[hpsdr] Hermes/Anan 10 Drift?

[Brian Lloyd]

On Thu, Mar 14, 2013 at 1:52 PM, Brian Lloyd <brian at lloyd.com> wrote:

>
>
> On Thu, Mar 14, 2013 at 1:20 PM, Mike Monnier <w8bac at comcast.net> wrote:
>
>> ***** High Performance Software Defined Radio Discussion List *****
>>
>>
>> **
>> My Apache Labs Hermes/Anan-10 has, what looks like, frequency instability
>> or
>> drift that seems to be caused by temperature changes.
>>
>
> Yes, you are right. I discovered the problem a month or so ago and worked
> with Phil and the folks at Apache Labs (with whom I am quite impressed and
> with whom I will happily continue doing business) about it.
>
> First, yes, you will see what appears to be temperature instability on the
> internal 10MHz reference. If you look at the absolute numbers you will find
> that this "instability" is well within the 1ppm specification. The
> worst-case error I ever saw was just short of 2Hz at 10MHz, or 0.2ppm.
> Quite a bit better than spec -- but still annoying. My first inclination
> was the that there was a problem with the PLL that locks the 122.88 MHz
> clock to the 10MHz reference. That was not the case. The problem turns out
> to be the way that the 10MHz internal reference is temperature compensated.
> Apparently it is digitally compensated and therefore the corrections are
> quantized, hence the sudden jumps. Yes, it is annoying, especially if you
> are a frequency measurement geek like me. But that does not mean it doesn't
> meet spec or that it can't be used, even for applications like WSPR.
>
> The other issue is the use of external reference input.
>

(Sorry, I accidentally typo'd send.)

There was a bad value in the Schmidt-trigger squaring circuit for the 10MHz
reference input. R141, the emitter resistor of the differential pair, has
the wrong value. It should be 50Ω, not 100Ω. Change that an you won't have
any problems with using your external reference.

The ANAN-10 is a good FMT platform with a good 10MHz external reference. I
use either an LPRO-101 Rb reference or a Trimble Thunderbolt GPSDO with
mine. Works like a champ.

-- 
Brian Lloyd, WB6RQN/J79BPL
3191 Western Dr.
Cameron Park, CA 95682
brian at lloyd.com
+1.767.617.1365 (Dominica)
+1.916.877.5067 (USA)
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