[GPS_Standard] GPS Receiver question

[Glenn Elmore]

In addition to the comments posted, it seems to me that the question of
GPS receiver jitter is likely dwarfed by the DFLL jitter. The capture
circuit in the PIC being used is a state machine which runs from the PIC
CPU clock.  The actual captured value must occur at the same state/phase
of the CPU clock phase (four internal 8 MHz Clock cycles per instruction
clock). This behavior is at the root of the +- 4 count ambiguity one
sees on the freq error count - even when counting a perfect 1 PPS
derived with 7 decade dividers from a 10 MHz crystal.

 

This DFLL jitter is effectively superimposed on any 1 PPS jitter coming
from the GPS receiver and, with the 8 MHz RC clock being used in v4
code, this means about +-.5 us jitter + GPS jitter  = total jitter.

 

I don't know what the specs are on all GPS receiver but I don't think
many are worse than a half microsecond are they. This is *jitter* we are
discussing, not absolute accuracy.

 

Glenn

N6gn

 

 

k7hbg @dslextreme.com wrote:

> Hi Everybody;

> 

>  I have a Moto. R5122 Oncore receiver in use with Bert's controller 

> board. I was wondering if anyone could tell me how many tracked "space


> vehicles" (you gotta love the jargon) is needed as a *minimum* to 

> assure proper operation of the system.

>  I would also like to know what is the maximum number of SV's after 

> which no difference is realized.

> I was looking at the new oncore m12m receiver OEM module and thinking 

> would tracking 12 SV's yield any more precision?

>  In other words, how much is too much?