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[aprssig] differential corrections available to public(insome places)

Rich Garcia k4gps at arrl.net
Tue Mar 15 00:00:19 UTC 2005

Initially that is what was tested and as Gerry stated back then we needed
DGPS stations at 60 or so mile intervals
for optimum coverage and accuracy. The other issue was 15 or so second
updates were necessary and here for the 60
mile range that would mean 3 or so hops that a) Adds time delays and b)
saturates the channel (maybe not fully) but
quite a bit when you think of one packet generating 2 others every 15
seconds plus the traffic. Gerry...what would
it be like now, how far would the correction be valid for ?

I have one of the DGPS stations here that I never quite fully completed in a
diecast box, all I need to do if finish
the interface connector and power connector and find the software for it. I
would be willing to set it up in this
area if there would be interest in that again but with the growth of APRS 15
second intervals would need to go on another
frequency and if that were the case I may as well bump it up to 8 seconds to
make sure it got through, the DGPS channel
would not have a digi on it so range would be limited.

But as someone else pointed out, do we need THAT much accuracy ? Think of
what the accuracy of the maps we use are and
what benifit we would get for better accuracy.


-----Original Message-----
From: aprssig-bounces at lists.tapr.org
[mailto:aprssig-bounces at lists.tapr.org]On Behalf Of Jim Lux
Sent: Monday, March 14, 2005 12:52 PM
To: Robert Bruninga; aprssig at lists.tapr.org
Subject: Re: [aprssig] differential corrections available to
public(insome places)

At 08:49 AM 3/14/2005, Robert Bruninga wrote:

> >>> "Jim Lux" <jimlux at earthlink.net> 3/14/05 10:56:52 AM >>>
> >> That may all be old or obsolete, but it is how we were
> >> recommending it back then.  I think we were suggesting
> >> that the RTCM104 be on a different 2m freq so that it
> >> couild be real-time full operations without any QRM to
> >> 144.39.
> >> de WB4APR, Bob
> >But, if it's on a different frequency, then existing TNCs and
> >radios, which are single channel centric, wouldn't be able
> >to gain the benefit of more precise positions.
>All radios can operate with one TX and a different RX.
>Its no different than 2m voice through a repeater. you
>liisten on one freq and TX on another.

But then your radio won't hear all the other APRS stations transmitting on
144.39.  I was proposing the distribution of real time corrections within
the framework of APRS, not as a standalone accuracy enhancement (for which
there are a multitude of other approaches).

I suppose you could set up a high site to transmit two streams, one on
144.39 with just position reports that you're basically digipeating and the
other on something else that has both APRS messages and real time
corrections merged, but it's not clear that the second frequency wouldn't
wind up just as congested.  I guess it would have dupe's removed, and there
wouldn't be as much contention from other mobile's transmitting.


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