[GPS_Standard] Fixed value offset for frequency

[Bert, VE2ZAZ]

Yeah, there had to be something wrong somewhere. It is a good thing that you found it that easily. Disappointing to hear that this input would be unterminated. With lots of reflections flowing back and forth, even the source may act up. No wonder.

Cheers,

Bert, VE2ZAZ
  ----- Original Message ----- 
  From: Stanley Reynolds 
  To: Bert, VE2ZAZ 
  Sent: Friday, February 13, 2009 9:04 PM
  Subject: Re: [GPS_Standard] Fixed value offset for frequency


  Bert,

  Checking the counter ( a Racal-Dana 1992 ) as you suggest it reads a stable 5,000,000,00 with either the GPSDO or Caesium standard. Also the Caesium reads very close to .30 usec or 5X10E-12 as measured with a Austron 2100f loran receiver. The GPSDO offset is much more at 100 to 200 usec measured with the loran. The difference between the two as measured with the counter is very stable over a 24 hour period just the GPSDO is a little low. I think I will look closer at the GPSDO power supplies and RF signals. The output looks clean on the scope with a 50 ohm terminator, but I have not looked at the pps and oscillator outputs before they get to the controller. What ever is in error is very stable and doesn't drift much as I can tell with my limited skill. I also have other GPSDOs but it is all unproven.

  As I was writing this I had the idea to place a tee and terminator at the counter external standard input it now reads as expected, problem solved :-) 

  Stanley N4IQT




------------------------------------------------------------------------------
  From: "Bert, VE2ZAZ" <ve2zaz at sympatico.ca>
  To: gps_standard at mailman.qth.net
  Sent: Friday, February 13, 2009 3:38:55 PM
  Subject: Re: [GPS_Standard] Fixed value offset for frequency

  Hi Stanley,

  Unfortunately it is not possible to add such a small offset to the FLL. 
  Changing the nominal value to 0x67FF will cause a one-Hertz offset, which is 
  way too much.

  Instead of trying to patch up your counter, I suggest you try finding what 
  is wrong.

  A good way to verify if your counter has a problem is to feed any 5MHz 
  signal, say your frequency standard, to both the RF input and the reference 
  input. The counter should normally alternate the dispaly between 4,999,999 
  and 5,000,000, or always 5,000,000 depending on the type of counter. If you 
  still read high, then there is a problem. Also check for power supply noise 
  on all rails of your counter.

  Assuming the counter is fine, what guarantee do you have that your Caesium 
  standard is within specs? Are you convinced that the GPSDO has achieved the 
  expected accuracy? What makes you think you can trust it? We are dealing 
  with "act of faith" devices here. We should always question something we 
  cannot demonstrate.

  Let us know the outcome!

  Bert, VE2ZAZ


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