Driver to drive?

[rickman]

On 3/27/2017 7:16 PM, Clifford Heath wrote:

On 27/03/17 23:25, amdx wrote:
On 3/27/2017 6:57 AM, Tauno Voipio wrote:
Joerg, you seem not understand the innermost sense of the crystal-
radio people. They are closely related to audiophools, and it is
quite impossible to use sensible technical argumentation here.

I don't get that at all, can you back that up with any facts?

~1MHz, Q=500, bandwidth ~ 2KHz. Remind me why you need Q>1500?
More voltage does not create better audio.

Your numbers are meaningless because a coil is not a radio. Why don't
you learn about the actual topic rather than just trying to rain on
other's parade?

Anyone can throw rocks.

--

Rick C

 

[amdx]

On 3/27/2017 6:16 PM, Clifford Heath wrote:

On 27/03/17 23:25, amdx wrote:
On 3/27/2017 6:57 AM, Tauno Voipio wrote:
Joerg, you seem not understand the innermost sense of the crystal-
radio people. They are closely related to audiophools, and it is
quite impossible to use sensible technical argumentation here.

I don't get that at all, can you back that up with any facts?

~1MHz, Q=500, bandwidth ~ 2KHz. Remind me why you need Q>1500?

You haven't connected an antenna, and tried to drive a headset yet.


> More voltage does not create better audio.

But if it is a very weak signal on the antenna, you don't want to
waste any signal in loss resistances.

Mikek



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

 

[rickman]

On 3/27/2017 7:58 PM, Joerg wrote:

On 2017-03-27 16:16, Clifford Heath wrote:
On 27/03/17 23:25, amdx wrote:
On 3/27/2017 6:57 AM, Tauno Voipio wrote:
Joerg, you seem not understand the innermost sense of the crystal-
radio people. They are closely related to audiophools, and it is
quite impossible to use sensible technical argumentation here.

I don't get that at all, can you back that up with any facts?

~1MHz, Q=500, bandwidth ~ 2KHz. Remind me why you need Q>1500?
More voltage does not create better audio.


That's what I was wondering all the time. In the ranges tested there are
largely just AM stations, no CW or morse code. Even at 10kHz BW the
audio experience will not be very pleasing, it'll sound more like on a
telephone.

How much bandwidth is available on an AM radio station??? Do you
actually know much about crystal radios?

Then there is the tempco. Someone opens a window and whoops the resonant
frequency goes somewhere else.

Again, you are not speaking from knowledge. There are ham radio
antennas with exactly this sort of high Q and they manage to maintain
tuning during 100 watt transmissions.

Why are you guys trying to discuss a topic you actually know little about.

--

Rick C

 

[Clifford Heath]

On 28/03/17 14:47, rickman wrote:

On 3/27/2017 12:22 PM, Joerg wrote:
On 2017-03-27 07:59, rickman wrote:
On 3/27/2017 10:46 AM, Joerg wrote:

The Q is over 500. It was claimed in this thread that PVC is not
suitable as coil winding material and this proves that it is quite
suitable. Which I already knew because I've used it in RF power amps
decades ago.

Again, context. You are living in a different world. PVC is *not*
suitable in the crystal radio world because there are *much* better
materials. If PVC was the only material available it would be a *great*
coil support. If mud was the only material available it would be a
*great* coil support.


Can you explain why one even want a Q in excess of 500 in the AM band?

Q is a measure of the losses. Having a high Q in the coil means the
coil has lower losses. Having a higher Q in the tuning capacitor means
it has lower losses. The lower the losses the more power that ends up
in the headphones.

You have this quite wrong. A Q of 500 is a loss of 0.2%, and
1500 is a loss of only 0.067%. Increase your coil area by 0.13%
(a fraction of a millimeter of diameter) and you recover the
power you lost by "only" having a Q of 500, by gathering more
power to start with.

Furthermore, because the signal of interest spreads +-5Khz or so,
when you use a super high Q, you *reject* the parts of the signal
that are outside the passband. So yeah, you get more voltage for
for the low audio frequencies, but *less power overall*.

