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GPS antenna question

Brookelise

Member II
We plan to set up our GPS chartplotter so that it can be used either at the helm or nav station. There’s a concern that splitting the antenna cable (so that it goes to fittings for the GPS at the nav station and helm) could degrade the antenna signal. Then there’s the question of how to split it, with a regular three-way cable splitter, which would degrade the signal (but how much?), or with a manual two-way antenna selector (from two GPS stations to one antenna), or with an automatic antenna selector (again, two GPS stations to one antenna, but the signal would be read automatically, switching to the GPS station in use).

Garmin actually recommends none of the above. They recommend not even removing the fitting at the end of the cable, never mind splitting the cable. Their solution would seem to be buying two antennas. Removing the fitting voids the guarantee, even though many people would have to remove it to thread it through various places (deck, pedestal guard, etc.).

The manual two-way antenna selector is on p. 33 in the 2007 West Marine catalogue, btw, along with the automatic one, under coax, connectors & cable. Would the automatic one, designed really for two VHFs, work with a GPS antenna?

And just for good measure, here’s another question: We have a Raymarine repeater at the helm, and we wonder whether the chartplotter could be linked in a series with the repeater and autohelm. The repeater gives data from the chartplotter. Everything is NMEA, but the GPS instructions show only one link – to a repeater or to an autohelm. Would the link work in a series, from chartplotter to repeater to autohelm, or from autohelm to repeater?

Any advice on this?

Thanks,

Brooke
 

Mike.Gritten

Member III
I am not familiar with the units you are installing but, IIRC NMEA devices do not use coaxial cable like VHF or SSB antennas, and therefore could not (should not?) utilize the 2 way switches you refer to. NMEA has devices that area either "talkers" or "listeners". Your GPS "antenna" would be a talker. Multiple devices can "listen" to the GPS on your NMEA network. Therefore, I think that all you need is to run the small conductor cables into whatever junction box Garmin sells, and both your plotters should be able to use the NMEA sentences sent by your GPS. Good luck, and let us know how you make out.
 

Howard Keiper

Moderator
Pay attention to what Garmin tells you. No matter what combination of cables, switches or connectors you engineer, the performance of your GPS will suffer...not in a catistrophic sense perhaps, but will suffer none the less.

Your chart plotter is a listening device, it does not provide data to anything...ditto your Autohelm. Both devices accept positional data from your GPS, a talking device; it does not accept data from anything...as Mike points out.

Howard Keiper
 
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