27255 kHz 27.255 MHz FSK Data Link ΣSDR COMMSIGMA SDR KiwiSDR 1720 UTC 14 Dec 18

[R4002]

27255 kHz 27.255 MHz, 25 watts average or carrier power maximum TX under Part 95 of FCC rules.  There's a FSK data link signal readable on the ΣSDR KiwiSDR.  Not sure if this is the same network heard on the New York SDRs but it exhibits the same characteristics, with around 8 kHz of bandwidth. 

Listenable in FM or NFM mode but I generally tune into it in USB mode.  Some minor AM CB voice traffic QRM but when the frequency is clear you can see/hear the FSK signals buzzing away, albeit much weaker than other data networks on 27.255 MHz that I've heard. 

[Rob.]

Have you tried decoding the FSK? Curious if there is any readable data that might reveal its purpose.

[R4002]

I do not have the capability to do so.  Check out the Highland Falls, NY KiwiSDR and the Poughquag, NY KiwiSDR, both of those receivers have similar FSK data networks local to them on 27.255.  If you have the capability to decode the FSK I would be very interested to hear what data is being sent. 

The Highland Falls, NY KiwiSDR is close to an extremely active data link network on 27255, from what I can tell there’s at least 3-4 different transmitters (going by differences in signal strength) and one data burst every 1-2 seconds.

[R4002]

FSK data burst of various strengths coming in on the ΣSDR COMMSIGMA SDR KiwiSDR on the CT/MA border frequency 27255 kHz 27.255 MHz, bandwidth seems to be around 6 kHz.  One of them is local or semi-local (going by signal strength) but there are several other bursts that are just above the noise or marginally readable.  Going by the relative lack of activity on the other CB frequencies this early evening, I'd say these are distant (but not DX) transmitters that may or may not be part of the same system that the strong FSK signal is part of. 

The signals all have very similar characteristics and the transmitters almost seem to be answering each other.  The signals are very similar to the FSK signals logged previously on the various New York state SDRs.

[Josh]

I just tried the sigma sdr and got nada, if you can, please save a audio recording of the fsk, either iq or ssb or fm mode, and I'll see what the batputer says about the signal.

[ChrisSmolinski]

If you hang around the SDR for a few minutes you'll get some transmissions, I am seeing them now (1130z). There's several sites, as I get signals of varying strength all with the same characteristics.

No fun 27255 transmissions around here, it seems.

[R4002]

I just tried the sigma sdr and got nada, if you can, please save a audio recording of the fsk, either iq or ssb or fm mode, and I'll see what the batputer says about the signal.

If you hang around the SDR for a few minutes you'll get some transmissions, I am seeing them now (1130z). There's several sites, as I get signals of varying strength all with the same characteristics.

No fun 27255 transmissions around here, it seems.

With the COMMSIGMA  KiwiSDR you have to wait a little bit (sometimes several minutes or longer) for the local-sounding FSK signals.  Some of the networks seem to send signals randomly whereas others the transmissions are made on a regular basis.  The Highland Falls, NY KiwiSDR seems to have a local network of data transmitters on 27255 as well, and those are a lot more frequent, one every 2-3 seconds or so.  You can see on the waterfall that some of the transmitters are closer than others, and also note that there's center frequency variation of 100 Hz or so up or down from 27255.0 for different transmitters.

[Boriken]

I hear it in WNC when the band is open. Sounds like 4-5 different stations based on signal strength. Usually when the 28 MHz W2 & W3 beacons are coming in. Also have one on 26995 (1 sec burst every ~9 sec) that runs 24/7.

[Josh]

The times I listened in, most were off freq and one of them was badly distorted.

[R4002]

I hear it in WNC when the band is open. Sounds like 4-5 different stations based on signal strength. Usually when the 28 MHz W2 & W3 beacons are coming in. Also have one on 26995 (1 sec burst every ~9 sec) that runs 24/7.

Hearing similar signals on 26.995 makes sense too.  The data link/telemetry systems I've found use 26.995 MHz in their Canadian market spec versions (4 watt output instead of 10 watts).  Of course, if you're hearing something all the time on 26995, you're dealing with a local data link.  When the band is open check all six of the data/telemetry/RC frequencies for 26-27 MHz:  26.995 MHz, 27.045 MHz, 27.095 MHz, 27.145 MHz, 27.195 MHz and of course 27.255 MHz.  FCC rules permit 4 watts average power on 26.995-27.195 and 25 watts average power on 27.255 MHz, which explains why most systems use 27.255. 

The times I listened in, most were off freq and one of them was badly distorted.

Some of them seem to be several hundred Hz off center frequency of 27255.0 kHz.  The FCC rules stipulate a maximum bandwidth of 8 kHz with the center frequency of 27.255...I'd have to look up frequency stability requirements but I'm pretty sure these systems are violating those regulations as well.

[Strange Beacons]

This signal is very active today, as I just used the Highland Falls, New York KiwiSDR to tune the signal in, at 27252 kHz in USB mode. I also tried to decode it using Rivet 90 decoder in FSK (Raw) mode with the baud rate set at 200 and the shift at 1000 Hz. (That was the only setting that seemed to decode anything, though I'm not sure whether the results were accurate or not). Using Rivet at those settings, each data burst translated into what looks like long and short strings of binary numbers.

If anyone figures out the proper settings for Rivet, please let me know, as I'd like to try to decode.

[R4002]

This signal is very active today, as I just used the Highland Falls, New York KiwiSDR to tune the signal in, at 27252 kHz in USB mode. I also tried to decode it using Rivet 90 decoder in FSK (Raw) mode with the baud rate set at 200 and the shift at 1000 Hz. (That was the only setting that seemed to decode anything, though I'm not sure whether the results were accurate or not). Using Rivet at those settings, each data burst translated into what looks like long and short strings of binary numbers.

If anyone figures out the proper settings for Rivet, please let me know, as I'd like to try to decode.

The Highland Falls, NY one seems to be the most active data network on 27.255 that I've come across, although others have less frequent FSK activity.  The network near Highland Falls seems to have at least 4 or 5 different transmitters involved, going by the different signal strengths and how off-frequency the various signals are.