Duh. Doesn't sound like such a good deal now, does it?

Clifford Heath.

 

[Clifford Heath]

On 28/03/17 14:33, rickman wrote:

On 3/27/2017 7:58 PM, Joerg wrote:
On 2017-03-27 16:16, Clifford Heath wrote:
On 27/03/17 23:25, amdx wrote:
On 3/27/2017 6:57 AM, Tauno Voipio wrote:
Joerg, you seem not understand the innermost sense of the crystal-
radio people. They are closely related to audiophools, and it is
quite impossible to use sensible technical argumentation here.

I don't get that at all, can you back that up with any facts?

~1MHz, Q=500, bandwidth ~ 2KHz. Remind me why you need Q>1500?
More voltage does not create better audio.


That's what I was wondering all the time. In the ranges tested there are
largely just AM stations, no CW or morse code. Even at 10kHz BW the
audio experience will not be very pleasing, it'll sound more like on a
telephone.

How much bandwidth is available on an AM radio station??? Do you
actually know much about crystal radios?

The carrier, and the sidebands, which spread either side by the
bandwidth of the audio being broadcast - perhaps 5 or 8KHz.
That means as soon as your Q exceeds 200 (@1MHz), you start to
reject some of the transmitted power.

Then there is the tempco. Someone opens a window and whoops the resonant
frequency goes somewhere else.

Again, you are not speaking from knowledge. There are ham radio
antennas with exactly this sort of high Q and they manage to maintain
tuning during 100 watt transmissions.

Why are you guys trying to discuss a topic you actually know little about

You really know so little that you can't even conceive of how little you
know.

 

[Clifford Heath]

On 28/03/17 13:18, amdx wrote:

On 3/27/2017 6:16 PM, Clifford Heath wrote:
On 27/03/17 23:25, amdx wrote:
On 3/27/2017 6:57 AM, Tauno Voipio wrote:
Joerg, you seem not understand the innermost sense of the crystal-
radio people. They are closely related to audiophools, and it is
quite impossible to use sensible technical argumentation here.

I don't get that at all, can you back that up with any facts?

~1MHz, Q=500, bandwidth ~ 2KHz. Remind me why you need Q>1500?

You haven't connected an antenna, and tried to drive a headset yet.

Umm, I think that was me in about 1971.

More voltage does not create better audio.

But if it is a very weak signal on the antenna, you don't want to
waste any signal in loss resistances.

You start to *reject* some of the received power as soon as the
Q passes 200ish, and you destroy the audio at the same time.

You can quadruple your received power by doubling your coil
diameter, or fitting a longer wire. That's *far* FAR more
effective than saving 0.2% by using higher Q.

With a crystal ear-piece, you still may have an impedance matching
problem. For that, you should use an audio transformer *after*
the detector.

Sorry to puncture your dogma.

 

[piglet]

On 28/03/2017 02:03, Sylvia Else wrote:

On 28/03/2017 10:25 AM, Jim Thompson wrote:

http://www.analog-innovations.com/SED/CD-Ignition-Basic.pdf

http://www.analog-innovations.com/SED/CDI_Inductor.jpg> ...Jim
Thompson


Don't quite see how that works - does it rely on the reverse breakdown
of D3?

Sylvia.

D3 acts normally, the output is a large negative spike.

piglet

 

[rickman]

On 3/28/2017 3:15 AM, Clifford Heath wrote:

On 28/03/17 14:47, rickman wrote:
On 3/27/2017 12:22 PM, Joerg wrote:
On 2017-03-27 07:59, rickman wrote:
On 3/27/2017 10:46 AM, Joerg wrote:

The Q is over 500. It was claimed in this thread that PVC is not
suitable as coil winding material and this proves that it is quite
suitable. Which I already knew because I've used it in RF power amps
decades ago.

Again, context. You are living in a different world. PVC is *not*
suitable in the crystal radio world because there are *much* better
materials. If PVC was the only material available it would be a
*great*
coil support. If mud was the only material available it would be a
*great* coil support.


