[hpsdr] Precise receive frequency measurement

[Phil Harman]

Hi Brian,

The frequency is sent to Hermes/Mercury as a 32 bit value in Hz.  This is converted to a 32 bit phase word as follows:

phase =  frequency * 2^32 / 122880000

You will be able to calculate the actual frequency from the above. 

73 Phil...VK6APH 





From: Brian Lloyd 
Sent: Friday, March 08, 2013 12:03 AM
To: John Marvin 
Cc: hpsdr at lists.openhpsdr.org 
Subject: Re: [hpsdr] Precise receive frequency measurement

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On Thu, Mar 7, 2013 at 2:28 AM, John Marvin <jm-hpsdr at themarvins.org> wrote:

  ***** High Performance Software Defined Radio Discussion List *****

  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).


Ditto this request. I plan to use my Hermes board in the frequency measurement tests and knowing the truncation and/or round-off errors would be really useful since I am shooting for something close to 1e-10 accuracy. 

-- 
Brian Lloyd, WB6RQN/J79BPL
3191 Western Dr.
Cameron Park, CA 95682
brian at lloyd.com
+1.767.617.1365 (Dominica)
+1.916.877.5067 (USA)



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