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Old 26-09-2011, 17:32   #1
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Convert Internal Antenna to External

I have just replace my Garmin 492 chartplotter with a Garmin 4212. I would like to keep my 492 and mount it in my nav station as a back up, however, it has a internal antenna. Has anyone ever converted a chartplotter's internal antenna and made it external.

Bob
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Old 26-09-2011, 17:43   #2
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Re: Convert internal antenna to external

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Originally Posted by rnjpinz View Post
I have just replace my Garmin 492 chartplotter with a Garmin 4212. I would like to keep my 492 and mount it in my nav station as a back up, however, it has a internal antenna. Has anyone ever converted a chartplotter's internal antenna and made it external.

Bob
may work inside anyway...if not... any antenna that sends NEMA would work if the chartplotter can accept it and display it.
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Old 26-09-2011, 19:31   #3
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Re: Convert internal antenna to external

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may work inside anyway...if not... any antenna that sends NEMA would work if the chartplotter can accept it and display it.
Chances are that it will work inside with the built-in internal antenna. But if it doesn't, I don't think an external NMEA 0183 "antenna" will help. The reason is that the NMEA "antennas" are really complete GPS receivers that output standard GPS sentences. GPSMAP 492 outputs these sentences but it does not try to interpret them from external devices.
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Old 26-09-2011, 21:09   #4
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Re: Convert Internal Antenna to External

My Standard Horizon chartplotter and Garmin handheld both work fine inside the boat with internal antennas. Plastic doesn't block the signal, metal will and so will you. The Garmin 492 specs say internal or external antenna and the site lists external antennas as accessories.
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Old 27-09-2011, 04:17   #5
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Re: Convert internal antenna to external

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Originally Posted by Ziggy View Post
Chances are that it will work inside with the built-in internal antenna. But if it doesn't, I don't think an external NMEA 0183 "antenna" will help. The reason is that the NMEA "antennas" are really complete GPS receivers that output standard GPS sentences. GPSMAP 492 outputs these sentences but it does not try to interpret them from external devices.
Many chartplotters CAN accept NEMA and be switched to use that input rather than their internal antenna...at least hey did ten years ago when I was a tecnichian/installer of marine ekectronics.
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Old 27-09-2011, 05:01   #6
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Re: Convert internal antenna to external

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Many chartplotters CAN accept NEMA and be switched to use that input rather than their internal antenna...at least hey did ten years ago when I was a tecnichian/installer of marine ekectronics.
That is true for many chartplotters, but not the 492, according to the 492 manual (available here). Also it appears the 492 was sold in two versions, one with internal antenna and one with external. I don't think they included an external antenna connector on the internal antenna version.
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Old 27-09-2011, 05:04   #7
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Re: Convert Internal Antenna to External

The Garmin 492 is suitable for use with either internal or external antennas, like these.
https://buy.garmin.com/shop/shop.do?pID=369

See the Manual ➥ http://static.garmincdn.com/pumac/1068_OwnersManual.pdf
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Old 27-09-2011, 05:25   #8
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Re: Convert internal antenna to external

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Originally Posted by Ziggy View Post
That is true for many chartplotters, but not the 492, according to the 492 manual (available here). Also it appears the 492 was sold in two versions, one with internal antenna and one with external. I don't think they included an external antenna connector on the internal antenna version.
not an external connector but through the NEMA wiring..

You could be right as I didn't see anything n the manual/menu pages to switch to alt NEMA positioning but the fact it accepts DSC data...it just might...

when in doubt..call the factory!
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Old 27-09-2011, 05:44   #9
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Re: Convert Internal Antenna to External

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The Garmin 492 is suitable for use with either internal or external antennas,
There are two different versions of the 492. The one with an internal antenna does not have an external antenna jack and cannot be used with one.

Eric
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Old 27-09-2011, 05:53   #10
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Re: Convert Internal Antenna to External

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There are two different versions of the 492. The one with an internal antenna does not have an external antenna jack and cannot be used with one.
Eric
You and Ziggy are right. It won't be as easy as I suggested.
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Old 27-09-2011, 06:00   #11
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Re: Convert Internal Antenna to External -Solved!

A simple way to effectively achieve the same result as an external antenna if the internal one doesn't work satisfactorily is a GPS signal repeater as here:Pc-Mobile data cables audio adapters for PDA, GSM and GPS Bluetooth, Nikon PSP

Their shipping is quite reliable, and when there's no other simple way to solve the problem then $40 can seem cheap. Although it's battery (3xAA ) powered it's not hard to convert to 12 volt. Most phone car chargers can be used to give a 5v output cheaply.

The one I used gave a good signal anywhere within about 3 meters of the re-radiator, and the external antenna is waterproof -although I'd advise a little silicon on the back, and where the cable exits to make it fully 'marine'
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Old 27-09-2011, 06:15   #12
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Re: Convert Internal Antenna to External

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Originally Posted by fairbank56 View Post
There are two different versions of the 492. The one with an internal antenna does not have an external antenna jack and cannot be used with one.

Eric
do you know for a fact that it can't? NEMA input is through the data cable.... the question is will the intenal antenna model recognize and show NEMA GLL/etc sentences or only display GAMIN proprietary position info...as I said it will display DSC position info (at least the model in the posted above version)...so until the factory or someone who's tried this chimes in...all other comments about no antenna jack are kinda off track now...
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Old 27-09-2011, 06:28   #13
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Re: Convert Internal Antenna to External

The manual shows there is a way to configure the NMEA sentences for output, but doesn't show any input sentence selections. Given that NMEA input of fix data would probably be in conflict with the internal fix data...i.e. valid fix coming in through NMEA and invalid fix from internal data if the internal antenna isn't getting enough signal. Plus it's not normally the way GPS units are designed, they're designed to get their own fix data, not get it from NMEA input.

Bottomline? In the absence of positive contrary proof I'd guess NMEA fix data input from an external source won't work
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