Can you explain why one even want a Q in excess of 500 in the AM band?

Q is a measure of the losses. Having a high Q in the coil means the
coil has lower losses. Having a higher Q in the tuning capacitor means
it has lower losses. The lower the losses the more power that ends up
in the headphones.

You have this quite wrong. A Q of 500 is a loss of 0.2%, and
1500 is a loss of only 0.067%. Increase your coil area by 0.13%
(a fraction of a millimeter of diameter) and you recover the
power you lost by "only" having a Q of 500, by gathering more
power to start with.

Furthermore, because the signal of interest spreads +-5Khz or so,
when you use a super high Q, you *reject* the parts of the signal
that are outside the passband. So yeah, you get more voltage for
for the low audio frequencies, but *less power overall*.

Duh. Doesn't sound like such a good deal now, does it?

You trimmed the part of my post that dealt with the bandwidth issue.
Why don't you read that again?

Just like Joerg you are applying knowledge of electronics to part of a
receiver without understanding how it all works together.

Oh, and these receivers typically use a long wire antenna, not the coil,
to collect the signal.

--

Rick C

 

[Jasen Betts]

On 2017-03-27, Joerg <news@analogconsultants.com> wrote:

On 2017-03-27 16:16, Clifford Heath wrote:
On 27/03/17 23:25, amdx wrote:
On 3/27/2017 6:57 AM, Tauno Voipio wrote:
Joerg, you seem not understand the innermost sense of the crystal-
radio people. They are closely related to audiophools, and it is
quite impossible to use sensible technical argumentation here.

I don't get that at all, can you back that up with any facts?

~1MHz, Q=500, bandwidth ~ 2KHz. Remind me why you need Q>1500?
More voltage does not create better audio.


That's what I was wondering all the time. In the ranges tested there are
largely just AM stations, no CW or morse code. Even at 10kHz BW the
audio experience will not be very pleasing, it'll sound more like on a
telephone.

in a crystal radio the tank is fairly heavily loaded that reduces the
effective Q, every picowatt that isn't lost in the tank parts is a
picowatt you can send to the earpiece.

--
This email has not been checked by half-arsed antivirus software

 

[rickman]

On 3/28/2017 3:18 AM, Clifford Heath wrote:

On 28/03/17 14:33, rickman wrote:
On 3/27/2017 7:58 PM, Joerg wrote:
On 2017-03-27 16:16, Clifford Heath wrote:
On 27/03/17 23:25, amdx wrote:
On 3/27/2017 6:57 AM, Tauno Voipio wrote:
Joerg, you seem not understand the innermost sense of the crystal-
radio people. They are closely related to audiophools, and it is
quite impossible to use sensible technical argumentation here.

I don't get that at all, can you back that up with any facts?

~1MHz, Q=500, bandwidth ~ 2KHz. Remind me why you need Q>1500?
More voltage does not create better audio.


That's what I was wondering all the time. In the ranges tested there are
largely just AM stations, no CW or morse code. Even at 10kHz BW the
audio experience will not be very pleasing, it'll sound more like on a
telephone.

How much bandwidth is available on an AM radio station??? Do you
actually know much about crystal radios?

The carrier, and the sidebands, which spread either side by the
bandwidth of the audio being broadcast - perhaps 5 or 8KHz.
That means as soon as your Q exceeds 200 (@1MHz), you start to
reject some of the transmitted power.

Determined by the Q of the resonant circuit in the radio, not the Q of
the coil.

Then there is the tempco. Someone opens a window and whoops the resonant
frequency goes somewhere else.

Again, you are not speaking from knowledge. There are ham radio
antennas with exactly this sort of high Q and they manage to maintain
tuning during 100 watt transmissions.

Why are you guys trying to discuss a topic you actually know little about

You really know so little that you can't even conceive of how little you
know.

I can clearly see what you don't understand. Why are you being rude
about it?

