Re: rooftop antenna range

DanS <t.h.i.s.n.t.h.a.t@xxxxxxxxxxxxxxxxxxxxxx> hath wroth:

Hey Jeff,

Huh? I guess that's me. 14 hour work day today. Dinner at midnight.
Brain is gone. I guess I'm ready to answer questions.

GPS boards that belch raw data ? Is that individual satellite info vs.
ascii GPS strings ? Interesting.

Disclaimer: I are not an expert in GPS.

To do DGPS, you need a GPS that will belch individual satellite
doppler delays (also known as raw data), and not NEMA-183 ASCII text.
DGPS corrects on a per satellite basis and needs the raw data to do
the corrections.

I didn't really think DGPS was really
necessary any more.

GPS accuracy is a subject of considerable contention. There are a
bunch of web sites that offer test results for various technologies.
One of many:
http://users.erols.com/dlwilson/gps.htm
My guess, opinion, and experience is:
Uncorrected GPS with clear view: 5 to 15 meters (1 sigma)
Uncorrected GPS with lousy view: 10 to 30 meters
GPS with WAAS: 2 to 7 meters
DGPS with 50 mile baseline: 2 to 5 meters
DGPS with 1 mile baseline: 0.1 to 2 meters
If you want cm accuracy, you gotta have a local DGPS transmitter. One
big problem is that the final accuracy is totally dependent on the
accuray of the DGPS antenna location. cm accuracy is worthless if the
location of the correcting GPS is not located with the same precision.
So, I get to do some precision surveying.

I used to work for GLB Electronics, since your a ham, you may have heard
of them. (The owner designed the first synthesized radio gear for hams
back in the 70's, the GLB Channelizer.)

I plead ignorance. I was doing lots of commercial radio in the
1970's. I was also out of the country much of the early 1970's.
To keep my sanity, I completely ignored ham radio until about 1993.
I even intentionally let my ham license expire.

Anyway, before the GPS 'error' was turned off, people doing DGPS was
GLB's bread and butter providing narrow-band data link's for the
differential signal.

It's a common service. However, there are now several free and open
DGPS systems on the air in the Monterey Bay area. There's also free
post mortem corrections available on the internet. I have some
applications in mind which I don't wanna disclose.


--
Jeff Liebermann jeffl@xxxxxxxxxxxxxxxxxxxxxx
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
.