Sunday, March 03, 2013

Ghosts on JT9-1

I spent a couple of hours working JT9-1 on 20m this afternoon. I only messed up once when I forgot where I was in the sequence. I could do with the software showing the outgoing message in the log as well.

I think word of the new mode is spreading slowly as even on a Sunday there were not many new stations to work. N1ISA(FN41), WB2LMV(FN21) and KC2RDC(FN14) were the only DX worked.

One Italian station was a record +24dB during one call. I reduced power to 1 watt but I still received a +00 report from him. I don't know how much power he was using but it is a bit unfair to accuse a station of using too much power when even QRP signals are strong. WSJT-X seems to hold up better than JT65-HF in the presence of a very strong signal, as even in the presence of signals well above 0dB I was still getting decodes.


One thing I have noticed when receiving strong signals is that I get duplicate 'ghost' decodes at 100Hz intervals on either side of the main trace. Look at the four decodes of IK3SCB at 1701. There must be some 100Hz modulation of the signal, but I don't know if the cause is at my end or his.
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5 comments:

  1. Bert, PA1BSunday, March 03, 2013 9:46:00 pm

    Hello Julian, 24 dB is 250 times more power than 0 dB. Even reducing your own power further to show the concept of QRSS and low power, is NO guarantee for understanding. Hi.
    73, Bert

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  2. Paul Stam PAØKMonday, March 04, 2013 5:53:00 am

    I think that 5 watts is more then enough for JT9-1. 73 Paul

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  3. PatrickMonday, March 04, 2013 10:33:00 am

    Hi Julian,

    I have also noticed the same here...multiple decodes from the same station with 100 Hz intervals. Not only with JT9 but have seen this in JT65 as well. Is it too much power, or ALC, or is it just at our end the receiver having difficulties...who knows.

    73 Patrick ON4CDJ

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  4. UnknownMonday, March 04, 2013 10:55:00 am

    I have a theory. It is power supply hum modulation of the signal. 50Hz x 2 (full wave rectification). If so, USA stations should have ghosts at +/- 120 Hz. What do you think?

    Julian G4ILO

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  5. PatrickThursday, March 07, 2013 6:53:00 pm

    Hm that makes sense Julian.
    And most likely using a non-isolated soundcard interface, together with a bad PC power supply.

    Patrick ON4CDJ

    ReplyDelete