[hpsdr] phase coherent timing (clocking)

[John Petrich]

Phil,

Thank you for your detailed and probably more correct understanding of the
timing arrangements than mine.  I understand the purpose of the strict and
stable phase coherence that Joe is most interested in for multiple Mercury
receivers.  

Maybe I was a bit out of pocket with my comments.  That said, I have
experimented at trying to have the TX and 'apparent' RX frequencies
simultaneously match up in my transceiver measured by my test gear.  I had
always detected a variable and small differences between the TX and RX, a
few Hz at most, and just felt I wasn't 'there' yet.  At the point when I
reduced the clock count to the single 122.88MHz and the single 10MHz
external clock with the phase coherent timing arrangement  I outlined, all
the measured frequency parameters came into alignment.  Random measurements,
wishful thinking, phase of the moon, bonkers American, I don't know.  Maybe
not phase coherency by itself, but simplifying the clock count seems to have
made a difference that I have observed in my situation.

I know that you will think about what I have observed and will likely have
further thoughts.  Please don't hesitate to correct me, shed light on, or
call into question what I think that I have observed.

Regards,
John, W7FU

-----Original Message-----
From: Phil Harman [mailto:phil at pharman.org] 
Sent: Tuesday, December 20, 2011 6:04 PM
To: John Petrich
Cc: hpsdr at lists.openhpsdr.org
Subject: Re: [hpsdr] phase coherent timing (clocking)

> What is accomplished with this modification?  For the first time ever 
> with my HPSDR transceiver, TX and RX, are on the exact same frequency.  
> Makes me feel good all over.
>

Hi John,

This modification should not be necessary in order to transceive on the same
frequency.

Both Mercury and Penny(Lane) are fitted with 10MHz TCXO's, either of which
can be sent to the Atlas bus so that the 122.88MHz clocks on each board can
both be phase locked to one or the other reference.

Alternatively you can use an Excalibur frequency reference on the Atlas bus
and use either its local 10MHz reference or an external source.

The selection of the relevant reference can be made using PowerSDR, KK etc.

Any of the above methods will ensure you Tx and Rx on the same frequency.
Joe's modification ensures you have phase coherence between multiple boards
which is required for diversity reception etc.

73 Phil...VK6APH




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