[hpsdr] external 10MHz reference input
meijer.ha at home.nl
Sat May 18 10:26:25 PDT 2013
Thanks for sharing your experience concerning the freq jumping of the
internal 10MHz tcxo.
I have done some research for the 10MHz tcxo (FOX924b) that is used and
have come to the conclusion
that is a low-cost one, with not very high
So first thing I will try is to replace it with an other one, I think
maybe the CFPT-9301 ( http://www.farnell.com/datasheets/43326.pdf )
It has better temp stability then the FOX924b and the fase noise spec's
in it's data sheet.
> Hi Helmut,
> Yes I know this 'buffer' does clamp the ref. input between 0 and
> +/- 3.5V.
> I did try to change R142 to 120Ohm, then I get a kind of
> symmetrical 10Mhz square wave @+/-2tt, out of my sinus wave 10MHz.
> But unfortunately that did not cure the jumping in freq, with the
> external 10Mhz standard.
> Yes that 10Mhz standard is stable and does not show me that jumping.
> I almost start to believe there is a FGPA firmware problem some
> how not looking correct to the 10MHz reference all of the time.......
> I spent a month or so on this problem with Apache Labs and with Phil a
> couple of months ago. Phil spent a LOT of time trying to figure it
> out. Like you I proposed that there might be a problem with the DPLL
> as coded into the FPGA but after extensive review and testing, Phil
> determined the DPLL is working properly. He finally determined that
> the problem is *definitely* the 10MHz internal reference. It is quite
> easy to hear the frequency jumps if you listen to a high-order
> harmonic of the reference oscillator. The problem does not appear when
> the 122.8MHz clock is free running. It appears that the problem has to
> do with the digital temperature correction of the reference
> oscillator. It stays well within its specifications even with the
> frequency jumps, but the step function used for temperature correction
> is *REALLY* annoying. The whole process got Apache Labs looking for a
> better 10MHz oscillator that uses analog temperature compensation.
> Abhi told me that my 100D was being shipped to me with a different
> 10MHz reference and my preliminary tests have shown that the frequency
> steps are gone on the 100D. I don't know but I presume that they are
> using this new reference on new production radios.
> As for the problems with the external reference input, I experienced
> those as well too. Changing R141 solved the problem. I am now using my
> LPRO-101 Rb reference without difficulty or problem. Because of the
> frequency jumping I now use the Rb reference 100% of the time with my
> Brian Lloyd, WB6RQN/J79BPL
> 706 Flightline Drive
> Spring Branch, TX 78070
> brian at lloyd.com <mailto:brian at lloyd.com>
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