[Scan-DC] 137-138 MHz satellites?

[Jeff Krauss]

Orbcomm seems to have a 50 kHz downlink feeder link channel centered 
on 137.56 MHz.
NOAA may also operate a satellite system that uses the 137-38 MHz band.


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>
>Message: 10
>Date: Thu, 11 Jun 2009 20:40:33 -0400
>From: "Andrew Clegg" <w4jecom at w4je.com>
>Subject: [Scan-DC] 137-138 MHz satellites?
>To: <Scan-DC at mailman.qth.net>
>Message-ID: <2E0A2AEA86BB4EDEBC40BADE46B625F7 at CleggHome>
>Content-Type: text/plain; format=flowed; charset="iso-8859-1";
>         reply-type=original
>
>I've been recording some waterfall plots of the 137 - 138 MHz satellite
>downlink band with my HP spectrum analyzer today. I looked back through the
>data recorded while I was at work, and it appears I caught several
>narrowband signals throughout the band, and one relatively strong broadband
>signal near the top of the band. This is just with a discone, and without
>any pre-amp, so the signals must be fairly strong (for satellites) to show
>up directly on the specan, given the lousy noise figure. The signals come
>and go consistent with the ~few minute pass of a LEO satellite, so I believe
>they are real, although I can't yet be certain. They should be easily heard
>on my receiver, or even a regular scanner with a decent antenna.
>
>I suspect the narrowband signals are Orbcomm. Does anyone have any current
>active downlink frequencies for that sytem? The waterfall plot resolution is
>not quite good enough to assign a reliable frequency to the signals. I'd
>like to try to record their sounds. Online references all seem to be quite
>old. The approximate frequencies I captured are:
>
>137.244
>137.311
>137.379
>137.404
>137.450
>137.502
>137.726
>137.731
>137.750
>
>These are all +/- few kHz due to the resolution of the plots. The 137.726 &
>137.731 signals could be one in the same.
>
>Does anyone know of any other confirmed active satellites in this band
>besides Orbcomm, and their freqs? Any idea what the broadband satellite
>might have been? Based on the data, it looks like two peaks, each of  ~25 -
>40 kHz wide, one centered ~ 137.94, and the other ~137.98. It was visible
>from ~11:42 AM - 11:45 AM, with a definite peak amplitude ~11:44 AM (all
>EDT, from Arlington VA), and then quite a bit weaker ~11:55 - 11:58 AM. It's
>possible that this was an overhead pass, and my antenna, which has better
>gain toward the horizon than straight up, caught the signal best when rising
>and setting. A similar signal was seen again, but much weaker, around 12:59
>PM, which would be too soon to be the same satellite passing again. Those
>were the only broadband "passes" from 8 am to 3 pm. (Then again, this could
>be something other than a satellite, but the allocation for this band is all
>satellite downlinks).
>
>Any specific frequency info on currently active satellites in this band
>would be appreciated!
>
>Cheers,
>Andy
>
>
>
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