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.

3 comments:

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

Julian 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.