KiwiSDR GPS frequency correction issues resolved - new advice if using an external GPSDO is to set to 66.66 MHz


Rob Robinett
 

In my next WD build I will employ kiwirecorder's  --resample  option to improve frequency accuracy and spectral purity of Kiw's which use the internal GPS services

On Mon, Sep 5, 2022 at 5:10 AM Glenn Elmore <n6gn@...> wrote:
Yes, that's probably optimum for frequency accuracy and plenty good with
Bodnar's for purity.  I'm not even certain that more digits would make
measurable degradation as a Kiwi clock.  The Bodnars use Si5328's which
have microwave VCOs rather than sub 1 GHz ones like the Si5351. This
gets one another 14 dB ( or something) suppression of spurious.  I had a
quick look last night at a Bodnar Mini and I don't think it really
matters much what you use so 66.660 MHz is a good choice if it buys zero
frequency error.

I had to use the 5351 instead of the 5328 in the Kiwi frequency extender
and the (subset) Reference board ( 'poor mans Bodnar') because of parts
availability and ~ 1 year times. Cost is quite different too.

On 9/5/22 07:43, WA2TP - Tom wrote:
> This seems to suggest that while using an external clk gpsdo like the
> bodnar, it should be set to 66.66. Currently I have mine set to 66.6666.







--
Rob Robinett
AI6VN
mobile: +1 650 218 8896


Glenn Elmore
 

Yes, that's probably optimum for frequency accuracy and plenty good with Bodnar's for purity.  I'm not even certain that more digits would make measurable degradation as a Kiwi clock.  The Bodnars use Si5328's which have microwave VCOs rather than sub 1 GHz ones like the Si5351. This gets one another 14 dB ( or something) suppression of spurious.  I had a quick look last night at a Bodnar Mini and I don't think it really matters much what you use so 66.660 MHz is a good choice if it buys zero frequency error.

I had to use the 5351 instead of the 5328 in the Kiwi frequency extender and the (subset) Reference board ( 'poor mans Bodnar') because of parts availability and ~ 1 year times. Cost is quite different too.

On 9/5/22 07:43, WA2TP - Tom wrote:
This seems to suggest that while using an external clk gpsdo like the bodnar, it should be set to 66.66. Currently I have mine set to 66.6666.


WA2TP - Tom
 

This seems to suggest that while using an external clk gpsdo like the bodnar, it should be set to 66.66. Currently I have mine set to 66.6666.

On Sep 5, 2022, at 4:34 AM, Gwyn Griffiths via groups.io <gxgriffiths@...> wrote:

John Seamons issued a fix in v1.557 for the absence of GPS frequency corrections when there were no browser connections.
The problem was outlined in post
https://groups.io/g/wsprdaemon/topic/kiwisdr_gps_frequency/93331251

That fixed has worked well. So well that it led to attributing the source of a "1 Hz offset" between some KiwiSDR users using GPSDOs set to 66.6 MHz and the now well-corrected Kiwis. The error is due to the fixed frequency relationship between the clock frequency and the 12 kHz audio sampling rate. 
John Seamons has provided a description at
https://forum.kiwisdr.com/index.php?p=/discussion/2721/external-clock-frequency-compensation-not-fully-applied#latest

Exact 12 kHz audio sampling rate is possible if the External clock frequency is set to 66.66 MHz. This is now suggested best practice.
KiwiSDRs using their own GPS frequency corrections after v1.557 update will be 0.1 Hz different at WSPR baseband frequencies because the internal clock is a nominal 66.6666 MHz.

Gwyn G3ZIL


Gwyn Griffiths
 

John Seamons issued a fix in v1.557 for the absence of GPS frequency corrections when there were no browser connections.
The problem was outlined in post
https://groups.io/g/wsprdaemon/topic/kiwisdr_gps_frequency/93331251

That fixed has worked well. So well that it led to attributing the source of a "1 Hz offset" between some KiwiSDR users using GPSDOs set to 66.6 MHz and the now well-corrected Kiwis. The error is due to the fixed frequency relationship between the clock frequency and the 12 kHz audio sampling rate. 
John Seamons has provided a description at
https://forum.kiwisdr.com/index.php?p=/discussion/2721/external-clock-frequency-compensation-not-fully-applied#latest

Exact 12 kHz audio sampling rate is possible if the External clock frequency is set to 66.66 MHz. This is now suggested best practice.
KiwiSDRs using their own GPS frequency corrections after v1.557 update will be 0.1 Hz different at WSPR baseband frequencies because the internal clock is a nominal 66.6666 MHz.

Gwyn G3ZIL