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Old 12-04-2014, 10:24 PM   #1
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How many GPS Antennas?

Thinking about reducing the mushroom farm on the top of the pilot house. Think I removed 5 or 6 antennas in preparation for painting. While some have specific purpose such as the satellite link for SIRRUS / XM, I think I have 3 that are tied to plotters or the nmea 2000 network. These are the older Garmin GPS 17 antennas with the slower position acquisition (1per second) rate. Was planning on upgrading to the faster GPS 19 antenna which acquisitions up to 10 times per second. Both plotters are tied to the nmea 2000 network, so I'm wondering why not just have one antenna on the network in stead of 2 or 3 tied to individual devices. Also, I have one antenna tied to a plotter and my Simrad AP20 pilot. This one outputs nmea 0183 at a slower rate. My plotter outputs nmea 0183, so I see no reason to to have a slower antenna just because it's tied to the pilot. That plotter can can give the pilot all the course and speed information it needs on its nmea 0183 port. See no reason to have a slower aquisition rate on that plotter. Does this sound reasonable, or am I missing something?

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Old 12-04-2014, 10:50 PM   #2
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Mushroom farm, that's hilarious. I have three - one for the plotter, one for the vhf radio (dsc) and one for the AIS transceiver. I would love to consolidate to one and I'm sure it could be done somehow, but I'd need an electronics degree and $900 in connectors and interfaces. The current setup is clearly not the most efficient but it is simple and direct (and I suppose the redundancy is worth something).
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Old 12-04-2014, 11:05 PM   #3
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Some of your antennas make sense, some to me at least do not.

Having a gps sensor with 0183 tied to your auto pilot in my opinion does not gain anything.

You could take the 0183 output from the plotter you use the most and have that feed your simrad autopilot. Then you would gain the ability to follow your course as opposed to heading mode only on the autopilot.

Having redundant gps antennas or sensors as the case may be is a good idea, if they back each other up.

For example I have a separate gps sensor tied to two of my Furuno Navnet VX2 displays. These displays will automatically generate an alarm if the primary sensor goes down but will output gps relevant data to all the devices on the network for redundancy.

Also a FYI, if you ever get a class b AIS they require their own GPS antenna.
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Old 12-05-2014, 07:02 AM   #4
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Interesting topic. We have 3 GPS antennas on the boat, and they are all hidden- no 'shrooms here!

2 are internal on the Raymarine e-125/127 units, and the 3rd is inside the lower helm console- it's feeding a Mac mini standalone nav system.. The autopilot is fed position info via the N2K network, and the DSC radio is on 0183.

Our Sirius sat antenna is a ow profile antenna used on cars; it's about 2" x 2" square, and sits on a platform centerline in front of the flybridge helm.
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Old 12-05-2014, 08:13 AM   #5
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Sounds like you are onto the solution yourself :-) Yes, redundancy is good, but if you think you have too many, you probably do. Moreover, if you have a solution... do it.

You can always keep a couple as back-ups, but they can be in a box under the stairs in case you need it.
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Old 12-05-2014, 08:18 AM   #6
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Quote:
Originally Posted by ksanders View Post
Some of your antennas make sense, some to me at least do not.



Having a gps sensor with 0183 ties to your plotter in my opinion does not gain anything.



You could take the 0183 output from the plotter you use the most and have that feed your simrad autopilot. Then you would gain the ability to follow your course as opposed to heading mode only on the autopilot.



Having redundant gps antennas or sensors as the case may be is a good idea, if they back each other up.



For example I have a separate gps sensor tied to two of my Furuno Navnet VX2 displays. These displays will automatically generate an alarm if the primary sensor goes down but will output gps relevant data to all the devices on the network for redundancy.



Also a FYI, if you ever get a class b AIS they require their own GPS antenna.

Couldn't have said it better. I just installed a 19x, and you can really tell the difference.
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Old 12-05-2014, 02:35 PM   #7
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Quote:
Originally Posted by O C Diver View Post

Both plotters are tied to the nmea 2000 network, so I'm wondering why not just have one antenna on the network in stead of 2 or 3 tied to individual devices.

