On 7/30/2014 5:08 PM, Lostgallifreyan wrote:
Jerry Stuckle wrote in news:lrbmkt$ohq$1@dont-
email.me:

Not necessarily. Even if there were physical vibrations, they may be
out of the audible range. But even vibrations are not common. You were
lucky you could hear it.


Well, it was like a flanger having a psychedilc fit. Hard to ignore!
Fortunately easy to cure. I imagine that many other sources of wild RF
oscillation might affect the sound like that.


Not really. To affect the sound, you need something which will respond
to the RF in a physical vibration manner (i.e. magnetic), and the signal
must be in the audio spectrum.

Neither is very likely.

--
==================
Remove the "x" from my email address
Jerry Stuckle

==================

Jerry Stuckle wrote in news:lrcavl$dok$2@dont-
email.me:

On 7/30/2014 5:08 PM, Lostgallifreyan wrote:
Jerry Stuckle wrote in news:lrbmkt$ohq$1@dont-
email.me:

Not necessarily. Even if there were physical vibrations, they may be
out of the audible range. But even vibrations are not common. You were
lucky you could hear it.


Well, it was like a flanger having a psychedilc fit. Hard to ignore!
Fortunately easy to cure. I imagine that many other sources of wild RF
oscillation might affect the sound like that.


Not really. To affect the sound, you need something which will respond
to the RF in a physical vibration manner (i.e. magnetic), and the signal
must be in the audio spectrum.

Neither is very likely.


To produce audio from RF directly all that is needed is for the difference (a
beat frequency) to fall within the audio pass band of the equipment. A wildly
varying frequency of oscillation could make a sweep of audio pitch. Timbre or
variability of effect might give plenty of clues as to cause. That's what led
me to find and fix the original oscillations in the dodgy ground plane
connection in the preamp casing. If it can happen this way on one (tiny)
scale, I see no general reason why it could not happen on the larger scale
with feedback between antennas a hundred feet apart. Whether I can use it
diagnostically is questionable, but I think it can exist. Given the number of
frequencies picked up by the antenna, I find it hard to beleive that NO stray
feedback oscillation would differ from any one of them by a value that puts
it in the audio band. I'm fairly sure I'd hear something, especially if
choosing a clean audio signal over which it woudl easily show up.

On 7/31/2014 3:36 AM, Lostgallifreyan wrote:
Jerry Stuckle wrote in news:lrcavl$dok$2@dont-
email.me:

On 7/30/2014 5:08 PM, Lostgallifreyan wrote:
Jerry Stuckle wrote in news:lrbmkt$ohq$1@dont-
email.me:

Not necessarily. Even if there were physical vibrations, they may be
out of the audible range. But even vibrations are not common. You were
lucky you could hear it.


Well, it was like a flanger having a psychedilc fit. Hard to ignore!
Fortunately easy to cure. I imagine that many other sources of wild RF
oscillation might affect the sound like that.


Not really. To affect the sound, you need something which will respond
to the RF in a physical vibration manner (i.e. magnetic), and the signal
must be in the audio spectrum.

Neither is very likely.


To produce audio from RF directly all that is needed is for the difference (a
beat frequency) to fall within the audio pass band of the equipment. A wildly
varying frequency of oscillation could make a sweep of audio pitch. Timbre or
variability of effect might give plenty of clues as to cause. That's what led
me to find and fix the original oscillations in the dodgy ground plane
connection in the preamp casing. If it can happen this way on one (tiny)
scale, I see no general reason why it could not happen on the larger scale
with feedback between antennas a hundred feet apart. Whether I can use it
diagnostically is questionable, but I think it can exist. Given the number of
frequencies picked up by the antenna, I find it hard to beleive that NO stray
feedback oscillation would differ from any one of them by a value that puts
it in the audio band. I'm fairly sure I'd hear something, especially if
choosing a clean audio signal over which it woudl easily show up.


Yes, I know how it works - I've held both amateur and commercial
licenses for well over 40 years and worked on almost everything from $40
CB sets to multimillion dollar mainframe computers. I've even done some
design in my free time. I suggest you not try to teach those who know
more than you your "facts".

The facts a to have the beat frequency, you need two signals within
15kHz or so of each other. Those signals must be mixed, which means at
least one must be non-linear. This will give you a beat frequency in
the audio spectrum.

