[GPS_Standard] GPS Receiver question

[Graham / KE9H]

Bob:

Once the UT+ receiver has surveyed its location accurately
(which takes a minimum of four sats) for several hours, then
is put into the timing mode, it will generate a usable timing
signal with only one satellite tracked.  If it is in the
navigation mode, then it needs at least three to provide
a usable timing signal.

It only calculates a solution for four at a time, no matter
how many it is tracking, so I suspect that the answer to
your second question is four with good geometry.  It will
always select what it judges are the best four from a
geometry standpoint from the total set tracked.  It is more
dependent on the geometry than the number.  You are
just more likely to have four with excellent geometry,
the more total you are tracking at any given time.

Best geometry would be three equally spaced around
the horizon, 120 degrees apart, and one straight overhead.
This is why antenna placement matters.  An ideal system
would be able to see the horizon in all directions.

You can improve accuracy with a good antenna location,
particularly if you can get rid of any signals
that arrive as a reflection.

If you are looking for more precision, you need a receiver
with less jitter.  The Oncore UT+ will give you a jitter correction
value (negative sawtooth) for each pulse as part of the
RAIM status message, if you ask for it, but you will need a more
sophisticated system to make the best use of it.

The M12+ or M12M have less jitter or granularity
than the UT+ because they have a much higher CPU clock frequency.
The lowest jitter would be the M12+ or M12M using its jitter
correction value, but once again, you would need a more
sophisticated system (for instance using a phase detector
rather than a counter) to make the best use of it.

--- Graham / KE9H

==

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?
>
> Best regards, Bob K7HBG
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