gps antenna placement

[Parfait's Provider]

The higher you place the GPS antenna the more it will move about and the less accurate it will be.

[SurryMark]

I just heard back from Garmin on their 17X antenna. They said, " Yes, the 17X antenna will work under the deck or inside a fiberglass locker in the cockpit..."

I don't know if it's worth spending another $180 or so for this unit, but there it is: if you really don't want to drill a hole in the fiberglass, you don't have to, although the idea of snaking the cable up through the engine vent or going through the dorade also does the trick.

[Steve Laume]

I snaked the wire down the stern vent just because it was easier at the time. I love to drill holes in my boat so that wasn't the issue. The wire has been a pain in the vent ever since!

It makes it hard to turn the vent around. When I went to install a bilge blower it made the job much harder than it had to be. If you ever want to put the plugs in for heavy weather you are just plain out of luck or stuck with stuffing a towel in the hole.

Putting a proper wire penetration in the aft deck is definitely on my to do list.

It will also mean that I get to drill one more hole in Raven. It always gives me so much reassurance to know just how heavy the layup is whenever I drill through it. The only place I don't want to add holes is below the water line, Steve.

[mexsailor]

I, too, went with the stern rail and clamp on base. Very easy install and it's always clear of any obstacles that might interfere with reception. A few years ago I went with a Lowrance 320 unit with a swing out mount. Works great! Love it...
mexsailor
CD25, "Gladys Erzella"
San Diego Bay

[Larry DeMers]

Do not use the top of the mast, or any part of the mast for your GPS antenna. GPS antenna require a location with a clear unobstructed view of the horizon..as good as you can make it anyway.

I personally know that the antenna needs to be at least 12 in. from any surrounding metal poles, or that sector of the sky will be blanked out.

Putting the antenna at the top of the mast works with VHF, since that is line of sight communications (or fairly close to that). GPS works at much higher frequencies, that are above the horizon, so there is nothing to gain from raising the antenna height, since a few 10's of feet make little difference when the satellite is 300 miles above us. Additionally, the swaying movement of the antenna will make it lose contact with satellites as it moves back and forth, screw up the speed calc, heading calc etc.

As many others commented, just mount it on the stern rail. It only weighs a few ounces, so no weight penalty. Give it a clear spot, away from the BBQ, stern anchor, stern ladder, outboard motor on the rail, radar pole etc. etc.etc. Heh..Paul's right. It is awfully busy on some boats (mine certainly).

Come On Spring!!

Larry DeMers
s/v DeLaMer
1983 CD30 #283
Lake Superior

[Duncan]

Hi Mark
I have a Garmin 400-series, which has an internal antenna. I did about 900 miles of sailing with it last summer, and there were no problems with signals.
On that basis, you might want to "keep it simple" and avoid the external antenna?

[sharkbait]

My Garmin took a big dump and when they replaced it they sent me a unit with an external antenna. I called Garmin and the next day received a replacement internal antenna. It just took a few minutes to install the internal antenna. You might consider doing the same thing. I to did over 900 miles (FL to TX) without any signal problems.

[Joe CD MS 300]

Mark,

It doesn't look like the 4208 chartplotter you were considering has an attached or internal antenna as an option. Depending on whether the fitting is the same you might be able to use one of the snap on swivel antennas used on some of their other units. For example my GPSMap 478 has one. I'm guessing they sell them separately. Mine works fine inside the pilot house and I have not noticed any difference in performance with the fixed mount 3006 chartplotter which uses an outside antenna.

Joe

[BarbofCapeCod]

Before you go to the trouble of mounting and having an external antenna anywhere, try your unit without one. We have a Garmin 454s, with no external antenna, swivel wall mounted within the main companion way.

Even with the hatch cover closed, dodger up, and mount swung inside the cabin, there is no problem with reception, with many satellites detected. When configured with a high refresh rate, it reports what seems like near instantaneous changes in speed.

[Leonard Lookner]

I believe that the instrument that we call an antenna is actually the GPS the other instrument that we view is a monitor.

[Joe CD MS 300]

Bill of Cape Code,

Did you mean 545s rather than 454s. Could not find that unit on Garmin's websirte. The 545s has an internal antenna with an external as an option. The 4208 that Mark was considering does not have an internal antenna, onlt an external option.

Joe

[BarbofCapeCod]

You are right. Must be my dyslexia, 454 should have been 545. If you have an external antenna, why not just leave it attached to or near the unit and see if it works okay that way.

I suggest this because we also own another boat, a Gaddy White Cuddy Cabin 20 and she has a Garmin (I dare to suggest 172c) GPS/Fishfinder with an external antenna (round hockey puck type), while the external antenna is attached, we keep it tucked in the stowaway storage area under a lot of other stuff and the GPS still works fine.

[Leonard Lookner]

Look I'm not an electrical wizard but once again I must correct you that the "hockey puck" is the GPS and the screen that you watch is a monitor or a computer. I have a Garmin GPS mounted on my stern rail that is wired to a connection strip in the nav station. I connected my VHF location feature and the USB wire to my computer plus I could connect another chart plotter monitor if I wished, all to the GPS(antenna).

[BarbofCapeCod]

Just to be sure we are referring to the same part. The "hockey puck" I am referring to is listed as:

"GA 29 remote GPS antenna (new design)
Part Number: 010-00174-03"

Displayed on the Garmin site at:

https://buy.garmin.com/shop/shop.do?pID=7650

Garmin's comment about this part is:

If you're mounting your GPS unit below deck, you'll need this remote marine antenna to receive GPS signals. Comes with 30 feet of cable and BNC connector. Can be mounted flush or pole.

This would seem to imply that the "GPS unit" contains an internal antenna, and the external antenna is only needed if the GPS unit is mounted "below decks".

My point, which I may have not made clearly and may not be relevant to you because of your other connection needs, is that GPS unit 545 with no external antenna seems to work fine when mounted below decks. Perhaps the limited mass of the CD28 does not limit the propagation of the signal enough to be of concern.

And perhaps any antenna, including one to suit your needs, might well function properly below decks as well.

[Joe CD MS 300]

Leonard,

I'm not quite sure what model you are referring to but I think Bill is correct. In general the "hockey puck" or "mushroom" looking components are the antennas. The guts of the GPS are in the unit that also includes the screen at least in most marine units including Garmin's. You can buy separate GPS units that are intended to attach to laptops. These separate units won't have screens but will contain the guts of the GPS electronics. All of the Garmin units mention in this thread are the types that integrate the screen and GPS "guts" into the same unit. Its just a question of whether they also include an internal antenna with the unit or whether an external antenna is either required or an option.

Joe