[hpsdr] High Accuracy Timing for HPSDR

[Robert McGwier]

The typical 10K outputs are locked to the 1pps which has large 
excursions of error due to sawtooth error large deviations. BUT, large 
depends on who you are and what your applications might be. Most people 
here are not trying to go for separated clocks to agree within 2 ns! For 
most, the accuracy derived from using the 10K pps output from a motorola 
receiver (or other source) is more than accurate and stable enough for 
our purposes here. I would prefer to use a source with no excursions if 
I were going to lock an LO to use in a 47 GHz transverter, well then I 
might care about these excursions. The 10 K pps signal, driving a 
Gibraltar based reflock will be better than most TCXO's in HF 
transceivers today and by a lot.

Bob



Rick Hambly (W2GPS) wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
>   
>
> ------------------------------------------------------------------------
>
> 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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-- 
AMSAT VP Engineering. Member: ARRL, AMSAT-DL, TAPR, Packrats,
NJQRP/AMQRP, QRP ARCI, QCWA, FRC. ARRL SDR Wrk Grp Chairman
Laziness is the number one inspiration for ingenuity.  Guilty as charged!


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