[hpsdr] Disabling 10 MHz clock on Penelope

[Phil Harman]

Hi Alberto,

Perhaps I can explain.  Both Mercury and Penelope have 122.88MHz master clocks.  These are used to derive the various signals needed by their respective FPGAs.

Since we generally want to transmit and receive on the same frequency we can't rely on both of these clocks being on exactly the same frequency. So we use a 10MHz reference that both these clocks are locked to.  The 10MHz can come from Mercury, Penelope or Atlas ( via Excalibur perhaps).

If you use a high accuracy external 10MHz reference - say a GPS locked reference, then your Tx and Rx frequencies also be very accurate.  We have reports of folks having an accuracy  of  2 mHz  ( 2 milli Hz!).

If you don't select any 10MHz reference then you may get lucky and find your two 122.88MHz master clocks are close enough not to be a problem.
So if you have a nice accurate clock and you remove your 10MHz reference then, as you found, you may only move a few Hz.

In my shack today it reached 34C - I can tell you my clock moved a lot more than 2Hz without a 10MHz reference connected!

73's Phil....VK6APH 
  ----- Original Message ----- 
  From: Alberto I2PHD 
  To: HPSDR list 
  Sent: Monday, December 21, 2009 7:42 PM
  Subject: Re: [hpsdr] Disabling 10 MHz clock on Penelope


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  I never understood how it can be possible that if you disable the Penelope 10 MHz clock and the Mercury 10 MHz clock,
  deselecting the relative bits in the USB stream inbound to the HPSDR, nevertheless reception continues, 
  albeit on a frequency a few Hz removed, but still with xtal stability...

  73  Alberto  I2PHD



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