UHF SatCom round up

[AlanC]

Here's a round-up of what was audible over the past hour or so from Sheffield, UK. My RX setup is RTL-SDR dongle on a Raspberry Pi running as a RTL-TCP server, then SDR Sharp running on a Win 7 laptop. Antenna is a home brew 3-element yagi cut for 250MHz bearing 220 degrees azimuth and 30 degrees elevation. This is quite a potent set up- the pirates are mostly fully quieting signals. NB that the transponder bandwidths given are approximate.

Transponder outputs are easily seen by the lift in the noise by up to about 10-15dB over the receiver noise floor.

I am amazed how much pirate activity there is.


243.8 - 243.85 looks like 'Raindrops' some kind of frequency hopping system

244.075 8 transponders with about 4 kHz bandwidth. No visible activity.
244.085
244.095
244.105
244.115
244.125
244.135
244.145

244.185-   5 transponders with 3.5kHz bandwidth.
244.190
244.195
244.200 has narrow band data bursts, 2.5 sec every 7 sec
244.205 missing
244.210

245.200 25khz wide transponder, with FM voice pirates active

249.105 13 transponders of 4kHz bandwidth, many with data bursts
249.115
249.125
249.135
249.145
249.155
249.165
249.175
249.185
249.195
249.205
249.215
249.225

249.450 25khz wide transponder, with FM voice pirates active
249.575 25kHz wide transponder, 'sloping top'. wideband data bursts
251.325 25khz wide trasnponder, 'dome top'
251.700 25khz wide trasnponder, 'dome top'
251.950 25kHz wide transponder, flat top. wide band data bursts
252.050 25kHz wide transponder. FM Voice pirates active near the HF edge, narrow band data bursts near the LF edge.
252.150 25kHz wide transponder.
253.750 25khz wide transponder, with FM voice pirates active
253.850 25kHz wide transponder.
253.900 25kHz wide transponder with some very interesting signals;
1. at the LF end, beginning at 253.886180 are 11 tones on 170Hz spacing sounding very like the old VFT; no TTY visible though
2. Centered on 253.913.0, some odd signals that could be data of some sort or could be analogue speech encryption, listen on SSB mode...
3. In the centre, is en-clair US OM voice in AM mode sounding like Air Traffic Control (mention flight levels etc). Yesterday was much more active with almost continuous transmissions. Weak signal and due to QRM just to the HF side of the carrier I needed to use LSB to hear it best. 10.51 UTC Now Telling A/C to contact New York on [just unreadable] frequency

254.155 25kHz wide transponder. wide and narrow band data bursts in the centre, narrow band data signals near HF and LF edges.
255.450 25kHz wide transponder. FM Voice pirates active at both .440 and.460 - first time I've seen 2 pirate QSO's on same transponder!
255.550 25kHz wide transponder. with FM voice pirates active as always!
257.050 25kHz wide transponder with wideband data bursts and with FM voice pirates active near HF edge
257.150 25kHz wide transponder with wideband data bursts
257.500 30kHz wide transponder
258.550 30khz wide transponder
258.650 25kHz wide transponder
260.425 25kHz wide transponder with wideband data bursts and with FM voice pirates active a little LF of centre
260.525 25kHz wide transponder with wideband data bursts and with FM voice pirates ?Japanese? active a little HF of centre
261.280 25kHz wide transponder with data and what sounds like QRM on the input from wideband FM music station chopping in and out

261.875 25kHz wide transponder with wideband data bursts
262.075 30kHz wide transponder
262.100 5kHz wide transponder
262.150 5kHz wide transponder
262.175 30kHz wide transponder
262.200 5kHz wide transponder
262.275 30kHz wide transponder
262.375 30kHz wide transponder
263.725 30kHz wide transponder with wideband data bursts
265.350 25kHz wide transponder
265.450 25kHz wide transponder with wideband data bursts and with FM voice pirates active

Cheers
Alan

[Josh]

Well done. What bird/birds is this?

[WA4FHY]

Josh,
Probably the LAN (Atlantic) constellation, I doubt he would be able to hear the CONUS  constellation.
BTW: Matt Blaze put on a very interesting presentation, and later a demo, of TACSAT reception at
the WSWLfest last weekend. You can see the gist of his presentation at:

http://www.crypto.com/misc/uhf-sats/

I can just hear the SA pirates here with my RTL-SDR dongle (or the ICR-7000) connected to my discone
but they are too weak to really *hear* them. Now, if I could just find a Trivec 2055 TACSAT antenna
at a reasonable price... However, a homebrew yagi, as Alan uses, might be worth a try.
Paul

[ChrisSmolinski]

I had excellent results with this helical antenna I built several years ago (it has since been destroyed by a winter storm): http://www.radiohobbyist.org/blog/?p=933

[Josh]

Thanks for the info guys, here's a sat antenna build that may be of interest;
 MT magazine UHF Satcom antenna project
https://forums.radioreference.com/satcom-space-satellite-monitoring-forum/181378-mt-magazine-uhf-satcom-antenna-project.html

[autovon]

Thanks for the excellent wrap up!

[WA4FHY]

Chris and Josh,
Thanks for the antenna ideas. I will probably work on a homebrew
antenna of some kind but it will be a lower priority since there does
not appear to be much to be heard there - I don't speak Portuguese.

However that is an area of the spectrum, between VHF-FM and the
70cm ham band, that I'm not very familiar with, so I do want to explore
it some.
73, Paul

[Tim Bucknall]

the US ATC on 253.900 is currently in the clear here in Northern England if it helps if it helps

[R4002]

Chances are you're hearing ATC on 253.900 MHz AM mode mixing in with the SATCOM traffic on the same frequency.  My understanding was that UHF SATCOM systems didn't use AM voice but there's always the exception to the rule.  The transponders are wide enough in bandwidth that data/voice could be carried above and below the center frequency on 253.9 and the aircraft using that frequency would never know there was SATCOM traffic right above and below them in frequency.

[Tim Bucknall]

there is likely more than one ATC being relayed, from the time zone being used the strongest one heard here is from the west coast of North America.

253.9+ 41 = 294.9

Anyone got a north American UHF listing for 294.9?

[R4002]

Cursory Googling comes back with "Calgary, Alberta" but something tells me that's not it.  I searched on AirNav and wasn't able to find it via frequency search for 294.9 MHz or 294.900 MHz.  Could be a UHF simulcast of a VHF primary ATC frequency. 

Are you able to get any more identifying information about the ATC traffic you're hearing, Tim Bucknall? 

[Tim Bucknall]

i'll have another listed but its weak and difficult

simulcast seems like the best possible solution