortwave bands.

If your _loaded_ Q is 100, the -3 dB bandwidth at 1 MHz would be 10
kHz (i.e. +/- 5 kHz from the carrier). The question is, what should
the _un_loaded Q be ?

If you have a full sized antenna, the signal strength would be
sufficient even with an unloaded Q of just 100-200.

At the middle of the HF band (10 MHz) a loaded Q of 1000 would be
required for a single station bandwidth and quite large helical
resonators would be required to get a usable unloaded Q without
damping the resonant circuit Q too much.

Paul OH3LWR

To put some numbers on what Paul suggested:

If I want an unloaded coil Q of 2000 at 10MHz, I'd expect to need a
coil about 5 inches (13cm) diameter and 10 inches (26cm) long--or
similar. That assumes no loss to radiation. If I shield it to make a
helical resonator, the Q will actually be lowered slightly, though
such a large coil may have enough loss to radiation that it would be a
wash between turning it into a helical resonator or leaving it in free
air. Of course, with the shielding, it's less susceptible to changes
in the environment around it. Anyway, the shield for a helical
resonator should be a couple times the diameter of the coil, so it's a
rather large arrangement anyway!

If you have very sensitive earphones (and sensitive ears!) and a good
antenna, what may matter more than keeping the loss down to an
absolute minimum is getting rid of interfering signals. A single-
tuned circuit with 10kHz -3dB bandwidth offers only 20dB attenuation
of a signal 50kHz away, and a signal 200kHz away is attenuated only
about 32dB (assuming I didn't mess up my mental arithmetic). That's
not a lot if you live in a metropolitan area with several stations
nearby, and you want to hear the ones from far away. You can make the
tuner with two or even three tuned circuits that are properly coupled,
and get much better attenuation of those unwanted signals. But more
tuned circuits means more loss in the tuner, too, even if you use high
Q coils.

It's a really good idea to check out what others have done to advance
the art of winding high Q coils for AM broadcast band frequencies, and
of the circuits to use those coils to best advantage.

Cheers,
Tom

K7ITM wrote:


To put some numbers on what Paul suggested:

If I want an unloaded coil Q of 2000 at 10MHz,

I stopped here.


I'd expect to need a....

No way you'll ever see 2000 Q at 10 Mcs. Can't happen. Some guys are
approaching 2000 at 1 MC BCB but there's lots of expensive hoops to jump
through to reach that point. Simply cannot be had at 10 Mcs. 200-300
on a good SW coil is about all that can be achieved.



If you have very sensitive earphones (and sensitive ears!) and a good
antenna, what may matter more than keeping the loss down to an
absolute minimum is getting rid of interfering signals.

Thats Q.

=
It's a really good idea to check out what others have done to advance
the art of winding high Q coils for AM broadcast band frequencies, and
of the circuits to use those coils to best advantage.

Indeed. But that agreed to there's no method to make the same numbers
and techniques work at 10 Mcs. You really cannot achieve the numbers on
SW as you can BCB given the 10x frequency difference.

On Mon, 27 Apr 2009 16:34:23 -0700 (PDT), K7ITM wrote:

If you have very sensitive earphones (and sensitive ears!) and a good
antenna, what may matter more than keeping the loss down to an
absolute minimum is getting rid of interfering signals. A single-
tuned circuit with 10kHz -3dB bandwidth offers only 20dB attenuation
of a signal 50kHz away, and a signal 200kHz away is attenuated only
about 32dB (assuming I didn't mess up my mental arithmetic). That's
not a lot if you live in a metropolitan area with several stations
nearby, and you want to hear the ones from far away. You can make the
tuner with two or even three tuned circuits that are properly coupled,
and get much better attenuation of those unwanted signals. But more
tuned circuits means more loss in the tuner, too, even if you use high
Q coils.

Unless you live very near an international SW broadcasters, how do you
expect to get any usable amplitude modulated signal in the middle of
the SW band for your crystal set ?

To make the situation even worse, the power delivered by a matched
dipole at 10 MHz is only 1/100 (-20 dB) of the power delivered by a
matched dipole on 1 MHz due to the antenna capture area.

Paul OH3LWR

On Apr 27, 10:59*pm, Paul Keinanen wrote:
On Mon, 27 Apr 2009 16:34:23 -0700 (PDT), K7ITM wrote:
If you have very sensitive earphones (and sensitive ears!) and a good
antenna, what may matter more than keeping the loss down to an
absolute minimum is getting rid of interfering signals. *A single-
tuned circuit with 10kHz -3dB bandwidth offers only 20dB attenuation
of a signal 50kHz away, and a signal 200kHz away is attenuated only
about 32dB (assuming I didn't mess up my mental arithmetic). *That's
not a lot if you live in a metropolitan area with several stations
nearby, and you want to hear the ones from far away. *You can make the
tuner with two or even three tuned circuits that are properly coupled,
and get much better attenuation of those unwanted signals. *But more
tuned circuits means more loss in the tuner, too, even if you use high
Q coils.

Unless you live very near an international SW broadcasters, how do you
expect to get any usable amplitude modulated signal in the middle of
the SW band for your crystal set ?

