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3329Re: [wsjtgroup] Sked and rx frequency - help and clarification

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  • Lee Scott - AA1YN
    Nov 13, 2006
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      At 08:58 AM 11/13/2006 +0000, Enrico - IZ0GYP wrote:
      >Hi all,
      >I'm a novice for EME (QRP with 9 element and 200W) and i'm still
      >studying the JT65B to be more familiar with the communication
      >procedures, trying to avoid mistakes and loose of time to the stations
      >that would reply to my skeds.
      >Up to now i succesfully completed 3 QSOs.
      >Anyhow my problem is the following.
      >If someone, on the EME chat, state a CQ call on 137 (144.137) this
      >means that both the calling station and the station that would like to
      >reply to his call shall have the VFO on 137,0 during TX.
      >Now, i'm using a FT-736R and i'm almost sure about correctness of the
      >freq calibration.
      >Usually a receive CQ station EME calls at SpecJT center when my VFO is
      >approx. 0,7 KHz higher (144.137,7).
      >Otherwise, leaving the VFO at 137,0 , i will see caller EME signals at
      >the far right side of the SpecJT screen (or even outside).
      >That's of course due to the Doppler effect but my concern is if 0,7
      >KHz is a standard frequency doppler shift on VHF or is a little bit
      >too big?
      >Due to my QRP conditions i can't receive my own echoes and the other
      >stations will see only light signals on their PCs.
      >I would like also to be sure at least that i'm not spending time
      >calling on a wrong frequency where the CQ caller station would never
      >receive me.
      >Shall i therefore use the second FT-736 VFO on 0,7 KHz higher during
      >rx (FT-736R does not have independent RIT function)?
      >Is my understanding correct that if i will be transmitting on the sked
      >frequency also my EME signals will be "falling" in the center part of
      >SpecJT screen of the other station (i guess that he will be also
      >listening 0,7 KHz higher)?
      >Sorry if the questions may be appear probably confused (or even
      >terrible) to you but your help will be very appreciated on my side.
      >Thanks for your kind reply and understandings
      >Best 73's de Enrico - IZ0GYP

      Hi Enrico,

      You are in the same situation I was in two years ago. Put his signal in the
      center of SpecJT's window. I don't know how you determined your FT-736
      frequency's accuracy but I would bet you are at least 500 Hz off. I don't
      know what the Moon's Doppler effect was at the time you were trying to
      contact someone but IF the Doppler was +200Hz and your station was +500Hz
      off, that would account for +700Hz. Doppler effect depends on the location
      of you and the other station. If your echo would have a Doppler of +200Hz
      and the other stations echo had a Doppler of -200Hz, then the QSO Doppler
      would be 0Hz. If this was the case, then your rig's frequency offset would
      have been +700Hz off. So it is hard to tell without knowing the circumstances.

      If you signal is getting through, the other station will locate you. JT65
      is in many ways like PSK31 but then again better. JT65 has the capability
      of searching over a +/- 400Hz range for your sync signal. Do not try to
      compensate for the Moon's Doppler effect. Just set your frequency so that
      their signal is in the center of SpecJT and let the other station find your
      signal. When the other station sees your sync signal, they will generally
      freeze their receive frequency on it and provide them with a better decode.
      Even if they don't, JT65 will search the tolerance range for a sync signal
      down to the noise level and attempt to decode it. The best operation you
      can do is make sure your PC time clock is matched with a time standard.

      The second best thing you can do is make sure your rig does not drift in
      frequency when transmitting. If Yaseu has a high stability option for the
      736, then get it. My Icom 746 has a bad drift and I had to build an oven
      for the crystal to fix it. I know that 2 stations both running barefoot
      IC-746 have a very hard time working each other even with AFC checked.

      I hope my answers help - if not ask away.

      73's and hope to catch you on the Moon.

      Lee Scott - AA1YN http://www.aa1yn.com
      Home of the VHF & Up Register http://www.aa1yn.com/vhf
      Home of the VHF Talk chatroom http://vhftalk.aa1yn.com
      Hooksett, NH
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