I have just started playing with SDR so I downloaded the relevant amateur band plan for my location, the UK. Tuning around I found things like POCSAG/FLEX pagers as expected and amateur radio (e.g. FM repeaters) at frequencies matching the band plan.

However I also found some signals just above 145.8Mhz, which I noticed from the band plan is reserved in the UK:

145.806-146.000, 12 kHz, All Modes - Satellite exclusive

I am using an Ettus SDR and a Comet SMA703 antenna, which is designed for 144/400/1200Mhz. However, with this tiny antenna I was not expecting to receive anything from space, especially indoors.

An example of the signal is shown below:

enter image description here

There are a few more similar signals just a little higher up:

enter image description here

Some seem to be a fixed tone, some sound like they might be morse code when using the CW-U mode in gqrx.

I have been looking for around 30 minutes and none have shifted in frequency or disappeared. I had a look at a satellite list and used WXtrack to see what was overhead, but nothing seemed likely.

Can anybody tell me what these signals are likely to be?

  • $\begingroup$ I'm not sure about the UK, but its worth noting that in the US, the generally recognized bandplan is produced by ARRL and is nothing more than a gentleman's agreement... there is no force behind it. I suspect the RSGB bandplan has the same limitations, so even if a subband is marked "exclusive" it isn't guaranteed to be. $\endgroup$
    – KD8EVL
    Commented Jan 6, 2015 at 16:22
  • $\begingroup$ @KD8EVL That "gentleman's agreement" does have force behind it, if nothing else, then through §97.101(a): "In all respects not specifically covered by FCC Rules each amateur station must be operated in accordance with good engineering and good amateur practice." Following the band plan is "good amateur practice". Some jerk operating in the satellite band would make people who went through great trouble to launch a station into space a little angry, and I'm sure corrective action would be taken if necessary. $\endgroup$ Commented Jan 22, 2015 at 13:04

2 Answers 2


I'm guessing many those signals are just noise. A fixed tone carries no information, so there would be no reason for a satellite (or anything else) to transmit it intentionally.

The noise could be from an oscillator in some nearby electronics, or even from within the receiver itself. The noise may not even be at the frequency it appears in the waterfall: nonlinearities and intermodulation can make signals appear at frequencies where they actually are not. Sometimes you can identify these spurious signals by changing the LO frequency of your receiver and noticing how the signals move. For some, you may see them move by something other than the change in the LO. For example, if you tune the LO down by 100Hz, the signal may move by 300Hz.

  • 1
    $\begingroup$ @David : Ettus SDR isn't the quietest receiver either. Might be interesting to terminate the antenna input connection and then see what you get. $\endgroup$
    – rickhg12hs
    Commented Jan 5, 2015 at 5:27
  • $\begingroup$ With the antenna terminated I see a pair of signals at 144Mhz with the same spacing as my unusual signal, great idea! Maybe I am seeing lots of copies of this. Perhaps add another answer? $\endgroup$
    – David
    Commented Jan 5, 2015 at 21:58
  • $\begingroup$ If it's a harmonic, you will see it at other higher frequencies but with a lower signal strength. You can also track down the fundamental frequency of this unusual signal. $\endgroup$ Commented Jan 22, 2015 at 4:15

LED and CFL lights are a known nuisance to hams. It could possibly be one or some equally non-EMC conscious electronics.


  • $\begingroup$ With all the lights off I see nothing particular, but of course it could be a neighbour. I will try on a battery powered laptop to see if this makes a difference. $\endgroup$
    – David
    Commented Jan 5, 2015 at 21:59

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