would
give good resolution down to at least 2 to 3 knots.

Exactly Kevin Monahan's point. At low speed, creeping through fog, you will
not get a stable heading readout. I have a Garmin 182C plotter with WAAS.
Below 2 knots I start to see the "compass" heading wandering.
Kevin's book is quite recent and takes into account the current situation.
I'm planning on purchasing the Raymarine Seatalk/NMEA conversion box so that
I can feed my Autohelm fluxgate compass heading to my JRC radar. The JRC
has two NMEA inputs, one for GPS and one for Compass. Internal software
selects the Compass heading input over any GPS heading input.
Maybe this isn't necessary a lot of the time but I'd like to be able to rely
on what the radar is showing at all times.

"Bruce in Alaska" wrote in message
...
In article tZRfd.10435$df2.5362@edtnps89,
"Gordon Wedman" wrote:

In " The Radar Book - Effective Navigation and Collision Avoidance " by
Kevin Monahan, he points out that the compass bearing given by a GPS will
be
unstable at low speeds. If you want your radar to show proper compass
bearings and work in the North-up/Course-up modes he says you must
connect
to some type of fluxgate or gyro compass. So if you just connect your
GPS
NMEA output to your radar it seems you may not get correct heading
information while creeping along at low speed, for example, in fog.

That would very much depend on the GPS, its Position Update Rate, and
internal Math Capabilities. I would suspect that any GPS that updates
faster than every .5 Sec, and has a good floating point processor, would
give good resolution down to at least 2 to 3 knots.

Bruce in alaska
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add a 2 before @