Reply
 
LinkBack Thread Tools Search this Thread Display Modes
  #1   Report Post  
Old July 30th 14, 02:34 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Oct 2012
Posts: 1,067
Default Indoor FM boost with no cables?

On 7/30/2014 1:16 AM, Lostgallifreyan wrote:
Jerry Stuckle wrote in
:

The problem with what you're trying to do is you can easily get RF
feedback between the output antenna and the input antenna, causing
oscillations. And those oscillations may not be in the FM band - they
may be on an adjacent band (like aircraft, which is just above the FM
band).


That's my main concern, I want it to be well behaved, or it won't happen. It
has simple 1-pole LC filters to limit it to the FM broadcast band, but I will
leave it intact and not cobble it into another purpose because it's very good
at its original intent.

If I do experiment further, it looks like the best thing to watch out for is
any unexpected oscillation frequencies despite its filters (LPF on input, HPF
on output), and deliberately orienting a radiating dipole to minimise
feedback. Is it easy (or possible) to catch clues of such bad behaviour while
listeing using somethign like a Tecsun PL-390 or other radio using those new
DSP IC's? I ask that because they're cheap, easy to get, and fairly
consistent, and include a usefully specified signal strength meter. If so,
what should I consider to be a warnign sign?

But the amplifier you're trying to use is meant to feed a receiver
directly, not another antenna. So output is going to be very low (on
the order of microwatts) - much lower than any amplifier which feeds an
antenna.


Agreed.
I only tried because the last thing I want to do is pollute the spectrum.
Start small...


1-pole LC filters won't be narrow enough to limit potential oscillations
to the FM band. You'll need much more than that.

As for determining whether it is oscillating or not - I wouldn't trust
anything short of a good spectrum analyzer. The signal could be
anywhere (and changing frequency). A spectrum analyzer will still show
it; a receiver won't necessarily.

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

==================
  #2   Report Post  
Old July 30th 14, 10:00 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Sep 2006
Posts: 613
Default Indoor FM boost with no cables?

Jerry Stuckle wrote in news:lras98$ebf$1@dont-
email.me:

As for determining whether it is oscillating or not - I wouldn't trust
anything short of a good spectrum analyzer. The signal could be
anywhere (and changing frequency). A spectrum analyzer will still show
it; a receiver won't necessarily.


No clues at all? I remember when I first set up that little MAR-6 based
preamp, it had some nasty side effects on the sound till I added a springy
ciopper alloy strip to each side on the underside of the board so it bit
gently into the aluminium case when I slid it in to it, finally curing the
local RF oscillations it had before I solved this. I was wondering if similar
audible sounds might be heard as a guide to other, larger scales of local
feedback and oscillation.
  #3   Report Post  
Old July 30th 14, 10:04 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Oct 2012
Posts: 1,067
Default Indoor FM boost with no cables?

On 7/30/2014 5:00 PM, Lostgallifreyan wrote:
Jerry Stuckle wrote in news:lras98$ebf$1@dont-
email.me:

As for determining whether it is oscillating or not - I wouldn't trust
anything short of a good spectrum analyzer. The signal could be
anywhere (and changing frequency). A spectrum analyzer will still show
it; a receiver won't necessarily.


No clues at all? I remember when I first set up that little MAR-6 based
preamp, it had some nasty side effects on the sound till I added a springy
ciopper alloy strip to each side on the underside of the board so it bit
gently into the aluminium case when I slid it in to it, finally curing the
local RF oscillations it had before I solved this. I was wondering if similar
audible sounds might be heard as a guide to other, larger scales of local
feedback and oscillation.


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.

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

==================
  #4   Report Post  
Old July 30th 14, 10:08 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Sep 2006
Posts: 613
Default Indoor FM boost with no cables?

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.
  #5   Report Post  
Old July 31st 14, 03:51 AM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Oct 2012
Posts: 1,067
Default Indoor FM boost with no cables?

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

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


  #6   Report Post  
Old July 31st 14, 08:36 AM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Sep 2006
Posts: 613
Default Indoor FM boost with no cables?

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.

  #7   Report Post  
Old July 31st 14, 01:16 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Oct 2012
Posts: 1,067
Default Indoor FM boost with no cables?

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

==================
Reply
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules

Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
WCBS-FM ralliers get rates boost Mike Terry Broadcasting 1 June 24th 05 05:43 AM
Funding Boost for Radio New Zealand International Bb Shortwave 0 May 18th 04 05:46 AM
Advice Needed: How to boost signal on 2.4 ghz av unit talltorontoguy Equipment 8 January 13th 04 08:26 AM
PrePaid Boost/Nextel Special [email protected] Swap 0 August 16th 03 06:30 PM
FS PRE-PAID BOOST/NEXTEL [email protected] Swap 0 August 11th 03 12:15 AM


All times are GMT +1. The time now is 03:13 AM.

Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
Copyright ©2004-2025 RadioBanter.
The comments are property of their posters.
 

About Us

"It's about Radio"

 

Copyright © 2017