[Scan-DC] More signals, this time ~400 MHz

[Andrew Clegg]

For what it's worth, I've now also captured Orbcomm signals in the 400.1 MHz 
region. My coax loss is a bit larger there, but the signals are definitely 
there, with the characteristic Doppler "s-curve".

I'm listening to the whole 399.9 - 406.1 MHz band now. That region is 
allocated for radiosondes and some satellite downlinks/uplinks. I think I 
may be capturing some radiosonde data transmissions in the 401.75 MHz 
region. I know that weather balloons are often sent up around sunrise and 
sunset, so that may be what I'm hearing, but I'll have to build up some 
statistics to see if the signals have any pattern. Until about ten minutes 
ago, there was a pair of signals, each with ~2 minute long bursts, every 
four or five minutes. Whoops, ~401.768 just became active again. I'll have 
to poke around the net and see if I can find who this might belong to. If 
anyone knows, chime in!

A couple of years ago, I had my telescope set up on my balcony right around 
sunset, and I noticed a very bright star-like object in the west, but it was 
steadily moving upward. It was about -1 magnitude, or about as bright at 
Jupiter. It was not moving like a plane or a satellite (or an Iridium 
flare). I managed to track it with my scope for a few minutes, and it was 
basically a big shiny disk, slightly elongated. I believe it was a weather 
balloon, but I was surprised that one would be launched in a busy air 
traffic area like DC.

Cheers,
Andy



----- Original Message ----- 
From: "Andrew Clegg" <w4jecom at w4je.com>
To: "David I. Emery" <die at dieconsulting.com>
Cc: <Scan-DC at mailman.qth.net>
Sent: Saturday, June 13, 2009 10:51 PM
Subject: Re: [Scan-DC] 137-138 MHz satellites?


>I just added a Mini-Circuits pre-amp and the signals are much stronger. 
>They
> definitely have the Doppler signature to them, so I have confirmed they 
> are
> satellites. (Mini-Circuits makes great stuff!)
>
> Andy
>
>
> ----- Original Message ----- 
> From: "David I. Emery" <die at dieconsulting.com>
> To: "Andrew Clegg" <w4jecom at w4je.com>
> Cc: <Scan-DC at mailman.qth.net>
> Sent: Saturday, June 13, 2009 1:43 AM
> Subject: Re: [Scan-DC] 137-138 MHz satellites?
>
>
>> On Thu, Jun 11, 2009 at 08:40:33PM -0400, Andrew Clegg wrote:
>>> 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.
>>
>> You should also see doppler on any satellite based signals.
>> On a waterfall this will result in a tilt rather than straight line
>> plot.
>>
>>
>> -- 
>>  Dave Emery N1PRE/AE, die at dieconsulting.com  DIE Consulting, Weston, Mass
>> 02493
>> "An empty zombie mind with a forlorn barely readable weatherbeaten
>> 'For Rent' sign still vainly flapping outside on the weed encrusted 
>> pole -
>> in
>> celebration of what could have been, but wasn't and is not to be now
>> either."
>>
>>
>
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