[hpsdr] Precise receive frequency measurement

[John Marvin]

The error in "actual RX" frequency can be up to ~29 millHertz on 
Mercury/Hermes. Not significant in most cases, but for FMT contests that 
is in the area of accuracy that top FMT'ers achieve. So I would think it 
would be important to know about the algorithm for two reasons: 1) to 
know the actual frequency so you can correct for it, or 2) to choose a 
VFO frequency that has minimum error, i.e. less than 1 or 2 milliHertz.

John
AC0ZG

On 3/8/2013 4:19 AM, Bruce Beford wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> Which is exactly what I do, Phil. Thanks. I asked "in the open", for those
> who may not know this. I have dabbled in the FMTs that are run regularly,
> and I have used the Mercury/Excalibur with the Trimble Thunderbolt GPSDO.
>
> In the past, I have been able to nail the mystery signal down as close as 9
> milliHertz on 20M. Down in that accuracy range, Doppler shift is the biggest
> issue, and causes the operator to use a fair amount of "Kentucky windage" to
> place the best guess. Knowing your actual RX freq setting to within a couple
> milliHertz does not really grant you any better accuracy in the over-the-air
> measurement, in my experience.
>
> 73,
> Bruce
> N1RX
>
> -----Original Message-----
> From: Phil Harman [mailto:phil at pharman.org]
> Sent: Friday, March 08, 2013 3:07 AM
> To: Bruce Beford; hpsdr at lists.openhpsdr.org
> Subject: Re: [hpsdr] Precise receive frequency measurement
>
> Yes,  but it will be if you use an external 10MHz reference that has your
> required accuracy.,
>
> 73 Phil...VK6APH
>
>
>
> -----Original Message-----
> From: Bruce Beford
> Sent: Friday, March 08, 2013 10:05 AM
> To: hpsdr at lists.openhpsdr.org
> Subject: Re: [hpsdr] Precise receive frequency measurement
>
> ***** High Performance Software Defined Radio Discussion List *****
>
> Thanks, Phil.
> Doesn't the overall accuracy of this formula assume that the 122.88 MHz
> clock -is- in fact, exactly correct?
>
> 73,
> Bruce, N1RX
>
>> 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
>
>
>
>
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