--

Rick C

 

[rickman]

On 3/28/2017 3:22 AM, Clifford Heath wrote:

On 28/03/17 13:18, amdx wrote:
On 3/27/2017 6:16 PM, Clifford Heath wrote:
On 27/03/17 23:25, amdx wrote:
On 3/27/2017 6:57 AM, Tauno Voipio wrote:
Joerg, you seem not understand the innermost sense of the crystal-
radio people. They are closely related to audiophools, and it is
quite impossible to use sensible technical argumentation here.

I don't get that at all, can you back that up with any facts?

~1MHz, Q=500, bandwidth ~ 2KHz. Remind me why you need Q>1500?

You haven't connected an antenna, and tried to drive a headset yet.

Umm, I think that was me in about 1971.

More voltage does not create better audio.

But if it is a very weak signal on the antenna, you don't want to
waste any signal in loss resistances.

You start to *reject* some of the received power as soon as the
Q passes 200ish, and you destroy the audio at the same time.

You can quadruple your received power by doubling your coil
diameter, or fitting a longer wire. That's *far* FAR more
effective than saving 0.2% by using higher Q.

With a crystal ear-piece, you still may have an impedance matching
problem. For that, you should use an audio transformer *after*
the detector.

Sorry to puncture your dogma.

You don't have any idea of what he wrote. Read it again and try to
understand what he is talking about before you dismiss it so (actually
not so) glibly.

--

Rick C

 

[Clifford Heath]

On 28/03/17 18:42, rickman wrote:

On 3/28/2017 3:15 AM, Clifford Heath wrote:
On 28/03/17 14:47, rickman wrote:
On 3/27/2017 12:22 PM, Joerg wrote:
On 2017-03-27 07:59, rickman wrote:
On 3/27/2017 10:46 AM, Joerg wrote:

The Q is over 500. It was claimed in this thread that PVC is not
suitable as coil winding material and this proves that it is quite
suitable. Which I already knew because I've used it in RF power amps
decades ago.

Again, context. You are living in a different world. PVC is *not*
suitable in the crystal radio world because there are *much* better
materials. If PVC was the only material available it would be a
*great*
coil support. If mud was the only material available it would be a
*great* coil support.


Can you explain why one even want a Q in excess of 500 in the AM band?

Q is a measure of the losses. Having a high Q in the coil means the
coil has lower losses. Having a higher Q in the tuning capacitor means
it has lower losses. The lower the losses the more power that ends up
in the headphones.

You have this quite wrong. A Q of 500 is a loss of 0.2%, and
1500 is a loss of only 0.067%. Increase your coil area by 0.13%
(a fraction of a millimeter of diameter) and you recover the
power you lost by "only" having a Q of 500, by gathering more
power to start with.

Furthermore, because the signal of interest spreads +-5Khz or so,
when you use a super high Q, you *reject* the parts of the signal
that are outside the passband. So yeah, you get more voltage for
for the low audio frequencies, but *less power overall*.

Duh. Doesn't sound like such a good deal now, does it?

You trimmed the part of my post that dealt with the bandwidth issue. Why
don't you read that again?

Because you said 10KHz, when your bandwidth is nothing like that.
I just couldn't be bothered to call you on all your
lie^H^H^Halternative facts

 

[rickman]

On 3/28/2017 4:07 AM, Clifford Heath wrote:

On 28/03/17 18:42, rickman wrote:
On 3/28/2017 3:15 AM, Clifford Heath wrote:
On 28/03/17 14:47, rickman wrote:
On 3/27/2017 12:22 PM, Joerg wrote:
On 2017-03-27 07:59, rickman wrote:
On 3/27/2017 10:46 AM, Joerg wrote:

The Q is over 500. It was claimed in this thread that PVC is not
suitable as coil winding material and this proves that it is quite
suitable. Which I already knew because I've used it in RF power amps
decades ago.

Again, context. You are living in a different world. PVC is *not*
suitable in the crystal radio world because there are *much* better
materials. If PVC was the only material available it would be a
*great*
coil support. If mud was the only material available it would be a
*great* coil support.


Can you explain why one even want a Q in excess of 500 in the AM band?

