Tuesday, August 17, 2010

Mystery beacon

For the last three hours or so I've been driven mad by an APRS beacon on 2m that I can't decode and which is not being gated to the internet by Richard MM1BHO's gateway. The amount of activity on VHF APRS round here is so low that I normally leave the receiver audio on so that I can hear whether anyone is about. The signal I'm hearing is quite solid, obviously from a fixed station or a stationary mobile, and though it isn't massively strong - just about making 1 bar on the Kenwood's signal strength meter - it sounds fully quieting and as good as other signals I hear which are decoded.

I tried both wide and narrow FM modes and when that didn't help I switched the antenna over to the FT-817 so I could try the AGWPE sound card decoder. I even tried plugging the antenna into the VX-8GR to see if that could decode it, but no joy. Listening to the sound of the beacon compared to the sound of my VX-8GR's beacon, the one I can't decode is quite a bit louder. I think it might be over-deviated.

So on the off-chance that someone trying APRS round here might read my blog, I thought I'd publish this posting. If it's you, try turning the audio into the transmitter down and you might get gated.


Lynn (D) said...

If you hook up the received audio to a PC's input and bring up AGWPEpro or some other program with a waterfall, or better yet, a sine wave display, what does it look like?

I've watched the sine wave display of PEpro and you can visibly see the clipping in the flat tops of the over-deviated signals rather than the nicely rounded sinusoidal curves of a non-clipped signal.

Lynn (D) - KJ4ERJ

Unknown said...

I looked at it on the waterfall and it looked as it sounded like 1200baud packet. I never thought to look at the oscilloscope display. Whatever it was, it has gone now, so it will probably remain forever a mystery.

Alex Hill said...

Not guilty m'lud. There isn't much VHF activity here full stop let alone APRS!

I have downloaded a copy of Aprsbb to try but I couldn't get the software to run.