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3330Re: [wsjtgroup] Sked and rx frequency - help and clarification

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  • Paul Whatton
    Nov 13, 2006
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      Hi Enrico

      Congratulations on your QRP EME. I'm also using a small station which is
      very similar to yours, a FT736R, 400 watts and a single 9 element F9FT.
      The FT736R is very stable and works really well on WSJT. The FT-736R is
      much stabler than my second rig, an Icom 746.

      It sounds from what you sayt that your 736 calibration is 700Hz out.
      Mine is about 200Hz out, so I know when my display reads say, 144.130.2
      I am actually on 144.130. So just take your 700Hz error into account. Or
      even better if you have the workshop facilities you could re-calibrate
      your display.

      Having done that you know what frequency you are tuned to, but what
      about the doppler? On 2m it is only a maximum value of about 300Hz and
      most of the time much less than that if like me you use elevation. But
      it is nice to be close to the correct frequency and the doppler can be
      tricky to get your head around. Having said that, if there is a pileup,
      it's often better to call a bit off frequency!

      I don't pretend to be an expert and maybe someone will correct me if I'm
      wrong here. But this is what I figured out.

      If you have a sked then yes you are right, transmit on what you know to
      be the correct frequency and stay there. Then look for your sked partner
      to be shifted by his doppler. You won't need the RIT, his traces will
      just be offset away from the centre frequency in WSJT by the amount of
      his doppler plus/minus any error in his transmit frequency. That's fine.

      BTW. I've noticed that even some big guns are not always exactly on the
      frequency they say they will be :-) If (when) you find your sked partner
      is a long, long way off frequency then you have a dilemma. Should you
      stay where you are or should you move?

      But how about when you want to answer a CQ?

      Even with just a single 9 element the majority of QSOs I make are by
      calling someone. Either by tail ending or by answering their CQ call.
      Most are random, I usually don't tell them in N0UK or ON4KST that I'm
      going to call.

      Here's what I do. Let's say I hear a station calling CQ and when WSJT
      decodes him it indicates I am receiving him with a DF of +300Hz. But
      entering his locator tells me his doppler is actually say, -120Hz. So I
      retune the receiver to a frequency 420Hz higher. I should now get a DF
      of -120HZ on his decoded signal, the same figure as his predicted
      doppler shift. I then call him on that frequency. If I have it figured
      out correctly this will make my transmit frequency the same as his, and
      my received signal will be close to where he hears his own echos (all
      the stations I work will be able to hear their own echos).

      As an alternative, if you really want to use the RIT you can dial in the
      amount of the doppler and then aim to receive the other station with a
      DF of 0.

      I didn't have much time in the EME contest yesterday before I had to go
      out. But I called CQ and two stations called me who were both
      "off-channel" by about 100Hz more than I would have expected from their
      doppler. So don't worry about it too much, even the big EMEers are not
      always spot on frequency.

      73 Paul G4DCV

      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
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