Indoor FM boost with no cables?
 

On 7/31/2014 10:07 AM, Eric Weaver wrote:
On 07/26/2014 09:24 PM, David Platt wrote:

A few years ago I helped chase down a noise source which was wandering
randomly through the 2-meter repeater input sub-band, and causing
prolonged noisy squelch tails on the ends of transmissions on several
different repeaters in the Silicon Valley area....

Reminds me. Some years back I had the duty of fox-hunting a noise
source inside Great Mall of the Bay Area that was throwing noise on
Milpitas PD's receivers. I wandered around the back doors in the south
core with a PD handheld and a scanner. Turns out a Muzak machine's
power supply was doing it. They sent a replacement and the problem was
gone.

Once there was a laundromat in Redwood City whose TV was spewing junk
around 154 MHz, out the antenna port, jamming Fire channels. I don't
recall how that was resolved, whether an amp was installed isolating the
antenna, or they just got the place a new TV.




And of course there's the now infamous hair salon in San Antonio, Tx,
with the fluorescent light ballasts that caused problems to AT&T Cell
phone network (and it seems this is not the only business with this
problem).

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

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

Indoor FM boost with no cables?
 

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.

Indoor FM boost with no cables?
 

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

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

Indoor FM boost with no cables?
 

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.

Indoor FM boost with no cables?
 

On Thu, 31 Jul 2014 10:19:38 -0400, Jerry Stuckle
wrote:

And of course there's the now infamous hair salon in San Antonio, Tx,
with the fluorescent light ballasts that caused problems to AT&T Cell
phone network (and it seems this is not the only business with this
problem).

The hair salon refused to do anything about it so they got a letter
from the FCC.
http://www.commlawblog.com/2013/10/articles/enforcement-activities-fines-f/bulbs-behind-bars-ii-fcc-goes-after-hair-salon-lighting-fixture/
Seems to be a common problem. Here's one in Smog Angeles:
http://www.pcworld.com/article/2095940/la-buildings-lights-interfere-with-cellular-network-fcc-says.html
My guess(tm) is electronic ballasts.

My favorite was GPS interference from TV amplifiers:
http://gpsworld.com/the-hunt-rfi/
I was not involved in either the cause or solution.

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

Indoor FM boost with no cables?
 

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

Indoor FM boost with no cables?
 

On 7/31/2014 7:03 PM, Jeff Liebermann wrote:
On Thu, 31 Jul 2014 10:19:38 -0400, Jerry Stuckle
wrote:

And of course there's the now infamous hair salon in San Antonio, Tx,
with the fluorescent light ballasts that caused problems to AT&T Cell
phone network (and it seems this is not the only business with this
problem).

The hair salon refused to do anything about it so they got a letter
from the FCC.
http://www.commlawblog.com/2013/10/articles/enforcement-activities-fines-f/bulbs-behind-bars-ii-fcc-goes-after-hair-salon-lighting-fixture/
Seems to be a common problem. Here's one in Smog Angeles:
http://www.pcworld.com/article/2095940/la-buildings-lights-interfere-with-cellular-network-fcc-says.html
My guess(tm) is electronic ballasts.


Yes, I know the story, Jeff. That's why I quoted it. And it's not the
only business which has had problems with GE ballasts. GE has claimed
they've fixed the problem with additional filtering. We'll see.

My favorite was GPS interference from TV amplifiers:
http://gpsworld.com/the-hunt-rfi/
I was not involved in either the cause or solution.


This does not surprise me. There have been a number of problems with
such units, typically from overseas. Many of them are sold in the U.S.
without the required FCC Certification - which puts an unwitting owner
at risk as well as those around him/her.

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

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

Indoor FM boost with no cables?
 

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

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

Indoor FM boost with no cables?
 

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

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

Indoor FM boost with no cables?
 

On Thu, 31 Jul 2014 20:24:10 -0400, Jerry Stuckle
wrote:

Yes, I know the story, Jeff. That's why I quoted it. And it's not the
only business which has had problems with GE ballasts. GE has claimed
they've fixed the problem with additional filtering. We'll see.

Here's more on the story on noisy GE electronic ballasts:
http://www.commlawblog.com/2014/02/articles/enforcement-activities-fines-f/bulbs-behind-bars-iii-more-lighting-fixtures-mess-up-mobile-data-service/
However, GE has found that a small number of units of the
2-lamp ballasts identified above that were manufactured
prior to September 19, 2011 have produced unintentional
high-frequency radio emissions that have the potential to
cause interference with certain types of wireless communications.

...the product codes for the problem ballasts were 72262 and 72266.

Note that the bulletin was NOT publicly distributed by GE and that
there was no voluntary recall by GE. Looks like GE has effectively
buried the problem. With only two documented interference complaints,
both with clueless business owners, I don't believe that the FCC has
enough cause to act on the matter. However, I will give GE credit for
somewhat publicly admitting that there was a problem, even if they did
bury it.





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