Neg/pos

[JSK]

I am in the throws of installing a JRC 1500 Radar. the insruction manual suggests the prefered connection for giving a heading is through a flux gate compass, rather than the GPS. I have the autohelm 4000 and I would like to connect to this. The JRC manual says to connect to the compass positive and negative - there are 4 wires going from the autohelm 4000 control unit to the compass and what I would like you to know is which wires are the negative and positive, or can I connect to the NMEA negative and positive.

Thanking you in anticipation,



<hr width=100% size=1>

 

[Talbot]

The one disadvantage would be that you would have to have the autopilot switched on each time you need to use the radar.

<hr width=100% size=1>

 

[davidwf]

You should just connect it to the NMEA positive/negative on the autohelm control unit.

<hr width=100% size=1>

 

[bedouin]

I'm not sure that the AH4000 outputs NMEA from the Compass.

<hr width=100% size=1>

 

[JSK]

Thankyou for your reply.If I connect to the NMEA on the autohelm can I also connect to the NMEA On My GPS as well ,so as to still recieve data when the Autopilot is not turned on

<hr width=100% size=1>

 

[davidwf]

Nema connectiosn

Just looked at the St4000 manual it does not have a NMEA out only an in, so unless you have a Raymarine Multi or fit a Seatalk to NMEA bridge you cannot get the compass heading data out of the ST4000. These cost around £125. have a look on Ebay they sometimes appear there.

Re you question on NMEA:-
You can connect one talker to 4 or 5 listeners ie fan out one talker, but you cannot connect two talkers to one listener ie fan in. There are some multiplexers available that allow this

<hr width=100% size=1><P ID="edit"><FONT SIZE=-1>Edited by davidwf on 28/04/2004 20:17 (server time).</FONT></P>

 

[JSK]

Is it for the nornal to use the Gps NMEA output for heading info?.I assume this will only be a problem if not making way ,or are there other disadvantages to this

<hr width=100% size=1>

 

[LadyInBed]

Autohelm output is ‘SEATALK’ so to use 'North Up' radar you either pay loads of dosh for a seatalk / nmea converter, a separate fluxgate compass with an nmea output or you settle for ‘Head Up’ display and save your money.

<hr width=100% size=1>

 

[JSK]

Thanks for reply, Will I be able to use north up if connected to GPS NMEA output ?

<hr width=100% size=1>

 

[LadyInBed]

Re: north up

No, only Head up without a fluxgate input

<hr width=100% size=1>

 

[Talbot]

Your GPS will not give you "heading" info either. The GPS course is ship's course over land taking into account leeway and tide. If there is a lot of tide and leeway but speed is low, there could be more than 50 degrees difference between course through the water and course over the ground (i.e. GPS course). The only reason for putting a fluxgate heading into the radar is to allow a "north-Up" display - you cannot do this with a GPS course.

<hr width=100% size=1>

 

[john_morris_uk]

I think that accurate heading information helps the Raymarine system calculate MARPA (ie course, speed, and closest point of approach of a selected target etc) more accurately. Raymarine strongly recommend a more accurate gyro compass for their radar's. if I remember correctly. (Its why we just bought a pilot computer with a gyro built in for when we upgrade the radar.)

However if the Radar loses this info it will still work - it just won't allow you to switch to North up display.

<hr width=100% size=1>