[Elecraft] Frequency reference for the K3 directly off a GPS

[Sverre Holm (LA3ZA)]

I have done some more experimenting now with my poor man's 10 MHz reference.
The ublox Neo-7 GPS is a lousy frequency reference in most respects, except
that it is accurate in keeping exactly 10 million periods per second. My
experience is that the K3 has enough internal averaging to deal with that.

Using a ublox Neo-7 (USD 12 on Ebay) and a 74HC04 as a driver to feed the 10
MHz to the 50 ohm input of the K3EXREF the K3 accepts the input and I see
the star in REF*CAL blinking. 

The reference frequency now starts at 49,379,680 and stabilizes to
49,279,650 after some 15-20 minutes. My initial setting for the reference
was 49,379,640 which I determined manually when the K3 was new in 2009 or
so.

I am going to write this up on my blog with schematics eventually.



Sverre Holm (LA3ZA) wrote
> Some recent GPS modules (ublox Neo 7) have a programmable output that in
> addition to the 1 pps output can be programmed even to output 10 MHz. This
> output has a lot of jitter as it seems to be derived from a 48 MHz clock
> which is divided down in such a way as to generate a mix of short and long
> cycles but so that the average frequency is maintained accurately at 10
> MHz.
> 
> A description can be found here 
> https://sites.google.com/site/g4zfqradio/u-blox_neo-6-7 and performance is
> partly described here:
> https://www.febo.com/pipermail/time-nuts/2014-August/086257.html
> 
> My question is regarding the K3 external reference input. Is this source
> good enough to drive the K3 reference? Can the K3 clean up the jitter
> internally, or does the K3 require a source with much less phase noise?





-----
Sverre, LA3ZA

K2 #2198, K3 #3391,
LA3ZA Blog: http://la3za.blogspot.com,
LA3ZA Unofficial Guide to K2 modifications: http://la3za.blogspot.com/p/la3za-unofficial-guide-to-elecraft-k2.html
--
View this message in context: http://elecraft.365791.n2.nabble.com/Frequency-reference-for-the-K3-directly-off-a-GPS-tp7606275p7607984.html
Sent from the Elecraft mailing list archive at Nabble.com.