If the single antenna goes south, none of the devices will have position info. While overkill isn't necessary, redundancy to a certain extent can be a good thing.

Ours are organized slightly differently; the plotter/GPS receiver has it's own GPS antenna, but our other GPS display -- without plotter -- is not on the same network and has it's own antenna.

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Old 12-05-2014, 02:50 PM   #8
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GPS antennas are a passive device. There are no moving parts. The most likely thing to cause failure in this neck of the woods is a lightning strike but the non metallic cover might provide protection from lightning. My preference would be to have as few GPS antennas as possible and keep a spare. But even then a lightning strike would most likely take out a lot more than the antenna.

How else might they fail?
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Old 12-05-2014, 03:51 PM   #9
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Most GPS antenna these days are active units. The "antenna" is actually a GPS unit with all the associated, complicated electronics.

The most common failure seems to be the depletion of the internal battery.

These days with the multitude of GPS chips that are in smartphones and even cameras it is hard to imagine being left with no functioning GPS unit ( it is worth putting one spare unit in faraday cage as protection against lightning).

However, at least two independent boat units that can be instantly switched are worthwhile, if possible.
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Old 12-05-2014, 04:17 PM   #10
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The Garmin GPS 19 antenna is NMEA 2K and gets power from the NMEA 2K bus. I guess it could need a battery for backup when the bus is off. I have always been confused as to what electronics are in the chartplotter and what is in the antenna.
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Old 12-05-2014, 04:48 PM   #11
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We are almost all nema 2000 now. we have 2 mushrooms on the same nema 2000 network. all devices have access to them, except the VHF which gets the data from the chartplotter. so one active and one for redundancy.
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Old 12-05-2014, 04:56 PM   #12
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I have always been confused as to what electronics are in the chartplotter and what is in the antenna.
Most of the GPS antennae these days are active units. That means they have all the electronics in the "antennae". It is a GPS unit, rather than a simple antennae as the older units were. The modern units usually get power via the data cable, but also typicallyhave a small battery that retains the satellite data when the unit is off.

A good clue is the cable connecting the antennae. If it has a coax cable it is a non active simple antennae. If it is a multi wire data cable it is a GPS receiver.

The internal battery in the active units seems to have a life around 5-7 years. It can be replaced, but you need to open the unit up and often do some soldering.

New units have very different chips to older models so I guess we will have to wait a few years to see if their reliability, or the need for battery replacment is different.
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Old 12-05-2014, 05:09 PM   #13
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I have one NEMA 2000 GPS on my Garmin network with three chart plotters. My AIS requires and has a separate GPS. My autopilot compass serves as a heading sensor and my autopilot gets navigation via NEMA 0183 from my Garmin Network.
I can't imagine why my autopilot would ever need its own GPS. Oh, I also have a GPS on my ships computer with OpenCptn. My back-up
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Old 12-05-2014, 05:11 PM   #14
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I have one GPS antenna on the radar mast that directly feeds the pilothouse Navnet and the 2 DSC VHF radios. The Navnet signal is output to the network hub where it is picked up by the PC Nobeltec navigation software and the second Navnet on the flybridge. As backup I have a GPS puck that connects via bluetooth to the PC/Nobeltec and to an iPad with Plan2Nav app. If they both fail, i have a Garmin handheld GPS that i use to mark the location of my crab traps.
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Old 12-05-2014, 05:28 PM   #15
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Raymarine had a huge percentage of the older Sea Talk antennas fail.

I was the go between warranty guy for a Sea Ray dealership with factory installed Raymarine equipment and the local marine electronics support company.

Can't say what was going wrong it was just a pull and replace operation under warranty.

Also some of the Furuno antennas failed quickly in about the same time frame 8 to 10 years ago.

If you have antennas of that vintage, having full time redundancy may be smart.
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