Once you have this, you need something to generate a strong enough
magnetic field in the audio frequency range to act as a driver, and
something close enough and made of a magnetic material to vibrate.

I've seen a fair number of spurious emissions over the years (mostly
from VHF/UHF radios). Every one of them has been RF, and none of them
have created audio oscillations.

A few months ago we even had a case right here where a VHF radio in a
county bus had a spur on the input to the local 2 meter ham repeater.
Once again, no indication in the bus this was occurring. The county
found out about it only after the hams contacted them.

--
==================
Remove the "x" from my email address
Jerry, AI0K

==================

Jerry Stuckle wrote in news:lrdc2v$b15$1@dont-
email.me:

The facts a to have the beat frequency, you need two signals within
15kHz or so of each other. Those signals must be mixed, which means at
least one must be non-linear. This will give you a beat frequency in
the audio spectrum.


Ok, that nonlinear bit makes sense. If the signals do not do that then I'd
have nothing to detect the way I heard it. When I said audio I didn't mean
direct emission from something driven by strong RF. I was thinking it might
be heard from a weak signal added to the output audio signal, as happened
with that preamp's casing before I improved its connection to the PCB's
ground plane. The sound was a kind of whistling squeal, almost white-noise at
times. I imagined that feedbacking antennas might also produce this, and
that's the core of my question, whether or not this is true, or useful even
if it is.

By the way, I'm not trying to teach you anything. I know you know these
things or I'd not be here asking stuff. I was just stating what I know to try
to get to the bottom of this, and so you had some basis for pitching a reply
based on what you have reason to think I might understand.

On 7/31/2014 3:39 PM, Lostgallifreyan wrote:
Jerry Stuckle wrote in news:lrdc2v$b15$1@dont-
email.me:

The facts a to have the beat frequency, you need two signals within
15kHz or so of each other. Those signals must be mixed, which means at
least one must be non-linear. This will give you a beat frequency in
the audio spectrum.


Ok, that nonlinear bit makes sense. If the signals do not do that then I'd
have nothing to detect the way I heard it. When I said audio I didn't mean
direct emission from something driven by strong RF. I was thinking it might
be heard from a weak signal added to the output audio signal, as happened
with that preamp's casing before I improved its connection to the PCB's
ground plane. The sound was a kind of whistling squeal, almost white-noise at
times. I imagined that feedbacking antennas might also produce this, and
that's the core of my question, whether or not this is true, or useful even
if it is.

By the way, I'm not trying to teach you anything. I know you know these
things or I'd not be here asking stuff. I was just stating what I know to try
to get to the bottom of this, and so you had some basis for pitching a reply
based on what you have reason to think I might understand.


Even if it were a weak signal added to the audio output, chances are you
wouldn't hear it. As I said before - you were very lucky to hear the
squeal before; very few spurious radiations will have any audio component.

And BTW - your problem with the ground plane was probably corrosion in
the connection, causing the RF to be rectified. But even then,
generally it will not be in the audible frequency range.

--
==================
Remove the "x" from my email address
Jerry, AI0K

==================

Jerry Stuckle wrote in news:lre73e$jps$1@dont-
email.me:

Even if it were a weak signal added to the audio output, chances are you
wouldn't hear it. As I said before - you were very lucky to hear the
squeal before; very few spurious radiations will have any audio component.

And BTW - your problem with the ground plane was probably corrosion in
the connection, causing the RF to be rectified. But even then,
generally it will not be in the audible frequency range.


Agreed, even the thin oxide layer on the aluminium when new was enough
corrosion. Also, not enough points of contact around the edges of the board
before I fixed it.

About 'lucky', maybe. The rason I brought it up was because the sound WAS
so white-noise like. It seemed to imply a scatter so broad that a careful ear
might detect a far lesser version of the effect.

On Thu, 31 Jul 2014 08:16:29 -0400, Jerry Stuckle
wrote:

Yes, I know how it works - I've held both amateur and commercial
licenses for well over 40 years and worked on almost everything from $40
CB sets to multimillion dollar mainframe computers.

Well let's see... I got my novice license when I was 15, so that means
I've had a ham license (various call signs) for 51 years. My FCC
First Class and now GROL for about 46 years.

I've even done some design in my free time.

