[amsat-bb] Re: Terrestrial QRM to FM satellites

[Ernie Howard]

It seems that we have been down this road before......

The short data burst is not paging. The 'squawk' that seems to be at the end 
of the 'offenders' individual transmissions in the first part of the clip is 
recognizable to me. It is 1200 baud, and from the sound/duration it is 
Motorola MDC1200 coding. The MDC1200 is used for ID and status on public 
safety and other systems. Several hams in my area have taken to using the 
Motorola radios with the MDC1200 system to ID and contact each other 
(selective calling, status, emergency, etc.). It is not likely that it would 
give us much info to go on, if we could decode it. The MDC 1200 system uses 
hex number data, it is not ASCII. The data, when decoded on another radio 
will be a 4 digit number. There is a short write up (and sound samples) on:
http://en.wikipedia.org/wiki/MDC-1200

Another possibility is that someone has established a simplex Echolink 
system on the uplink. That may be why some have reported a CW id, and the 
carrier hanging on for longer than a normal simplex transmission.

Perhaps someone with AMSAT could contact the ARRL Official Observer 
coordinator. They have been known to send out requests for the OO corps to 
listen for specific interference problems. This might be important enough to 
get all ears listening. I don't hear it here.

73 Ernie W8EH


Bruce Robertson wrote:

 > Once I started hearing this QRM while listening to AO-27, I recorded the
 > tail-end of the 20:00Z pass. Interested persons may download a mp3 file at
 > http://heml.mta.ca/Amsat/ (There is no promise that this link will be in
 > place for a long time.)
 >
 > Besides the beeps and long periods of carrier-induced silence, there are
 > some conversational snippets which seem to me from native English speakers.
 > One of the amateurs on the bird suggested the QRM comes from a pager, and I
 > labeled the file as such, but I don't mean to suggest that this
 > identification is secure.


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Ernie Howard, Jr    W8EH    Middletown, Ohio
E-mail: w8eh at arrl.net
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