Re: Interfacing B&G GPS & Autopilot


2-4-2002 Hi John: Sorry to be so slow to repsond.
This theoretically should have been an easy project
but it turned out to be harder than expected due to
very poor documentation of the NMEA interface by
Raytheon and B & G. A couple of warnings are in order. 1.
Radio frequency interferance (RFI) evidently can cause
the NMEA interface to glitch so careful routing of
properly shielded and grounded wire is important. 2. Use
twisted pair shielded high quality wire, avoid running it
right next to the SSB or VHF antenna cables or other
high current 24 vdc power wires, and ground the shield
at only one end of the wire run (I grounded mine at
the Hydra 2000 NMEA display cable). First the
connections at the Raytheon autopilot computer. You are going
to be feeding the NMEA heading information to the B
& G so that the Hydra 2000 can calculate true wind.
You use the "NMEA output" from the Raytheon computer
(this is located in the cupboard above the sink,
between the 220 VAC and 24 VDC circuit breaker panels and
is mounted on the forward side of the cockpit
bulkhead on which the helm wheel is mounted). The cover is
removed by depressing two tabs on either side of the
cover and sliding it downward. The wires should be
tinned, the shield trimmed off and covered with heat
shrink within about two inches of the terminal strip and
they are inserted by pushing down on the tab and
sliding the wire into the terminal hole. Just look at the
other wires to get the direction of the hole. Route the
wire towards the port side, then via the access tubes
into the access area behind the analog B & G
instruments via the sliding ceiling access panel in the
kitchen. Use one of the the un-used conduits to thread the
wire into the starboard quater-birth area. Then by
removing a small piece of trim in the bookshelf area above
the nav station hanging locker you can route the wire
into the nav station area. Leave enough slack to allow
the rack system to be removed easily. Attached is the
info from the B & G technical support: DO NOT ATTEMPT
TO USE THE NMEA INPUT OUTPUT terminals on the Hydra
processor (i.e. the B & G computer) Instead the NMEA
connections must be made through a NMEA FFD on HYDRA
systems.<br><br>B & G tech support states: The solution will be to
locate your NMEA FFD, and connect the wires from<br>your
Raytheon as follows:<br><br>Raytheon <br><br>NMEA Output
(+) Brown<br>NMEA Output (-) Blue<br><br>NMEA FFD<br><br>NMEA
Input (+) Violet<br>NMEA Input (-) Black<br>The
wire shield is grounded by connecting to the other
grounds at the hydra processor. <br><br>The above wires
are from the cable coming from the Hydra 2000
display. You will find that they are capped. Just pigtail
them together as indicated. <br><br>Best
regards<br><br>Alan Titterington<br>Technical Support
Group<br>B&G/YEOMAN<br>Tel: +44 (0)1794 510013<br>Fax: +44 (0)1794
518077<br>Mobile: 07740 543182<br>e-mail:<br><br><br>Finally you must set the heading node on the Hydra 2000
display. This is described in the B & G manual. Basically
you go into a configuration menue on the Hydra 2000
and set the heading node for NMEA (if I recall
correctly it is node 96). Hope this helps. You can do
additional interfaces but that gets a little more
complicated. Sincerely, Gary

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