[hpsdr] New clock oscillator for OpenHPSDR?

[Phil Harman]

The close in phase noise of the 122.88MHz VCXO is reduced within the bandwidth of the loop filter due to the effects of the internal/external 10MHz reference. 

This is the reason why the close in phase noise specification is better than that of the master oscillator alone.

73 Phil...VK6PH 



From: Brian Lloyd 
Sent: Saturday, December 14, 2013 2:06 AM
To: Helmut, DC6NY 
Cc: hpsdr at lists.openhpsdr.org 
Subject: Re: [hpsdr] New clock oscillator for OpenHPSDR?

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On Fri, Dec 13, 2013 at 10:52 AM, Helmut, DC6NY <dc6ny at gmx.de> wrote:

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  Hi Kjell.

  Thanks for information, but I see no direct chance for any substitution in
  this 5V sine wave application. On the 10 MHz level phase noise hasn't been
  an issue and concerning to the sampling frequency 122,88 Mhz I'm not sure
  that the approx. 10 dB better phase noise can improve SFDR dramatically. But
  it's interesting that a lot of suppliers meanwhile  discover phase noise a
  determining factor of total system's performance.


Please correct me if I am wrong, but the loop filter at the output of the phase comparator prior to the control input at the 122.88MHz master oscillator effectively attenuates the phase noise from the 10MHz reference thus preventing it from affecting system performance. I would expect the native phase noise of the 122.88MHz master oscillator to dominate the phase noise performance of the system. This would mean that a low-phase-noise reference (GPSDO or Rb) is not that necessary.

Am I correct?

-- 

Brian Lloyd, WB6RQN/J79BPL      
706 Flightline Drive
Spring Branch, TX 78070
brian at lloyd.com
+1.916.877.5067


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