[MilCom] Signal Mystery 243.00!

[Duane Mantick]

 If you get it on one brand of radio but not another I would be
suspicious that it was a "birdie" that was common to the Uniden
design.  BUT - if you've been around radios long enough you 
know that "weird stuff happens".  My suggestion would be to go
back on a weekend or whenever you have more time, and armed with
a bunch of receivers as well as a freq. counter if you have one
and snoop the thing out as close as you can get.  If some security
guard tells you to leave, well, you're stuck with that.

Most of the time that sort of stuff isn't worth worrying about
but given the frequency you have listed of 243.00 it is probably
worth investigating.  If something in a factory or warehouse
happens to be accidentally emitting on that frequency for real
and you can reliably sniff it out, you might be doing a lot of
people a favor even though they might not see it that way when you
first approach them about it.  :-)

There are a LOT of possible scenarios IFFFFF the signal isn't just a 
"birdie" in your Uniden radios.  First off, that's exactly double
121.5 which is the civilian aircraft emergency channel - that is
another one that someone really doesn't want to be radiating.  Half
again is 60.75 MHz - don't know what might be assigned there.  If what
[although thinking about it tells me it is just above the 6 meter
Ham band which puts it around TV channels 2 and 3]
you're picking up is a harmonic of either 121.5 or 60.75 then that
fundamental must be pretty strong if your 243.00 reads S-5.  It would be
hard to imagine going any further down for a fundamental but the next
even division by two is 30.375.  Check those frequencies and see if
you get anything there.  If you do, then it sounds like something is
"dirty" and needs to be reported.  If not, and 243 is all you get
then work that freq. and "sniff" as close to the offending area as 
you can get.  If you have other scannists in your area that you can 
get to assist, get them out as well and see if THEY pick it up.  If
it is only you and only one radio or one brand of radio, then I'd
say get hold of Uniden - more often than not, they know what "birdie"
frequencies they have.  They may not want to admit it or tell you....
but some of these companies used to even publish them right in the
owner's manuals.  I think Radio Shack did on the 2004/5/6 series but
I'd have to look back on that to be sure and I know I have seen others
right in the Owner's manuals.

I seem to recall a story lately out of the UK where some electronic
device was radiating on 121.5 and triggered a SAR mission.  I'll bet
somebody got reamed on that one, if true.  I think there have been
cases here in the US of similar occurrences where a defective device
just by fluke happened to radiate on 121.5 and got plenty of attention.
If NOT a "birdie", you could be doing somebody a big, BIG favor.

A lot of electronics these days are cheaply made with very little 
attention to Part 15 emissions;  in my last job I had a customer
complaining about short range on his garage door openers.  He had two
doors, two openers, two receivers and BOTH of them with the identical
problem.  That told me right away that the odds of both openers being
defective was almost ZERO.  After prying information out of the customer
about any changes to anything electrical in his garage we started switching 
things off.  We killed one circuit and whammo, problem gone.  So we
unplugged everything on that circuit, brought it back live and started
plugging things in, one item at a time.  The culprit turned out to be
a cordless phone but NOT the actual phone but the charger base!  It was
radiating a signal right smack on the garage door opener frequency that
was so strong that it partially dispensed the GDO receivers and thus reduced
the range of opening.  Getting that cordless out of the garage solved the
problem.  So there's a LOT of stuff that you wouldn't ordinarily think
of that can radiate garbage all over the spectrum.

Tracking down true RFI can be a real pain in the butt - while it is 
annoying to have to accept "birdies" in your radios, it is almost 
better than trying to do that tracking....and, if you keep track of them
when you find them with a note in your owners manual and a copy you
carry along with the radios, it can save you a lot of headaches when
you run into one and you wouldn't otherwise have known.

Duane
WB9OMC


-----Original Message-----
From: milcom-bounces at mailman.qth.net [mailto:milcom-bounces at mailman.qth.net]
On Behalf Of Ken
Sent: Saturday, March 04, 2006 2:04 PM
To: MilCom
Subject: [MilCom] Signal Mystery 243.00!

Every day on my way to work mobile with both the BC296D & BC780XLT when I go
by specific area (there's a few commerical buildings) I get a strong signal
(S5) & it appears to be an open mike (unlike cable leakage which has some 
noise and/or actual program (distorted) audio)...     Now is this an image 
and if so any ideas to the actual frequency?  BTW my RS Pro 83 in "signal
stalking" mode, doesn't get a hit.

Ken
Springfield MA Monitoring Area 


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