[hpsdr] Hermes/Anan 10 Drift?

[Mike Monnier]

"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 50Ξ©, not 100Ξ©. Change that an you won't have any problems with using your external reference.Β "

I see some odd type from time to time on this reflector. In your post (cut and pasted above) you are talking about R 141. A resistor I assume and it should be 50 ohm? Not 100 ohm? Is that right? I am not able to replace an SMT component on a 5 layer board. I'll have to think about this. What is the power rating of R141? I may have to find a SMT tech to do this for me. I have two Anan-10 rigs. They both will need the modification. 

Your reply is exactly what I was looking for Brian. Thank You Very Much for your help. 

Best Regards,
Mike
www.w8bac.com


From: Brian Lloyd 
Sent: Thursday, March 14, 2013 4:57 PM
To: Mike Monnier 
Cc: hpsdr at lists.openhpsdr.org 
Subject: Re: [hpsdr] Hermes/Anan 10 Drift?


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.Β 


  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.Β 


(Sorry, IΒ accidentallyΒ typo'd send.)Β 


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 50Ξ©, not 100Ξ©. Change that an you won't have any problems with using your external reference.Β 


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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