[hpsdr] Penelope measurements

[Mark Amos]

Folks,

I did some more playing around with Penelope this weekend testing the frequency of the transmitted output.  
Penelope had been powered up for about a half an hour. These were tests run at 10.101000 MHz.

I found that when I selected Penelope for the 10 MHz clock source the transmit signal was low by 133 Hz 
(10.100867).  When I selected Atlas as the 10 MHz clock source (using an an external GPSDO fed to pin C16 on 
the Atlas bus) the measured transmit frequency was about 24Hz high at 10.100024.  

I expected it to be spot on. (A similar experiment with my SDR1000 showed the output to 10.101000 using the 
same GPSDO as with Penelope and same counter.)

I believe the measurements to be accurate - I'm using an HP 5328A counter with a GPSDO external clock that 
measures the GPSDO's to within 1 Hz at 10 MHz.  Also, when I zero beat the GPSDO driving Penelope against 10 
MHz WWV with the SDR1000 and Ten Tec Orion it seems to be dead on when it shows 10.000000 on the counter.

So, I think there's something wrong with my expectations.  Shouldn't the transmitted frequency be closer than 
2.4 PPM?

Just to be certain that my question is not misunderstood - I'm not complaining about this; I'm really just 
trying to learn something!

Thanks in advance!

Mark