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

[Andrew Clegg]

Thanks for the details David. I am going to sort though my data when I get
home tonight and see what I caught. By late last night, those intermittent
data signals at ~401.75 MHz were still there, and the same strength, so I
don't think they are radiosondes after all. They have no Doppler signature,
so they aren't satellites. They could be ground-based radiosonde stations or
satellite uplink Earth stations, according to the allocation table. Or they
could be almost anything, operating with a waiver to the allocation table
(after all, Orbcomm itself must have received a waiver to operate at 400.1
MHz, since it's not a standard time and frequency signal-satellite service).
Anyway, sure is fun finding new (to me) signals and trying to figure out
what they are.

Andy

-----Original Message-----
From: David I. Emery [mailto:die at dieconsulting.com]
Sent: Monday, June 15, 2009 10:52 PM
To: Andrew Clegg
Cc: Scan-DC at mailman.qth.net
Subject: Re: [Scan-DC] More signals, this time ~400 MHz


On Mon, Jun 15, 2009 at 08:07:12PM -0400, Andrew Clegg wrote:
> 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".

	Interesting...


> 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!

	Radiosondes are usually sent up at 0000Z and 1200Z (eg 0 hours
UTC, or 8 PM EDT and 12 hours UTC or 8 AM EDT), and sometimes on the 6
hour mark (2 AM EDT and 2 PM EDT).

	Current ones transmit their GPS coordinates along with the
weather (temperature, pressure, humidity) data.  This allows measuring
winds aloft.   There are some software packages written in Europe that
will decode the signal and plot the position of the balloon and the
weather data (plus or minus calibration constants not available to the
program).

	A previous generation retransmitted Loran C signals on 100 KHz
for position determination...

--
  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."