Q is a measure of the losses. Having a high Q in the coil means the
coil has lower losses. Having a higher Q in the tuning capacitor means
it has lower losses. The lower the losses the more power that ends up
in the headphones.

You have this quite wrong. A Q of 500 is a loss of 0.2%, and
1500 is a loss of only 0.067%. Increase your coil area by 0.13%
(a fraction of a millimeter of diameter) and you recover the
power you lost by "only" having a Q of 500, by gathering more
power to start with.

Furthermore, because the signal of interest spreads +-5Khz or so,
when you use a super high Q, you *reject* the parts of the signal
that are outside the passband. So yeah, you get more voltage for
for the low audio frequencies, but *less power overall*.

Duh. Doesn't sound like such a good deal now, does it?

You trimmed the part of my post that dealt with the bandwidth issue. Why
don't you read that again?

Because you said 10KHz, when your bandwidth is nothing like that.
I just couldn't be bothered to call you on all your
lie^H^H^Halternative facts

Why are you here? You aren't interested in discussing anything. You
just want to make drama.

--

Rick C

 

On Mon, 27 Mar 2017 23:47:00 -0400, rickman <gnuarm@gmail.com> wrote:

On 3/27/2017 12:22 PM, Joerg wrote:
On 2017-03-27 07:59, rickman wrote:
On 3/27/2017 10:46 AM, Joerg wrote:

The Q is over 500. It was claimed in this thread that PVC is not
suitable as coil winding material and this proves that it is quite
suitable. Which I already knew because I've used it in RF power amps
decades ago.

Again, context. You are living in a different world. PVC is *not*
suitable in the crystal radio world because there are *much* better
materials. If PVC was the only material available it would be a *great*
coil support. If mud was the only material available it would be a
*great* coil support.


Can you explain why one even want a Q in excess of 500 in the AM band?

That is the _unloaded_ Qu. Still 500 sounds excessive high for
ordinary LC circuits or loop antennas. At higher frequencies a silver
coated cavity resonator would easily ac hive that.

Q is a measure of the losses. Having a high Q in the coil means the
coil has lower losses. Having a higher Q in the tuning capacitor means
it has lower losses. The lower the losses the more power that ends up
in the headphones.

When you connect the load you get the _loaded_ Ql. This Ql determines
the actual receiver bandwidth. For AM reception a 10 kHz bandwidth
would be desirable, so at 1 MHz the loaded Ql=100 would be suitable.

The Qu/Ql ratio determines the signal losses. a Qu/Ql=10:1 gives less
than 1 dB losses, a 2:1 ratio and the loss is a few decibels. A
500/100 ratio gives about 2 dB losses. In receivers with
amplification, this loss is directly added to the noise figure. For
this reason, it is undesirable to have too high loaded Ql in front of
the first amplifier stage. On the other hand, a wide front end can
easily overload the first amplifier or mixer. A high Ql filter between
the first amplifier and mixer helps a lot. This is an issue on VHF and
above.

The Q of the radio won't be the same as the Q of the components because
you are sucking off power to drive the headphones. Besides, the number
you came up with (10 kHz) would be perfect for AM radio if you can get
that, that is the channel spacing. Great selectivity.

It should be noted that BW = f / Q only gives the -3 dB point of the
response curve. There might be a 40-60 dB signal on the adjacent
channel, which will effectively kill the reception of the wanted
signal.

 

[Sylvia Else]

On 28/03/2017 6:39 PM, piglet wrote:

On 28/03/2017 02:03, Sylvia Else wrote:
On 28/03/2017 10:25 AM, Jim Thompson wrote:

http://www.analog-innovations.com/SED/CD-Ignition-Basic.pdf

http://www.analog-innovations.com/SED/CDI_Inductor.jpg> ...Jim
Thompson


Don't quite see how that works - does it rely on the reverse breakdown
of D3?

Sylvia.


D3 acts normally, the output is a large negative spike.

piglet

Yes, I see it now.

Sylvia.

