"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

"Meindert Sprang" wrote in message
...
"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


Tried a Google search for "gps speed doppler" and got the following message:

Your search - "gps speed doppler" - did not match any documents.

Suggestions:
- Make sure all words are spelled correctly.
- Try different keywords.
- Try more general keywords.
Also, you can try Google Answers for expert help with your search.

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


"Larry W4CSC" wrote in message
...

GPS receivers only provide 3 pieces of information. Latitude,
Longitude and Altitude....the 3 dimensions in space. All other
information (speed, heading, COG, VMG, etc.) are all derived by the
computer monitoring the changes in these 3 dimensions over
time.....many seconds. That's why it takes so long for it to change
heading or speed or VMG or other derived outputs when you make that
turn or come about.

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;




Larry W4CSC

Is it just me or did the US and UK just capture 1/3
of the world's sweetest oil supply? What idiot wants to
GIVE IT BACK?!!
If you want a good DGPS I would suggest Trimble. Really execllent.

Rick

Oops....I also forgot TIME. GPS does provide very accurate TIME to
make the calculations in my other post....

Sorry....(blush)

On Mon, 26 Jan 2004 21:12:28 -0500, "wg992000"
wrote:

Does anyone know if there is a set relationship between the accuracy / DOP/
Differenctial indicated on the GPS page to the accuracy of the compass
direction? ( of the GPS)

ie. Trying to determine how far off the compass rose would be off if WAAS
sat's were being received and there was high accuracy.

Kind of new at this. Any thoughts appreciated.



Larry W4CSC

Is it just me or did the US and UK just capture 1/3
of the world's sweetest oil supply? What idiot wants to
GIVE IT BACK?!!

Larry W4CSC wrote:
Oops....I also forgot TIME. GPS does provide very accurate TIME to
make the calculations in my other post....

Sorry....(blush)

On Mon, 26 Jan 2004 21:12:28 -0500, "wg992000"
wrote:

Does anyone know if there is a set relationship between the accuracy
/ DOP/ Differenctial indicated on the GPS page to the accuracy of
the compass direction? ( of the GPS)

ie. Trying to determine how far off the compass rose would be off
if WAAS sat's were being received and there was high accuracy.

Kind of new at this. Any thoughts appreciated.



Larry W4CSC

Is it just me or did the US and UK just capture 1/3
of the world's sweetest oil supply? What idiot wants to
GIVE IT BACK?!!


The "compass" in a GPS is surely historical, it tells you where you've been,
not where you are going? A very rough comparison with the magnetic compass
might indicate if the latter had major errors, but compass swinging using
GPS, someone must be kidding! Much better to use transits, or a hand bearing
compass.
--
Remove "nospam" from return address.

Thanks for all the input -
It was the swinging the compass input I was after.

Thought process was that maybe with decent sat reception - swinging the
compass (adjustments and compass card) may be easier and more accurate with
the GPS then using traditional methods i.e.. lining up bearing points,
shadows etc with my 13 year old at the wheel and me trying to do this. Have
a 21 coastal boat with compass in 5 degree increments. Sounds like the best
idea is stick with traditional methods or farm it out. In any case thanks
for all the help and thoughts.


"Larry W4CSC" wrote in message
...
Oops....I also forgot TIME. GPS does provide very accurate TIME to
make the calculations in my other post....

Sorry....(blush)

On Mon, 26 Jan 2004 21:12:28 -0500, "wg992000"
wrote:

Does anyone know if there is a set relationship between the accuracy /
DOP/
Differenctial indicated on the GPS page to the accuracy of the compass
direction? ( of the GPS)

ie. Trying to determine how far off the compass rose would be off if
WAAS
sat's were being received and there was high accuracy.

Kind of new at this. Any thoughts appreciated.



Larry W4CSC

Is it just me or did the US and UK just capture 1/3
of the world's sweetest oil supply? What idiot wants to
GIVE IT BACK?!!

On Tue, 27 Jan 2004 20:17:32 -0500, "wg992000"
wrote:

Thanks for all the input -
It was the swinging the compass input I was after.

Thought process was that maybe with decent sat reception - swinging the
compass (adjustments and compass card) may be easier and more accurate with
the GPS then using traditional methods i.e.. lining up bearing points,
shadows etc with my 13 year old at the wheel and me trying to do this. Have
a 21 coastal boat with compass in 5 degree increments. Sounds like the best
idea is stick with traditional methods or farm it out. In any case thanks
for all the help and thoughts.

I still like the idea of using the charts and local ranges across
Charleston Harbor......

Wouldn't it be nice if there were some kind of exact crossing ranges
setup for just compass swinging in some out of the commercial shipping
channel place. Two ranges pointing into an area unobstructed,
crossing in the middle. One N-S range and one E-W range with markers
on both ends so you could go either direction and KNOW you were 0 or
90 or 180 or 270.


Larry W4CSC

Is it just me or did the US and UK just capture 1/3
of the world's sweetest oil supply? What idiot wants to
GIVE IT BACK?!!

In article ,
(Larry W4CSC) wrote:

Wouldn't it be nice if there were some kind of exact crossing ranges
setup for just compass swinging in some out of the commercial shipping
channel place. Two ranges pointing into an area unobstructed,
crossing in the middle. One N-S range and one E-W range with markers
on both ends so you could go either direction and KNOW you were 0 or
90 or 180 or 270.

Alot of Coastal Towns have such Ranges setup out here in the west.
In Seattle, all the compass rebuilders use the same range that is
setup in Lake Union. In the spring the whole Seattle Based fishing
fleet can be seen out there doing compass adjusting.

Bruce in alaska
--
add a 2 before @

Charleston needs one on the left coast. Thanks, Bruce.


On Thu, 29 Jan 2004 19:38:37 GMT, Bruce in Alaska
wrote:

In article ,
(Larry W4CSC) wrote:

Wouldn't it be nice if there were some kind of exact crossing ranges
setup for just compass swinging in some out of the commercial shipping
channel place. Two ranges pointing into an area unobstructed,
crossing in the middle. One N-S range and one E-W range with markers
on both ends so you could go either direction and KNOW you were 0 or
90 or 180 or 270.

Alot of Coastal Towns have such Ranges setup out here in the west.
In Seattle, all the compass rebuilders use the same range that is
setup in Lake Union. In the spring the whole Seattle Based fishing
fleet can be seen out there doing compass adjusting.

Bruce in alaska
--
add a 2 before @

Larry W4CSC

Is it just me or did the US and UK just capture 1/3
of the world's sweetest oil supply? What idiot wants to
GIVE IT BACK?!!

"wg992000" wrote in message ...
Thanks for all the input -
It was the swinging the compass input I was after.

Thought process was that maybe with decent sat reception - swinging the
compass (adjustments and compass card) may be easier and more accurate with
the GPS then using traditional methods i.e.. lining up bearing points,
shadows etc with my 13 year old at the wheel and me trying to do this. Have
a 21 coastal boat with compass in 5 degree increments. Sounds like the best
idea is stick with traditional methods or farm it out. In any case thanks
for all the help and thoughts.


Just a thought - why not get a fluxgate compass??? They compensate
automatically, usually by steaming in a large circle slowly, for
boat/ship/vessel deviation and compass swinging is therefore not
required.
I would have though that by now we would be seeing more small gyro
compasses, which of course always indicate true North, removing both
deviation and variation.