"Larry W4CSC" wrote in message
...
On Tue, 27 Jan 2004 12:34:35 +0100, "Meindert Sprang"
wrote:

I have heard otherwise: A GPS derives it's speed from the doppler shift
on
the received carriers. A very slow averaging filter smoothes the output,
which causes the delay in indicated speed. The filter is there to prevent
erroneous speed indication due to atmospheric disurbances and multi-path
signals.

Meindert


This might be true on some $70K sophisticated survey instrument or
other, but, here at least, our discussion is about GPS operation on a
cheaply-made piece of crap sold to the boating consumer at amazing
markups, not sophisticated electronics. What you're talking about
costs serious money. You won't find that at Waste Marine where price
isn't related to quality.....(c;

Well, the datasheet of my "cheaply-made piece of crap" GPS module, costing a
whopping $70, clearly states the presence of doppler shift data in the raw
datastream I can extract from that module. The used chipset is a very common
one in low end GPS receivers. Do a google search on "gps speed doppler" and
you'll find this info.

Meindert