[time-nuts] Trimble Nortel GPSTM Boards

[Jim Sanford]

Bob:
Well, this is discouraging.  The receiver seems to work -- receives the 
sats it should.  Seriously doubt there's any multipath out here in the 
boondocks.  Maybe some tree absorption at very low elevation, but very 
little in the way of reflectors.  I'm on 10 acres on a hillside, with 
trees in the distance.
Jim

On 8/2/2013 9:24 AM, Bob Camp wrote:
> Hi
>
> Either a blown receiver (likely the SAW filter) or antenna multi path.
>
> Bob
>
>
> On Aug 1, 2013, at 8:45 PM, Jim Sanford <wb4gcs at wb4gcs.org> wrote:
>
>> I am seeing the same thing -- big jumps every single time a satellite is counted or not.  Elevation mask 10 degrees, which should be very good and stable for my location.  The unit also insists on converging to a bat altitude, then after a while declares stored position bad . ..  then declares position good, even with bad altitude.
>>
>> Ideas appreciated.
>>
>> Jimwb4gcs at amsat.org
>>
>> On 8/1/2013 6:31 AM, Bob Camp wrote:
>>> Hi
>>>
>>> You may have your elevation mask set to low for your antenna or a multi path issue from some other source.  If the survey location is good to under a meter and the signals are good, there should be very little shift as sats are picked up or dropped.
>>>
>>> Bob
>>>
>>> On Aug 1, 2013, at 5:09 AM, GandalfG8 at aol.com wrote:
>>>
>>>> Hi Charles
>>>>
>>>> Thanks for your comments, the surveyed position on this is looking pretty
>>>> good but what I have now realised is that the severity of the jumps  seems
>>>> very much related to the number of sattelites being tracked.
>>>>
>>>> Switching from 8 to 7, or 7 to 8, sats seems to produce the biggest  step
>>>> change whilst switching in either direction between 5 and 6, for  example,
>>>> doesn't seem to show up at all on the monitored DAC voltage.
>>>> Ok, I take that back, it does still seem to depend on the number of sats
>>>> being switched between but I've just seen a switch from 5 to 4 sats induce a
>>>> very noticeable step change in DAC voltage, so the relationship  doesn't
>>>> appear to be linear.
>>>>
>>>> Unfortunately I need to power this down now for a few days but  will
>>>> investigate more later.
>>>>
>>>> Regards
>>>>
>>>> Nigel
>>>> GM8PZR
>>>>
>>>>
>>>> In a message dated 01/08/2013 09:45:24 GMT Daylight Time,
>>>> charles_steinmetz at lavabit.com writes:
>>>>
>>>> Nigel  wrote:
>>>>
>>>>> at times I'm seeing very noticeable step changes in the DAC  voltage
>>>>> on this one as that happens.
>>>>>       *   *   *
>>>>> I am a bit surprised by the extent, a  Mark Sims online plot from
>>>>> 2012 shows some correlation on an NTGS50AA  but not as noticeable as
>>>>> this, and I  don't recall seeing  anything quite so pronounced on a
>>>> Thunderbolt.
>>>>
>>>> IME (with TBolts), the  magnitude of the DAC steps with constellation
>>>> changes varies with the  accuracy of the positional data used by the
>>>> GPS.  To a point, the  more accurate the survey, the smaller the DAC
>>>> jumps will be.  (Other  errors prevent reducing the
>>>> constellation-change DAC steps to  zero.)
>>>>
>>>> Mark has commented here on survey accuracy, and the methods he  used
>>>> in Lady Heather to maximize it.
>>>>
>>>> Best  regards,
>>>>
>>>> Charles
>>>>
>>>>
>>>>
>>>>
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