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Old 28 December 2007, 09:08   #1
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Active GPS aerials

I am running out of enough NMEA outputs to provide feeds to all the various electronics I have bought.
This has got me thinking that if I put an active GPS aerial onto one of the bits of kit like the Radar or sounder then I would have two independent GPS systems without buying a complete second unit.
I have been looking at various aerials that just need a 12V supply and output NMEA 0183 but the cheapest and best one I have found I am usure from Garmins specs if it does what I want.
It is the garmin GPS 17HVS.
Can anybody confirm it does what I need or recommend a better one that can be pole mounted?
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Old 28 December 2007, 09:28   #2
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The Garmin 17HVS will do what you want.
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Old 28 December 2007, 10:18   #3
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Quote:
Originally Posted by BruceB View Post
I am running out of enough NMEA outputs to provide feeds to all the various electronics I have bought.
Bruce, are you aware that most units will drive at least 4 inputs from 1 output?
Rather than just having another antenna, why not buy a hand held GPS and use the output from this. If you stick with Garmin, you'll also be able to pass your routes and waypoints between the units and this will give you the flexibility to do trip planning whilst away from the boat.
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Old 28 December 2007, 10:56   #4
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I am not sure what you mean about driving multiple units from the one output. I have never had more than one from any one TX or RX but this doesn't mean it can't be done........
I have had two units conected from the garmin plotter I have and managed to drive the VHF and sounder off one channel by using TX and RX seperately. I was going to use the second full channel for the Radar.
I have actually ordered the second aerial because it means I can have a backup GPS without having yet another unit, probably linked into the Furuno NX300 navtex unit to give a display meaning it is completely seperate from all the other gizmos apart from power supply, and there will be two of them!
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Old 28 December 2007, 11:59   #5
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Each output from a unit will have a maximum number of inputs it can drive, this is called fanout and it is commonly 4 but it may be different for different makes of equipment. It will be dependent upon the interface chips within the units. You will do no harm by connecting more than the recommended number of units to an output. When there are too many, you will simply get an unreliable connection.
So, your main GPS/plotter can safely connect from one output (port) to your VHF, radar and navtex. Your VHF (if it can provide it) can connect to your main GPS/plotter on the same port to provide GMDSS data and your sounder can connect to the input of port 2 (if you have one) on the GPS/plotter to give depth information on the main screen if that is useful. This is the maximum number of inputs you can have since you can't normally connect more that one device to an input.

Other equipment you may have which requires an input can be connected to the output from port 2.

You can see that it is usually the input ports that limit you rather than the output ports.

Bear in mind, for your navtex to be truly useful it needs to be on all the time or, at least, a few days before you mean to use the boat.
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Old 28 December 2007, 15:00   #6
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I thought better of the Navtex and second aerial. I started to think that where am I going to fit 6 aerials where they don't interfere with each other on a sub 6m RIB!
VHF
Radar
AM/FM
GPS
2nd GPS
Navtex !
I have cancelled the active aerial and emailed to cancel the Navtex which cuts two out. I'll carry my handheld for backup and I have a AM/FM radio cassette being fitted for the shipping forecast!
That money would be better going towards an EPIRB or fitting out the electrical system of the console........
I have found dipole aerials for 4.99 that can be just round round inside the console, would this work OK on a marine AM/FM radio? It would save another aerial being frilled and mounted in the weather....
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Old 28 December 2007, 15:54   #7
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Bruce, is your handheld a Garmin unit and/or does it have an NMEA output socket?
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Old 28 December 2007, 15:59   #8
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It is a Garmin but has not NMEA output. I would use it with the laminated charts I carry for all my cruising areas to find my way home in an emergency.
I am not worried about intergrating it now into a second backup system as I realised I was going a bit over the top for the size of boat and where we operate. 90% of the time it would be pure pilotage with no reliance on instruments other than Mk1 eyeball!
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Old 28 December 2007, 16:09   #9
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Ok. I was going to suggest that you could simply wire it and your main GPS through a change over switch so if the main unit went down, you could move the switch and everything would be driven from the hand held unit. A wee project for the future.
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Old 28 December 2007, 17:14   #10
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All advice still welcome!
I hadn't realised I could drive more than one NMEA so this has tidied up the console and A frame........
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