 

On Tue, 28 Mar 2017 10:16:48 +1100, Clifford Heath
<no.spam@please.net> wrote:

On 27/03/17 23:25, amdx wrote:
On 3/27/2017 6:57 AM, Tauno Voipio wrote:
Joerg, you seem not understand the innermost sense of the crystal-
radio people. They are closely related to audiophools, and it is
quite impossible to use sensible technical argumentation here.

I don't get that at all, can you back that up with any facts?

~1MHz, Q=500, bandwidth ~ 2KHz. Remind me why you need Q>1500?
More voltage does not create better audio.

That is the unloaded Q (Qu).

The loaded Q (Ql) determines the bandwidth, when a load (such as an
amplifier stage or headphones) take out energy from the resonator.

 

[Tauno Voipio]

On 28.3.17 06:33, rickman wrote:

Again, you are not speaking from knowledge. There are ham radio
antennas with exactly this sort of high Q and they manage to maintain
tuning during 100 watt transmissions.

Why are you guys trying to discuss a topic you actually know little about.

There are cases where the Q of the tuner and antenna combination
restricted the way the transmission can be modulated.

In aviation, there are non-directional beacons (NDB) working
in the MF range. Due to obvious mechanical restrictions, the
vertical antennas are very short compared to the wavelength
(70 ft compared to 4000 ft). We had to limit the frequency
of the AM modulated identifier Morse code from the standard
1050 Hz to 400 Hz to pass the bandwidth of the antenna system.

And yes, there was some power, typically 500W into the antenna
and a couple of W into the air.

--

-TV

 

[Clifford Heath]

On 28/03/17 19:35, rickman wrote:

On 3/28/2017 4:07 AM, Clifford Heath wrote:
On 28/03/17 18:42, rickman wrote:
On 3/28/2017 3:15 AM, Clifford Heath wrote:
On 28/03/17 14:47, rickman wrote:
On 3/27/2017 12:22 PM, Joerg wrote:
On 2017-03-27 07:59, rickman wrote:
On 3/27/2017 10:46 AM, Joerg wrote:

The Q is over 500. It was claimed in this thread that PVC is not
suitable as coil winding material and this proves that it is quite
suitable. Which I already knew because I've used it in RF power
amps
decades ago.

Again, context. You are living in a different world. PVC is *not*
suitable in the crystal radio world because there are *much* better
materials. If PVC was the only material available it would be a
*great*
coil support. If mud was the only material available it would be a
*great* coil support.


Can you explain why one even want a Q in excess of 500 in the AM
band?

Q is a measure of the losses. Having a high Q in the coil means the
coil has lower losses. Having a higher Q in the tuning capacitor
means
it has lower losses. The lower the losses the more power that ends up
in the headphones.

You have this quite wrong. A Q of 500 is a loss of 0.2%, and
1500 is a loss of only 0.067%. Increase your coil area by 0.13%
(a fraction of a millimeter of diameter) and you recover the
power you lost by "only" having a Q of 500, by gathering more
power to start with.

Furthermore, because the signal of interest spreads +-5Khz or so,
when you use a super high Q, you *reject* the parts of the signal
that are outside the passband. So yeah, you get more voltage for
for the low audio frequencies, but *less power overall*.

Duh. Doesn't sound like such a good deal now, does it?

You trimmed the part of my post that dealt with the bandwidth issue. Why
don't you read that again?

Because you said 10KHz, when your bandwidth is nothing like that.
I just couldn't be bothered to call you on all your
lie^H^H^Halternative facts

Why are you here? You aren't interested in discussing anything. You
just want to make drama.

I'm sorry you're so confused by facts, but I'm not responsible for
fixing your innumeracy. I'll just get the popcorn and watch while you
chase unicorns.

 

On Tuesday, March 28, 2017 at 11:04:10 AM UTC-4, Phil Hobbs wrote:

It's funny to see so much emotion over somebody else's hobby circuit.
Building the ultimate crystal set is like making an oscillator that will
run on a 5-mV supply.

