[time-nuts] Commercial solution - 122.88 Mhz low noise source

[Jeff Blaine]

I've got a couple of Red Pitaya 122-16 SDR and want to discipline them 
to an external low noise GPSDO source.  Wanted to see if there were some 
easy solutions that fell into this category.

For the prior generation (QS1R), I had built a homebrew OCXO based on a 
custom low noise crystal from ICM and that worked great for the 125 Mhz 
application.  Unfortunately this Pitaya is a bit removed in Fc and ICM 
has been out of biz for several years now.

The RP's on-board oscillator is the respectable Abracon ABLNO 122.88 
which runs about -115 dBc/hz at 100 Hz spacing and that's probably not a 
limitation for the unit.  Unfortunately the OSC is a bit too sensitive 
to external temp and wanders around quite a lot (+/- 5 PPM) compared to 
the homebrew OCXO - over the annual ambient temp range of (10-35C) (all 
datasheet referenced values). The Abracon unit is mounted on the board 
with the FPGA and sees additional temp range depending on other heat 
generation factors (FPGA loading).

I have a couple of commercial GPSDO on the bench now, so a pretty clean 
10 Mhz GPSDO reference is available now.  And I've seen enough board 
discussion to know that a homebrew GPSDO solution is one of those "it's 
harder than it looks" things.  Hence the desire just to buy whatever is 
the silver bullet, as long as it does not require too much silver.  ha ha

Appreciate any suggestions.  TKs!

73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com