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Old 05-01-2010, 22:22   #1
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Old Marine-Tech GPS Antenna

I am working on a Whitbey 42 with an old Marine_Tech GPS antena. I had to pull the main mast to replace all the standing rigging.
I called my local electronics friend beforehand and he said the cable would have 6 wires which i could connect to a buss bar (NMEA 183?). He said that this type of GPS had a processor in the unit so the wires would carry data instead of antenna signal. So I cut the wire, which turns out to be a coaxial cable ( i tried to find the wire's source but it went into the engine compartment and through several bulkheads and through hell's half acher . It was getting too expensive tracing it so i cut it.

My question is:

How can i rejoin this GPS Antenna coaxial cable when I step the mast?
Can I use normal coaxial connectors?
Am i screwed?

Thanks in advance.

Pip
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Old 06-01-2010, 02:16   #2
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The cable you cut is purely an antenna feed to the GPS receiver. It will probably carry a DC current to power an amplifier within the antenna itself but won't carry any GPS signal. It can be rejoined using BNC (bayonet), TNC (screw) or maybe PL259 connectors although latter are a little bulky. Try & match the impedance of the cable (usually 75Ω) - a male & female connector are ideal but two male with a back to back female coupler will also work.

Trace antenna wire to GPS receiver & there you should find the six wire cable your friend referred to. You will need more info to identify which two wires carry the NMEA output.

Having said all that it will be a lot simpler & probably cheaper to buy a modern GPS mushroom receiver which can be mounted on the pushpit rail with a single cable run, & pull out the old installation on the mast.
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Old 06-01-2010, 02:30   #3
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You should probably be using MCX or MMCX connectors for GPS aerials, though there are several options. You might consider replacing the whole GPS system with a new GPS mouse, as long as you're not connecting to a plotter or something with an integral GPS decoder which has no NMEA feed. Since you are on a GRP yacht, you should be ok with a modern GPS mouse inside the cabin. The attenuation of GRP is not usually significant.

Given that you haven't found the connected end yet, I'd trace it back from the instruments, and find out what the aerial was actually plugged into. You may be able to do a very simple replacement.

Tim B.
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Old 06-01-2010, 18:33   #4
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Hey Tim and Richard,

Thanks so much for your wisdom.
I got a pair of MCX connectors which should do the job.
I was talking to the local Furuno technician about getting a replacement cable (it had been run on the outside of the mast and was breaking down from UV) and i asked him about MCX connectors for the GPS and he agreed that they would be a lot better than a standard coaxial connector.

It'll be a couple of weeks before we drop the masts back in and I'll let you know how it went.

Cheers,

Pip
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