[hpsdr] High Accuracy Timing for HPSDR

[Rick Hambly (W2GPS)]

Neil,

 

Locking to 10K PPS does not provide all the benefits you would expect
because of the statistics of the 10K PPS signal.  That fact killed a "black
project" that Tom and I worked on a while ago. Locking to 1PPS is not more
difficult than locking to the 10K PPS and the Jupiter is an old design.
There are new receivers on the horizon that will all be 1PPS. 

 

Yes, the best locking solutions (including mine) are proprietary, but we may
be able to get past that with some thought or policy flexibility. We should
decide what oscillator (and clock) characteristics are important and design
to meet them. I have some ideas that I will share later.

 

Rick

W2GPS

AMSAT LM2232

 

  _____  

From: hpsdr-bounces at hpsdr.org [mailto:hpsdr-bounces at hpsdr.org] On Behalf Of
neil whiting
Sent: Thursday, May 25, 2006 6:18 AM
To: hpsdr at hpsdr.org
Subject: [hpsdr] High Accuracy Timing for HPSDR

 

A few thoughts on SDR frequency references. I'm not sure the Gibralter PCB 
needs to be as complex as suggested. 

- Most people who are worried about having GPS-accurate frequency are likely

  to have an existing reference source. 

- Many of those who don't have an existing reference are likely to be happy 
  with a simple OCXO tweaked to the right frequency. Locking to GPS is not 
  necessary for SDR operation. 

- If a locked frequency is required (eg for modern digital modes, 
  microwave EME, etc) 
  - locking to 1pps is tricky/complex and existing solutions may not be 
    open source 
  - locking to 10kHz as output by some GPS modules (eg. the Jupiter-T, 
    which is available surplus) is rather easier, just using a simple PLL 

It would seem that a good balance would be to provide 3 options: 
- an external reference input, 
- an option to use the Gibraltar PCB populated with just an OXCO, no locking

- use Gibraltar with simple PLL locking to 10kHz from a suitable onboard GPS

  module 

Does this make sense? Have I missed something? 
Are suitable GPS modules available at a reasonable price (new, not surplus)?


73, Neil G4BRK 

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