[MilCom] Monitor Project - What Fleet Broadcast Freqs Do You Hear?

[David I. Emery]

On Sat, Dec 16, 2006 at 10:01:35AM -0500, Mike Riffle wrote:
> Signal strength based on FM mode which sounds like noise. In SSB mode the
> data signal is clearly heard.

	FWIW, using a military surplus crossed yagi portable milsat beam
with a nominal gain of 12.5 dbi sitting on a flat roof about 24 feet
above the ground I read the signal strength of the 250.350 BPSK fleet
broadcast at 99 W at around -104 dbm on a calibrated spectrum analyzer
in 3 khz RBW..    The 250.550 signal is around -106 dbm.  This is from
a suburb of Boston, Mass.   I also see the 250.650 signal when it is up,
but don't have a level on it.

	Given the assumption that the surplus milsat antenna is still in
spec with respect to gain (probably not) this would imply around -115 to
-116 dbm as the actual signal level - which is a little less than I see
on a EMC testing broadband dipole oriented for maximum signal (maybe
-112 dbm on that with the 2.1 db dipole gain for around -114 dbm).

	And for those curious - the beam feeds a hunk of about 20 feet
of Andrew heliax 1/2 inch hard line and then a Avantek  GASFET LNA before
the spectrum analyzer, and the signal is at least 30-35 db out of the
noise on the screen.   If this group tolerated attachments I could include
a screen shot.   The signal, of course, is the classic sin(x)/x shape of
unfiltered BPSK.

	I have never had any trouble hearing the fleet broadcast 1200
baud BPSK (a raspy sound) with a regular whip antenna on my Yupi 7100 in
either nfm or USB/LSB mode.   The Yupi 7100 is quite sensitive...

	Some of us have demodulated and demultiplexed the 15 75 baud tdm
channels of the Fleet Broadcast over the years, but I know of no one who
has ever found any clear traffic in the streams - just unintelligible KG-84
encrypted traffic  and occasional crypto sync and start sequences or idle.  

-- 
   Dave Emery