Certainly! For example,

+0.35v @ 150pA
-+-
|
+-------+---------+------.
| | | |
2.2G 22G 22G 2.2G
| | | |
| 10pF | | 10pF|
+---||--+--. .--+--||--+------+---> 3.2Hz
| \ / | |
| / | 10pF Cload
\| / \ |/ |
Q1 |--------' '-------| Q2 ===
.<| |>. GND
| |
=== Q1-2 = 2n5089 ===
GND GND

A very silly oscillator

Dissipation: 55pW

It's not good for much, but it can be a lot of
fun if you have time on your hands and nothing to prove.

Au contraire! This basic astable forms the foundation for a 3.2Hz
micro^H^H^H^Hacrocontroller, with applications for personal space
travel, over-unity energy devices, and reversing global warming.

I can see the fun of trying to make the highest-Q coil you can, just as
I can see the beauty of shiny silver-plated air variable caps.

Think stamp collecting, not designing for 1e6 units.

Cheers

Phil Hobbs

(Who once built a completely impractical capacitive gauge that was
linear to 0.2% right down to where the plates touched. Nice polished
brass things they were, too.)

Cheers,
James Arthur

(Who once designed a modestly hi-Z amplifier for some crystal radio
buffs.
(A work still in progress.)

 

[Joerg]

On 2017-03-28 02:51, upsidedown@downunder.com wrote:

On Mon, 27 Mar 2017 23:47:00 -0400, rickman <gnuarm@gmail.com> wrote:

On 3/27/2017 12:22 PM, Joerg wrote:
On 2017-03-27 07:59, rickman wrote:
On 3/27/2017 10:46 AM, Joerg wrote:

The Q is over 500. It was claimed in this thread that PVC is not
suitable as coil winding material and this proves that it is quite
suitable. Which I already knew because I've used it in RF power amps
decades ago.

Again, context. You are living in a different world. PVC is *not*
suitable in the crystal radio world because there are *much* better
materials. If PVC was the only material available it would be a *great*
coil support. If mud was the only material available it would be a
*great* coil support.


Can you explain why one even want a Q in excess of 500 in the AM band?

That is the _unloaded_ Qu. Still 500 sounds excessive high for
ordinary LC circuits or loop antennas. At higher frequencies a silver
coated cavity resonator would easily ac hive that.

Q is a measure of the losses. Having a high Q in the coil means the
coil has lower losses. Having a higher Q in the tuning capacitor means
it has lower losses. The lower the losses the more power that ends up
in the headphones.

When you connect the load you get the _loaded_ Ql. This Ql determines
the actual receiver bandwidth. For AM reception a 10 kHz bandwidth
would be desirable, so at 1 MHz the loaded Ql=100 would be suitable.

Exactly, not 500 or 1000. Still, even with a somewhat matching loaded Q
the audio quality is mediocre because a simple tuned circuit has a poor
shape factor. This results in higher audio frequencies being muffled,
speech to be less easy to understand and as you said further below a
strong station on the next AM channel will spoil the whole experience by
swamping the signal.

The Qu/Ql ratio determines the signal losses. a Qu/Ql=10:1 gives less
than 1 dB losses, a 2:1 ratio and the loss is a few decibels. A
500/100 ratio gives about 2 dB losses.

Which is close to impossible to even hear.

... In receivers with
amplification, this loss is directly added to the noise figure. For
this reason, it is undesirable to have too high loaded Ql in front of
the first amplifier stage. On the other hand, a wide front end can
easily overload the first amplifier or mixer. A high Ql filter between
the first amplifier and mixer helps a lot. This is an issue on VHF and
above.


The Q of the radio won't be the same as the Q of the components because
you are sucking off power to drive the headphones. Besides, the number
you came up with (10 kHz) would be perfect for AM radio if you can get
that, that is the channel spacing. Great selectivity.
It should be noted that BW = f / Q only gives the -3 dB point of the
response curve. There might be a 40-60 dB signal on the adjacent
channel, which will effectively kill the reception of the wanted
signal.

There is probably some sort of sports ambition where the guy with the
highest Q wins a trophy or at least a free beer

--
Regards, Joerg

http://www.analogconsultants.com/