[time-nuts] Followup (still want a GPS-type NTP refclock)

Said Jackson saidjack at aol.com
Thu Oct 18 22:57:05 EDT 2012


Thanks!

Have fun experimenting
Said

Sent From iPhone

On Oct 18, 2012, at 18:54, Sarah White <kuzetsa at gmail.com> wrote:

> On 10/18/2012 1:20 PM, SAIDJACK at aol.com wrote:
>> Let the GPS average the antenna position over a very long time.
>> 
>> On a good GPSDO one can select the number of averages, and the position  
>> variance before the survey is finished, and the (now very precise) position is 
>> stored in memory.
>> 
>> Indoors this may take a very long time to do (weeks?), but should work too. 
>> The problem indoors is multi path, one never knows where the signal is 
>> coming  from that is seen. Setting up signal squelch in the GPS really helps 
>> with that,  for example the C/No could be set to a minimum of 35dB, and 
>> anything below that  is ignored so only the strongest signals are used.
>> 
>> We made a customer's urban solution work that way, it effectively  deleted 
>> all the multipath issues he had from adjacent high-rises, since the  
>> multipath signal strengths yielded about 20 to 28dB C/No and were thus all  
>> squelched, whereas the direct signals were 35 to 50dB C/No.
>> 
>> bye,
>> Said
> 
> Wow thanks.
> 
> I've never seen such an insightful explanation for dealing with
> multipath signal issues. Fortunately, I'm not doing this for any sort of
> "for profit" purpose / just learning for now. This list really has a lot
> of experts :)
> 
> -- Sarah
> 
> P.S. Sorry for the earlier PGP signatures... In the past 24 hours
> someone pointed out to me, to paraphrase: "most of the people reading
> this list aren't using email systems which make any use of the (rather
> long) message validation blocks"
> 
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