[hpsdr] Precise receive frequency measurement

[John Marvin]

Hi,

Someone previously mentioned (I think it was Joe) that Hermes/Mercury 
does not always use the exact frequency that is programmed into the 
receiver, due to the down conversion / decimation algorithms used in the 
FPGA. Is there any documentation on this? For example is there a formula 
for determining which frequencies will be exact? If not, will 
frequencies that are exact multiples of the sampling rate be exact (for 
example 7.056 Mhz in the 40m band is an exact multiple of 48 Khz, 
assuming 48 Khz was being used for the sample rate).

Any information would be appreciated,

John
AC0ZG