[hpsdr] FMT differences between Magister and Metis?

[Phil Harman]

Hi Ron,

I can't think of any obvious way that Metis and Ozy/Magister can have an 
effect on the receive frequency.

Both send a 32 bit word to the CORDIC on Mercury.  If we were dropping some 
of the lower 32 bits when using Metis then I would have expected the 
frequency error to be 2^n based which it is not.  I guess we could be 
altering the bits in some manner but that would be odd this late in the 
development.

The rate that  Metis or Ozy/Magister sends data to the PC is determined by 
the 122.88MHz clock on Mercury since neither boards have any timing 
knowledge.

If you could please describe in a little more detail how you are measuring 
the frequency error then perhaps I can reproduce it here.

73 Phil...VK6APH


----- Original Message ----- 
From: "Ron Mozer" <ron at wy3d.org>
To: <hpsdr at openhpsdr.org>
Sent: Saturday, March 05, 2011 8:56 AM
Subject: [hpsdr] FMT differences between Magister and Metis?


> ***** High Performance Software Defined Radio Discussion List *****
>
> Very curious, using the PowerSDR v1.19.3.3 (W5WC 2/25/11) I did a little 
> experiment using K1JT's FMT (Frequency Measuring Test) utility.   My setup 
> includes an Excalibur feeding a 10 MHz reference to the Atlas buss from a 
> Thunderbolt GPS with a short term error in the realm of 0.03 PPB.
>
> By only changing the physical interface and matching it in the PowerSDR 
> setup, I see about 0.35 Hz difference in the measured frequency between 
> the USB interface on Magister and the IP interface on Metis when 
> referencing WWV on 10MHz.
>
> In fact Metis has a repeatable error of  about -0.35 Hz compared to a more 
> respectable error of less than 0.007 Hz when using Magister.
>
> If it makes a difference, I still have Metis V 1.0 installed and am 
> running on a Windows 7 x64 platform.
>
> Perhaps those playing with FMT can provide some insight as to tricks they 
> do with the HPSDR to minimize error.  I was thinking of trying to use 
> ghpsdr3 running multiple receivers.  Have a couple receivers locked to 
> different WWV frequencies and one measuring the unknown frequency.  This 
> might allow one to zero out apparent frequency changes due to the Doppler 
> effect.
>
> 73 de WY3D
> Ron
>
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