[time-nuts] Comparing the frequency of two gpsdo's.

John Ackermann N8UR jra at febo.com
Sat Nov 13 20:44:41 UTC 2010


Bert, I just approved your message, so it should show up soon.  The reason for the size increase is that the internet email format is 7-bit ASCII, so a binary file has to be encoded down from 8 bits and grows as a result.

John

On Nov 13, 2010, at 3:32 PM, EWKehren at aol.com wrote:

> Hi
> I give up a 113.3 K picture attachment no text turns into 157 K. I tried.  
> It is particular frustrating when seeing how much bandwidth is wasted with  
> garbage that has nothing to do with time and frequency.
> Bert Kehren
> 
> 
> In a message dated 11/13/2010 2:14:04 P.M. Eastern Standard Time,  
> lists at rtty.us writes:
> 
> Hi
> 
> Ok, so right now you are looking at about 10 degrees out  of 360 where one 
> cycle is 100 ns. More or less you are in the 3 ns range.  
> 
> Some cheap stuff that will do better:
> 
> HP 5334
> HP 5335
> HP  5345
> HP 5370
> HP 5371
> 
> All are in the "sub $300" range on the  normal sites. Some are sub $100. 
> All are available with GPIB for  logging.
> 
> For a bit more money
> 
> HP 53131
> SR 620
> 
> You may  find one for sub $1000. Often you see them listed for nutty 
> prices. I  certainly would not pay anywhere near $1,000 for either one. 
> 
> The one  I'd go for is the 5334. It's smaller than the rest. They likely 
> are the  cheapest of the group. The ones I have *seem* to be more reliable 
> than some of  the rest of the stuff listed. 
> 
> All of them can run in any one of three  modes:
> 
> 1) PPS to PPS timing
> 2) PPS to 10 MHz edge timing
> 3) 10  MHz to 10 MHz timing
> 
> Number 2 on the list seems to have the fewest  issues. 
> 
> A completely different approach:
> 
> Pump both signals into  a phase detector (RPD-1 or X-OR or what ever) and 
> use a DVM to log the  voltage. You can get some super  overkill DVM's for 
> less than you can get  any of the counters. They will easily get you into the 
> sub ns range on  resolution. Weather the setup will be accurate at this or 
> that  level is  in the "that depends" category.
> 
> Bob
> 
> 
> On Nov 13, 2010, at  11:18 AM, Mark Spencer wrote:
> 
>> Hello:
>> 
>> I'm looking  for some advice about ways I can compare the frequency of 
> two gpsdo's.   To date I have been using an oscilloscope that supports phase 
> measurements to  measure the small (typically 10 degreees or so at 10 mhz) 
> change in phase  between the two signals over a period of a few hours and then 
> calculating the  frequency change.
>> 
>> I realize this is sub optimal but I wanted  to use the gear on hand.   
> Recently the phase measurement fuction of  my scope has stopped working.  
>> 
>> As the useage I have  ever found for the phase measurement function in my 
> scope was comparing the  frequencies between gpsdo's I'm thinking it might 
> be better to invest in some  other equipment rather then getting the scope 
> fixed.
>> 
>> Any  thoughts as to what could be obtained used for less than 1K that 
> would be  suited for this type of measurement ?
>> 
>> Regards
>> 
>> Mark S
>> 
>> 
>> 
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