[time-nuts] Adafruit (MT3339) problems today
bob at evoria.net
Fri Apr 11 20:49:40 UTC 2014
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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