GPS Query...

[John 32i]

I have recently bought a yacht with a Garmin GPS 120XL installed that doesnt appear to be able to find a satallite, I also have a Raymarine C70 in a locker that appears to be new and never used. I assume that its not worth messing about with the Garmin, which appears to be several years old - I may as well install the Raymarine - thing is will this work with the same aerial as the Garmin - is it just a question of changing the plugs wiring it up and away I go...or is it going to be more complicated?

 

[Talulah]

thing is will this work with the same aerial as the Garmin?

Which aerial are you talking about?
If this is the Garmin GA29 then "No. You can't use it."

 

[John 32i]

GPS mounted on the pushpit - not sure of the actual make, just wondered if they were universal or peculiar to individual units? (its not the GA29 - just googled that one and mine looks differant)

 

[lw395]

I don't know about the Raymarine units, but most Garmin aerials have +5V supplied up the coax to drive a pre-amp. This is pretty standard and you can use car-type GPS aerials with a Garmin GPS.
There are other units, where the 'aerial' is in fact a whole receiver which outputs NMEA data, not an RF GPS signal.

Unfortunately, in my experience, the aerial is the least reliable bit and might well be why the Garmin unit can't see any satellites.

 

[pvb]

You need to find out what sort of GPS antenna you have on your pushpit. The Garmin 120XL uses a passive antenna, as it has a receiver built in to the 120. The Raymarine C70 doesn't have a receiver built in, so it needs an active antenna which outputs GPS data as NMEA (or SeaTalk). If you have a C70 lying around, you ought to use it - they're great plotters.

 

[MoodySabre]

I've got a 120XL. It is very slow to acquire a fix but then keeps it well. Perhaps the connections need looking at.

 

[Elemental]

I've got a 120XL. It is very slow to acquire a fix but then keeps it well. Perhaps the connections need looking at.

Interesting. I have a 120XL that gets a fix in seconds. I wonder if your internal battery has expired and the unit has to attempt to lock onto unknown satellites download a full dataset (ephemeris info) rather than use the last known position and almanac info? - or words to that effect...

 

[MoodySabre]

Thanks Sea Spray. Googling tells its one these Panasonic vl1220 batteries. Screwdriver out tomorrow

 

[minsted]

Also worth checking the antenna - I inherited a Garmin 128 on the boat that wouldn't find a fix - tracked back to the Garmin mushroom antenna, looked fine but totally corroded inside (although difficult to check as you can't open them - finally cut it in half)

 

[lw395]

You need to find out what sort of GPS antenna you have on your pushpit. The Garmin 120XL uses a passive antenna, as it has a receiver built in to the 120. The Raymarine C70 doesn't have a receiver built in, so it needs an active antenna which outputs GPS data as NMEA (or SeaTalk). If you have a C70 lying around, you ought to use it - they're great plotters.

Not exactly a passive antenna, it has a low noise preamplifier built in. and some filters IIRC.
You can use a cheap car gps aerial from ebay to test the receiver, but most of them need to be mounted on a metal 'ground plane' to work at all well.