[time-nuts] Doppler and FMT

[quartz55]

I knew it was not that easy.  I didn't think about WWVB, and yes, I hear them quite often on 20.  So it's just a matter of averaging what you can measure and assuming that the average will be close?  I can imagine the shift can be all one way or the other for extended periods and how would anyone know which way?  I'll have to check another signal that I know is not a double and see what I see.  With SpecLab, it's easy to see mHz, but it's constantly changing so I guess one needs to log the data and use the spreadsheet to average it and hope it's close.  The other thing is the 2000 wanders around especially when the fan goes on, so I've got a circuit to lock the MO to a GPS.  XRef-VS, there are others for other radios too.  We'll see what happens when I get the XRef installed and working.

When I saw the WWV/B? signals I figured it was just how lucky you were.  If I'm seeing 2 Hz spread how can anything be measured with precision?  You can get close to anything once, it's doing it all the time that counts.

Dave
N3DT
  ----- Original Message ----- 
  From: Dan Rae 
  To: Discussion of precise time and frequency measurement 
  Sent: Thursday, September 19, 2013 10:07 AM
  Subject: Re: [time-nuts] Doppler and FMT


  On 9/19/2013 6:48 AM, quartz55 wrote:
  > I was playing with SpecLab and my TS-2000 just to see how accurately I could measure frequencies in the HF region.  I notice when I set the rx on cw and listen to the 750 Hz output of WWV at 15 or 20 MHz with SL, I get like 2 and sometimes more tracks about 2 Hz apart constantly shifting around. I assume this is Doppler going in and out?  If that's so, how can anyone reasonably expect to measure any ionospheric HF signal in the mHz range?
  >
  >
  Dave, it's not that easy.  I did the ARRL FMTs a few years back when 
  they were transmitting from the other side of the States and thought I 
  was doing well to get within 0.1 Hz.  The phase shifts on 7 and 14 MHz I 
  was seeing due to Doppler were up to 360 degrees, and quite rapid.

  Mind you I was using non computer techniques [1], so averaging by 
  eyeball was possible.

  Also if you are using WWV / WWVH, here at least, you often get both 
  signals at similar strength, so you might well be seeing two different 
  offsets.

  Dan

  ac6ao

  [1]  looking at the 100 kHz IF output of the receiver on a scope, both 
  scope trigger and Rx reference driven by homebrew GPS unit.
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