To make the situation even worse, the power delivered by a matched
dipole at 10 MHz is only 1/100 (-20 dB) of the power delivered by a
matched dipole on 1 MHz due to the antenna capture area.

Paul OH3LWR

Actually, I was thinking in the paragraph you quoted more of MW
broadcast, but since you mention SW: I have it on good authority that
European SW broadcasters put 7MHz signals into the East coast of the
US at levels up to close to 0dBm into a receiver's antenna terminals
when the skip is right. That's using an antenna with a bit of gain
over a dipole, but nothing fantastic. (That level gave me a goal for
strong-signal handling for an HF receiver I recently put into
production.)

Cheers,
Tom

On Apr 27, 8:02*pm, Bill M wrote:
K7ITM wrote:

To put some numbers on what Paul suggested:

If I want an unloaded coil Q of 2000 at 10MHz,

I stopped here.

I'd expect to need a....

No way you'll ever see 2000 Q at 10 Mcs. Can't happen. Some guys are
approaching 2000 at 1 MC BCB but there's lots of expensive hoops to jump
through to reach that point. *Simply cannot be had at 10 Mcs. *200-300
on a good SW coil is about all that can be achieved.
....
Interesting comment. In the filters I build for test fixtures, I use
air-core coils that are about 1" diameter and 1" long, and they give
me Qu in excess of 300 at 10MHz. For what I do, I don't need Qu up in
the thousands, and don't have room for really big coils, but can you
give me a reason I shouldn't expect Qu to scale linearly with size up
to the point where radiation losses become significant?

Can you tell me why I should think that the inductance calculator at
http://hamwaves.com/antennas/inductance.html is not giving me accurate
results when I put in, say, D=130mm, n=20, l=260mm, d=7mm, and
f=10MHz? It agrees with other independent ways I have to estimate the
Qu of the ~1 inch coils I build, and those coils measure within
engineering tolerance of the estimates.

When you go to very large coils like this, you have to be careful
about the self-resonance becoming too low, but in the example above,
it's (barely) OK at 10MHz. (Actually, you better be careful about the
self-resonance of any coil...) Fewer turns of larger diameter
"wire" (tubing: cheaper, and easier to work with) can yield about the
same Qu and a considerably higher self-resonance.

Cheers,
Tom

K7ITM wrote:
On Apr 27, 8:02 pm, Bill M wrote:
K7ITM wrote:

To put some numbers on what Paul suggested:
If I want an unloaded coil Q of 2000 at 10MHz,
I stopped here.

I'd expect to need a....

No way you'll ever see 2000 Q at 10 Mcs. Can't happen. Some guys are
approaching 2000 at 1 MC BCB but there's lots of expensive hoops to jump
through to reach that point. Simply cannot be had at 10 Mcs. 200-300
on a good SW coil is about all that can be achieved.
...
Interesting comment. In the filters I build for test fixtures, I use
air-core coils that are about 1" diameter and 1" long, and they give
me Qu in excess of 300 at 10MHz. For what I do, I don't need Qu up in
the thousands, and don't have room for really big coils, but can you
give me a reason I shouldn't expect Qu to scale linearly with size up
to the point where radiation losses become significant?

Can you tell me why I should think that the inductance calculator at
http://hamwaves.com/antennas/inductance.html is not giving me accurate
results when I put in, say, D=130mm, n=20, l=260mm, d=7mm, and
f=10MHz? It agrees with other independent ways I have to estimate the
Qu of the ~1 inch coils I build, and those coils measure within
engineering tolerance of the estimates.

Self-capacitance (ultimately self-resonance) is always a contributing
factor that prevents coils from achieving their maximum theoretical Q.
Estimating coils whose Q is going to fall in the 200 range for other
reasons is relatively easy but that doesn't mean you can scale upwards
proportionately.

I build air coils in the 3 inch range along the lines of what is
pictured here, http://www.sparkbench.com/homebrew/grebe/cr18.html

They only *measure* in the 250 range. Silver-plated wire could
certainly improve a coil of this size but no way would you achieve
numbers like 2000.

-Bill

On Mon, 27 Apr 2009 16:34:23 -0700 (PDT), K7ITM wrote:

If I want an unloaded coil Q of 2000 at 10MHz, I'd expect to need a
coil about 5 inches (13cm) diameter and 10 inches (26cm) long--or
similar. That assumes no loss to radiation. If I shield it to make a
helical resonator, the Q will actually be lowered slightly, though
such a large coil may have enough loss to radiation that it would be a
wash between turning it into a helical resonator or leaving it in free
air. Of course, with the shielding, it's less susceptible to changes
in the environment around it. Anyway, the shield for a helical
resonator should be a couple times the diameter of the coil, so it's a
rather large arrangement anyway!

1/4 wave filters used in repeater duplexers have quite high unloaded-Q
and are available to at least down to 50 MHz. Of course these are
long, but in order to reduce total shape, these might be bent into
U-shape.

To go into even lower frequencies, the resonator can be bent into a
helix. At least the design nomogram in old ARRL handbooks seem to
indicate that with sufficient size very high unloaded-Q could be
achieved (up to several thousands). Of course the helix itself and the
inside of the resonator may have to be silver plated.

Paul OH3LWR