My time is not free. I did RF design and ran a 2way shop for about 11
years. I guess that having more years of experience entitles me to
tell you how to run your life.

I suggest you not try to teach those who know
more than you your "facts".

Yep. Quantity is a good substitute for quality. Unfortunately, I
have to agree with most of your comments.

The facts a to have the beat frequency, you need two signals within
15kHz or so of each other. Those signals must be mixed, which means at
least one must be non-linear.

Signals are not linear or non-linear, but are usually called
"distorted" if not a clean sine wave. The circuitry through which the
signals pass can be linear or non-linear. Linear circuits do not mix,
unless overloaded. If the mixing circuit is non-linear, you can use
harmonics to create more mix combinations that result in 15KHz
frequency difference.
n*f1 +/- m*f2 = beat_freq
where n and m are integers.

This will give you a beat frequency in
the audio spectrum.

Yep. However, my hearing is kinda marginal and needs something lower
than about 10-12KHz.

Once you have this, you need something to generate a strong enough
magnetic field in the audio frequency range to act as a driver, and
something close enough and made of a magnetic material to vibrate.

True. There has to be an electric to audio transducer somewhere.
However, there are situations where the mechanism is obscure. For
example, when I moved into my house in Ben Lomond in 1973, the 200MHz
radar on nearby Mt Umunhum was running megawatts pointed straight at
me. Every time the rotating dish went by, my hi-fi would produce buzz
out of the speakers at the pulse repetition frequency. That was easy
enough to understand. However, the coils inside my kitchen electric
oven also went twang as the beam went by, which was more difficult to
explain. There had to be a rusty connection or bolt, but I couldn't
find one. Maybe the oven or coils were resonant at 200 Mhz. I never
did figure out how it worked.

I've seen a fair number of spurious emissions over the years (mostly
from VHF/UHF radios). Every one of them has been RF, and none of them
have created audio oscillations.

When I transmit on my VHF HT near my comptah speakers, they buzz
loudly. Does that count?

A few months ago we even had a case right here where a VHF radio in a
county bus had a spur on the input to the local 2 meter ham repeater.
Once again, no indication in the bus this was occurring. The county
found out about it only after the hams contacted them.

The county should have had a new digital or narrow band radio. Was
this a new radio? I usually look at the output on a spectrum analyzer
before letting something go out the door.

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

On 7/31/2014 7:29 PM, Jeff Liebermann wrote:
On Thu, 31 Jul 2014 08:16:29 -0400, Jerry Stuckle
wrote:

Yes, I know how it works - I've held both amateur and commercial
licenses for well over 40 years and worked on almost everything from $40
CB sets to multimillion dollar mainframe computers.

Well let's see... I got my novice license when I was 15, so that means
I've had a ham license (various call signs) for 51 years. My FCC
First Class and now GROL for about 46 years.

I've even done some design in my free time.

My time is not free. I did RF design and ran a 2way shop for about 11
years. I guess that having more years of experience entitles me to
tell you how to run your life.

I suggest you not try to teach those who know
more than you your "facts".

Yep. Quantity is a good substitute for quality. Unfortunately, I
have to agree with most of your comments.


True. Fortunately, all of my experience has been "quality".

The facts a to have the beat frequency, you need two signals within
15kHz or so of each other. Those signals must be mixed, which means at
least one must be non-linear.

Signals are not linear or non-linear, but are usually called
"distorted" if not a clean sine wave. The circuitry through which the
signals pass can be linear or non-linear. Linear circuits do not mix,
unless overloaded. If the mixing circuit is non-linear, you can use
harmonics to create more mix combinations that result in 15KHz
frequency difference.
n*f1 +/- m*f2 = beat_freq
where n and m are integers.


Just because a signal is not a sine wave does not mean it is distorted.
A mix of several different frequencies (i.e. music, voice) produces
something far from resembling a sine wave - but it is not distorted. I
won't get into the math here - but there is a solid foundation.

And if a linear circuit is overloaded, it is no longer linear.
Harmonics may or may not come into play - it all depends on the
characteristics of the circuit. For instance, the harmonics of an FM
band (88-106 MHz) amplifier are nowhere near the audio range. And mix
combinations are even less likely to be anywhere near the audio range.

This will give you a beat frequency in
the audio spectrum.

