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Old 23-06-2016, 05:30   #1
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Installing an external Sat phone antenna

I am installing a GPS antenna for the AIS and a Sat phone antenna on the stern rail. I would like to run the cables together on the path I have identified to the nav station, about 40 feet. Is any separation of the antennas recommended on the stern rail and can the cables be zip tied together? Thanks.
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Old 23-06-2016, 14:54   #2
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Re: Installing an external Sat phone antenna

Calypso,
Two things to note here:
1) An AIS's GPS antenna is just that, a GPS antenna, which receives the L-band GPS signals (1575mhz and 1227mhz) and sends them down its coax to the GPS receiver built-in to the AIS transponder....
{note that is different than most other "GPS antennas" that we modern sailors use on-board, as these are typically GPS receivers built-in to the antennas, and then NMEA position data (or SeaTalk data, etc.) is sent down the multi-conductor wiring to displays, plotters, computers, autopilots, etc.)

2) Your "sat phone" also use the L-band....Iridium uses 1616mhz to 1626mhz....
Quote:
Originally Posted by Calypso52 View Post
I am installing a GPS antenna for the AIS and a Sat phone antenna on the stern rail. I would like to run the cables together on the path I have identified to the nav station, about 40 feet. Is any separation of the antennas recommended on the stern rail and can the cables be zip tied together? Thanks.
In theory, your AIS's GPS antenna could be placed close to your sat phone external antenna, and few (or no) problems should exist...also, the shielding of the two coaxial cables (the GPS antenna's coax and the sat phone antenna's coax) should provide sufficient isolation, so no interference of the GPS reception should occur...

But, in practice, in the real world....
I advise you to keep the AIS's GPS antenna at least a few feet away from your external sat phone antenna, and allow a few inches (or a couple feet) separation between the two coaxial cables....

There are of course satellite terminals with GPS antennas/receivers built-in to the same external housing as the satellite antenna....INMARSAT-C terminals have been this way for 20 years, with no issues....but they are specifically designed to do this, and must comply with all GMDSS standards (which your pleasure-craft AIS and "sat phone" do not!)
So...

So, my advice holds...


And, BTW...
There is usually no need to mount the AIS's GPS antenna outback on the stern rail....fiberglass boats / fiberglass decks, do not attenuate the GPS signals much, and you'll probably find excellent GPS signals from inside the cabin...
So, if you have a place near the cabin headliner / directly under the fiberglass deck (not under lots of metal), then try the GPS antenna there...




Fair winds..

John
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Old 23-06-2016, 16:54   #3
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Re: Installing an external Sat phone antenna

John, thanks for the detailed reply on this (and on all other topics electronic!) One follow up question if I may....

The 10 meter extension has been quoted at $150. Something about "it's not a regular 50 ohm SMA coax cable, it is a two way cable for sat phones...."

Appears I can get a 10 meter SMA coax cable on Amazon for $36. Should I save the $36 and get the proprietary cable?

Thanks again, Jonathan
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