[time-nuts] Adafruit (MT3339) problems today

Bob Stewart bob at evoria.net
Fri Apr 11 16:49:40 EDT 2014

Hi Magnus,

Yeah, there's no getting over the fact that it's a cheap $30 (or whatever it was) nav receiver.  But I think the "walkabout" issue has been resolved.  I think this thing is going to be OK for me, but I certainly wouldn't even give it a glance for professional use.  Now that I've got the basic PLL code working with the new TIC, I'm starting to expand what I'm monitoring.  There seems to be such a close connection between when it wanders around and when there are blips on the phase that I'm going to add position change monitoring shortly.  Who knows?  Maybe I can tune it out with the "poor man's sawtooth" that I've asked about.  Yeah, I know.  Just wrinkle your nose or look away in disgust if it bothers you.  =)  My goal is to see what I can get out of this; not what I can get for a few hundred dollars more.  The project is more important to me than the result.  I don't really have a concrete use for an accurate timebase.  But, I have to say
 that after I've learned what I can with this, I'll probably look for something better; like maybe an LEA-4T or whatever I can get for cheap.  I don't like the UT+ I have.  Comms is overly finicky to get started.  In fact, I don't even have a reliable way to do it after a cold start.   And I don't like the +/- 52ns sawtooth.


> From: Magnus Danielson <magnus at rubidium.dyndns.org>
>To: time-nuts at febo.com 
>Sent: Friday, April 11, 2014 2:49 PM
>Subject: Re: [time-nuts] Adafruit (MT3339) problems today
>On 10/04/14 23:48, Bob Stewart wrote:
>> My Adafruit has gone walkabout again.  This is a different unit than the one I spoke about some months ago.  It's been about 150 ft from my actual location, which has, of course, made a mess of my GPSDO.  Well, at least it verified my "unlock" code.  I did a POR and it seemed to come home, but now it's off to the races again.  Has anyone else seen this behavior with this device?  The only particular anomaly I can see is that it uses satellites close to the horizon for position fixing.I'm getting a reported SNR of 39 at 5 degrees elevation and 37 at 3 degrees, though I notice the sat at 3 degrees is not being used to calculate position.  I never got around to finishing the choke ring antenna with those pie pans.  Maybe that needs to move higher on my priority list.
>Can you raise the elevation limit? Low elevation causes many problems, 
>multi-path is certainly one but massive tropospherical delay errors.
>Maybe we should look at a bare minimum requirement for GPSDO-use?
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