cognisense wrote in news:30dfe109-f7f6-48a3-958c-
:

Yes. It's very interesting that you experienced similar jumps with
your old setup. I've only got one display and one GPS, but it is
possible that the jumps are being caused by something external to the
display. Another poster here had mentioned cable problems, and that's
worth looking into. I'll report back if I find anything.


Another GPS problem bears thinking about in your situation, also.....

I noticed in your video your close proximity to tall land masses, the
mountains of SW BC. Not much is ever said about it because most don't
want to believe GPS is fallible, but it is....

GPS is an analog system of precisely timed pulses, not unlike Loran C
was but with much heavier computing power behind it. It relies heavily
on the direct path of these microwave pulses for its position fix.
ANYthing that reflects radio waves coming from the satellites to its
receiver, causes the pulses to arrive LATER than they should. This
confuses some receivers much worse than others, especially the
expensive, higher sensitive ones who, I think, stupidly have much more
receiver sensitivity than they should. The better receiver can hear
these reflections better than the cheap ones with lots less antenna.
Once confused by the arrival of odd-timed pulses, duplicate pulses,
etc., it's up to the software to average out and discriminate against
erroneous pulses. It's supposed to pick the FIRST set of pulses, the
direct ones, not later arriving pulse trains from the same satellite.
But, alas, sometimes that doesn't happen. If the reflection is all it
hears, its algorithms take that as the primary pulse and switch the fix
from the triangulation accordingly.

You can try this, yourself, with your handheld GPS no subject to the
Raymarine nonsense. (I don't like Raymarine, either, so I'm not afraid
to speak up.) Take your handheld with you when you go to a restaurant
with big windows and an overhead RF opaque roof of metal. When you're
situated at your table, away from the windows is best to see its effect,
turn on the GPS and let it initialize to what it hears. Through the big
windows, transparent to the RF, the GPS starts picking up signals
bouncing off moving vehicles, adjacent buildings, towers, light poles,
any reflective surface. It drives the software crazy because it sees
almost no direct signals because the roof attenuates or blocks it
entirely. Turn on the GPS' bread trails and zoom in as tight as it can
go. Eat your breakfast and let it run an hour. Watch the "track" of
it. It's useless for navigation, too. This is a trait of GPS, not
Raymarine. Now, make SURE the GPS antenna isn't NEAR any metal objects
that can obscure large parts of the sky. I've found GPS antennas
mounted too close to masts, stancions, metal plates, wiring, all opaque
to that DIRECT signal. As the boat turns, the direct signal, like the
sun coming out of an eclipse, which is exactly what is happening,
suddenly appears from behind the opaque object. The software says
"WHOA! The timing to THAT bird has just changed RADICALLY! I better
compensate, and compensate it does....making its display JUMP like you
observe. Pick the GPS with the "Crazy Track" off the table and sit it
in one of the big windows on the window sill. It suddenly can see all
the direct signals that were eclipsed by the roof in one direction.
Watch the fix point. It jumps!

I had a GPS problem with a mounted Garmin whos antenna was on top
surface of the stern. He had the antenna in the clear....well, except
for the STERN NAV light it was nearly touching. The whole sky in one
direction, probably about 100 degrees, was BLOCKED by the metal mount of
that light. After we'd moved it to a more open position, the fix quit
jumping around whenever the boat turned that blind eye away from a fix
bird. We moved it about 8". The part of the sky the light blocked was
now only 20 degrees, which it seemed easily to compensate for because it
could see more birds, directly.

This is another cause of "jumping".

GPS is a lot less high tech than the public thinks it is. It's not
Ethernet...(c; That's why it updates SO SLOWLY...once per second. It's
working trying to be accurate in a noisy wasteland of RADIO signals.

This is for your next GPS, not this overpriced Z80-based slowpoke. God,
I can't believe it just BLANKS the screens, even just one, so LONG! I'd
hope if it's receiving crap on Seatalk it would be smart enough to TELL
YOU SO with some kind of error message....not just blank out hoping for
the best.

By the way, Seatalk isn't rocket science. Connect Seatalk data wire
(Yellow) to an RS-232C data in pin (pin 3 on the 25pin/pin 2 on the 9
pin) and hook Seatalk ground to computer data ground pin (7 on the 25, 5
on the 9). (I use little mini clips and made a snooping test cable.)
Boot good old Hyperterm. Save you a dumb terminal ASCII.ht connection
to make it easier to come back. Mine's on my laptop. Plug Seatalk
Hyperterm and look at the data, yourself, as it streams by. At some
point, after it has filled the buffer, pull the plug and look down
through the data for noise and crazy bits. Seatalk isn't encrypted...
(c;

http://www.raymarine.com/raymarine/S...s/raytech/8116
6_3www.pdf
This is the manual for the Seatalk to NMEA converter box Raymarine
sells. Your MONITOR is also a converter box. If you put Seatalk data
into its Seatalk port, it converts and transmits it to NMEA on its NMEA
out ports...IF YOU TURN THE STATEMENTS ON FROM THE MENU TREE! If your
computer is reading NMEA statements from the NMEA OUT port on the
display, and there's crap on the Seatalk port....there'll be crap coming
out of the NMEA port, too.....or none at all for some period of time.

HF RADIO TRANSMITTERS EAT SEATALK in a lot of installations. Even foil
shielded cable doesn't stop it.

Watch either the Seatalk or NMEA data streams as the display just blanks
for long periods of time. If the data looks right...so much for blaming
the cabling for the delay....

Well, it's after 1AM. I'll try to conjure up more when the screen comes
back into focus....tomorrow...(c;

Gnite
It's 1AM, 58F, 2 knot winds SW. Plenty of dock space, albeit a little
pricey for some in the harbor. Drop by, we'll eat Gullah fish and grits
for breakfast.... It was nearly 70F today. I see you like gunkholing.
There's 2200 miles of navigable creeks within 50 miles of this keyboard.
Most you can drop anchor in and never see another soul all weekend!