Yep. However, my hearing is kinda marginal and needs something lower
than about 10-12KHz.


Audio range is generally considered to be 20Hz - 15Khz. But that is a
general range; individual people can have greater or lesser ranges.

Once you have this, you need something to generate a strong enough
magnetic field in the audio frequency range to act as a driver, and
something close enough and made of a magnetic material to vibrate.

True. There has to be an electric to audio transducer somewhere.
However, there are situations where the mechanism is obscure. For
example, when I moved into my house in Ben Lomond in 1973, the 200MHz
radar on nearby Mt Umunhum was running megawatts pointed straight at
me. Every time the rotating dish went by, my hi-fi would produce buzz
out of the speakers at the pulse repetition frequency. That was easy
enough to understand. However, the coils inside my kitchen electric
oven also went twang as the beam went by, which was more difficult to
explain. There had to be a rusty connection or bolt, but I couldn't
find one. Maybe the oven or coils were resonant at 200 Mhz. I never
did figure out how it worked.


Could be - but what was radar doing at 200Mhz? Not only will it
interfere with both business band and amateur frequencies, but the large
beam width would make it pretty useless. And as weather radar, it would
be useless.

I've seen a fair number of spurious emissions over the years (mostly
from VHF/UHF radios). Every one of them has been RF, and none of them
have created audio oscillations.

When I transmit on my VHF HT near my comptah speakers, they buzz
loudly. Does that count?


Whatever trips your trigger.

A few months ago we even had a case right here where a VHF radio in a
county bus had a spur on the input to the local 2 meter ham repeater.
Once again, no indication in the bus this was occurring. The county
found out about it only after the hams contacted them.

The county should have had a new digital or narrow band radio. Was
this a new radio? I usually look at the output on a spectrum analyzer
before letting something go out the door.


This is an 800 Mhz radio, not VHF. Only the spur was on VHF.

But then it appears you're just trolling like you usually do. The
difference is this time I'm not going to fall for it. You can have the
last word.

--
==================
Remove the "x" from my email address
Jerry, AI0K

==================

On Thu, 31 Jul 2014 20:34:32 -0400, Jerry Stuckle
wrote:

Could be - but what was radar doing at 200Mhz? Not only will it
interfere with both business band and amateur frequencies, but the large
beam width would make it pretty useless. And as weather radar, it would
be useless.

Left over from the cold war. Someone forgot to turn it off or
something.

214-236 Mhz. Not sure about the pulse repetition frequency but it had
to be fairly low audio frequency in order to obtain the long range. At
3500ft elevation, the radar range is 84 miles.

Some of the URL's below show 420 to 450 MHz for the AN/FPS-24. That's
wrong for the early models. Built in 1957 and pulled the plug in
1980:
http://en.wikipedia.org/wiki/Mount_Umunhum
http://en.wikipedia.org/wiki/AN/FPS-24
http://www.radomes.org/museum/equip/fps-35.html
https://www.google.com/search?q=mt+umunhum+radar&tbm=isch
https://www.youtube.com/watch?v=nqfsWBZR8XM
I can see the building through the trees from my house. Amazing what
5 megawatts can do.

The dish rotated at the then standard rate of two revolutions per
minute. So, every 30 seconds, there was a blast of buzz from the
hi-fi, 2way, phone, and oven (I didn't have a TV back then). I
learned to automatically stop talking just before the bzzzzzt, and
continue talking after it was gone in about one second. When they
pulled the plug in 1980, I continued to do this unconsciously for
several months. Incidentally, I tried bypasses and ferrite beads.
They helped, but didn't totally eliminate the buzz. Transcribing
vinyl records to 1/4" tape was a lost cause.



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

On 7/31/2014 7:29 PM, Jeff Liebermann wrote:

My time is not free. I did RF design and ran a 2way shop for about 11
years. I guess that having more years of experience entitles me to
tell you how to run your life.


I should also add - "ran a 2way shop for about 11 years". That hardly
qualifies you as an "expert". As for "RF design" - what did you design
- TV amplifiers?

And I never said my time was free - I said in my free time. It's a
hobby I enjoy. But trolls don't understand that.

Again - I'm not falling for your trolling again - you can have the last
word.

--
==================
Remove the "x" from my email address
Jerry Stuckle

==================