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10506Re: JT9-1 no decode on very strong signal why?

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  • booz2m
    Jun 14, 2013
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      Hello Philip

      It is hard for me to tell the exact reason why but I will give it a go anyway it if is not pure overloading or a timing issue.

      You and Michel, F1ABL, are about 1300 km apart and with several major airports in between (BHX, LGW, LHR, CDG and ORY) thus with lots of aircraft scatter possibilities. This may have caused a lot of multi path on top of the direct signal.

      It could also have been other phenomenons that caused the tight tone spacing in JT9-1, <2 Hz, to challenge the decoder when perhaps the multi path made the tones jump 10 Hz or more.

      I had a chat with Jim, VE1JF, the other week on the ON4KST 50/70 MHz chat. Jim is fairly active on 6 m with JT9-1. He said that he often experience signals to be visible in the waterfall yet they fail to decode. I suggested him to try JT4 or JT65 that both have "much" wider tone spacing then JT9. On the VUSHF bands path irregularities often distort the signal one way or the other. I believe that this is what you are experiencing. JT9 with its narrow tone spacing is not very robust to VUSHF paths. I acknowledge the challenge of till trying to see if JT9 will work given the circumstances. This is what ham radio is all about. Just like trying to land a marlin with an ultra thin fishing line.

      If you want to dig more into path issues you can try to listen for OZ7IGY. It transmit a mixed mode signal in a one minute cycle (PI4, CW and carrier). See more here: http://rudius.net/oz7igy The PI4 modulation is a cousin of JT4, JT9 and WSPR and like JT4F/G it has a wide tone spacing of about 234 Hz.

      Bo, OZ2M
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