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Author Topic:   GPS Antenna Positon
David Newman posted 04-29-2007 02:54 PM ET (US)   Profile for David Newman   Send Email to David Newman  
[Seeks the] best positon to locate a GPS antenna on a Montauk.
Chuck Tribolet posted 04-29-2007 03:03 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
On top of the console rail, unless you have a hardtop, then
on top of the hard top. Basically, you don't want anything
between the antenna and the sky, if possible. Even your hand
will substantially attenuate the signals.


dfmcintyre posted 04-29-2007 05:54 PM ET (US)     Profile for dfmcintyre  Send Email to dfmcintyre     
Try inside the console, as high up as you can. Alongside the flush mounted compass (if you've got a flush mounted compass)

Really, not a joke:

I had flush mounted my Garmin 135 and was, like you, trying to figure out where to mount the antenna. I had shock corded it to the grab rails around the windshield; up on the foredeck, etc. One day, after launching I noticed that the signal strength was only about 50%. Then realized that the antenna was laying inside on the floor of the console.

Hmm. I wedged it up between the front of the console and the compass (flushmount). I found that in that position I lose less than 10% of signal strength. Never lost a signal either.

Your mileage might vary, depending on wood thickness, gel coat etc.


DonD posted 05-09-2007 08:35 PM ET (US)     Profile for DonD  Send Email to DonD     
For me [the result obtained after moving the location of the GPS antenna] was night and day. The dealer originally mounted [the GPS antenna on my Boston Whaler MONTAUK] in the center, on top of the console, next to the compass, directly under the vertical piece of stainless [tubing which forms the hand railing around the console]. [The GPS] worked, but took forever to [acquire satellite signals]. After fooling around with [the GPS antenna] and living with [the long time necessary to acquire satellites] for about 6 months, I finally got fed up with [the long time necessary to acquire satellites] and temporarily mounted [the GPS antenna] on the top console rail, just to see if [the new location] would make a difference. Like I said, night and day. Huge improvement. Now [the GPS antenna is] permanently mounted there. I agree the less you have between [the GPS antenna] and the sky the better, but I never could see any difference between Bimini up or Bimini down. My GPS and SONAR is a Lowrance LMS-337C DF. I hope this helps. DonD
lurkynot posted 05-10-2007 12:26 PM ET (US)     Profile for lurkynot  Send Email to lurkynot     
I have the 18 Dauntless and the Garmin 498 w/ext antenna. Mounted it up on the console 1/4" away from the windscreen just starboard of center. From a cold start it aquires sattelites in about 15 seconds after the "I Agree" is depressed. From a warm start is virtually instantaneous. Best advice IMO is to try it running all electronics on whereever you intend mounting it before commiting the hardware. Had a boat years ago where the sonar when operating would interfere with the FM radio when both were on and Loran would act funny when transmitting with VHF radio.
bigjohn1 posted 05-10-2007 05:42 PM ET (US)     Profile for bigjohn1  Send Email to bigjohn1     
One size does NOT fit all in this situtation based on my experience and reading countless others'. Chuck is correct but it also depends to some degree on the quality of your GPS unit. If you buy low-end, expect low-end performance.
I spent a few extra dollars and bought high end I acquire satelites just as good with the antenna laying across my console as I do when its mounted atop the console grab rail. Also, bimini up or bimini down makes zero difference in my case.
jimh posted 05-10-2007 08:20 PM ET (US)     Profile for jimh  Send Email to jimh     
At the radio frequencies used in reception of the satellite signals for GPS receivers, the typical cloth such as Sunbrella used in a Bimini top appears to have very little attenuation. It also appears that fiberglass laminates such as those used by Boston Whaler in the molding of their center consoles do not have much attenuation for microwaves. Neither of these are very surprising results. Fiberglass laminates have often been used to form radomes over microwave antennas for decades.
highanddry posted 05-11-2007 03:39 AM ET (US)     Profile for highanddry  Send Email to highanddry     
My Humminbird can lock on while in the garage. The external antenna is surface mounted atop the console.
davej14 posted 05-11-2007 09:32 PM ET (US)     Profile for davej14  Send Email to davej14     
I went through this last year with a Dauntless console. I found there was a significant difference in signal strength between mounting to the top rail above the windshield and mounting below the windshield. I ended up mounting the antenna to the top rail.

Your GPS should have a mode that displays satellite signal strength. Trying various locations for yourself is the only way to determine the best mounting position for your specific situation.

highanddry posted 05-12-2007 12:40 AM ET (US)     Profile for highanddry  Send Email to highanddry     
My GPS signal inside the garage is rock solid. I have covered the antenna while in use with no loss of signal. I would day if you have a GPS that looses signal because of a bimini top or your hand or the Plexi wind screen you have a poor antenna and a poor system.
Chuck Tribolet posted 05-12-2007 06:03 AM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
I didn't say that your hand would make it loose the signal,
I said it would make it loose signal strength. I've seen
this on every GPS I've dealt with. The bars drop some when
you put your hand on top of the antenna. Those frequencies
don't go through much of anything.


highanddry posted 05-12-2007 11:58 AM ET (US)     Profile for highanddry  Send Email to highanddry     
My Magellon SportTrac works inside the house, my lap top with EarthMate works inside the car and inside the house, my Humminbird works iniside a three car garage, my Garmin Pilot III works inside the cockpit with the antenna on the unit and the unit attached to the yoke. The signal is attentuated but a good unit should still work just fine, if yours does not it is not a good unit.
davej14 posted 05-12-2007 03:36 PM ET (US)     Profile for davej14  Send Email to davej14     
Your geographic location and topography of your surroundings will also have an impact on available signal strength. While some antennas are undoubtedly better than others I would NOT make a blanket statement that if your GPS doesn't work inside your garage it is not a good unit. The high frequency low power signals of the GPS satellites are easily attenuated by line of sight obstructions. You need to test your specific unit in your actual application to determine the best mounting location.
Landlocked posted 05-21-2007 11:07 AM ET (US)     Profile for Landlocked  Send Email to Landlocked     
As I sit here writing this, I have a $4,500 Trimble GeoXT GPS sitting next to my office window trying to gather enough sattelites to acquire a fix. It cannot. It is, however; a very good unit capable of uncorrected measurements in the 3' accuracy range. With post processing, I have recorded measurements at known points within 1.5' of their actual location.


robbdrell posted 05-21-2007 01:54 PM ET (US)     Profile for robbdrell  Send Email to robbdrell     
i have an 18 dauntless with an older sitex gps and sonar. Both are a pain so i was going to go a combo unit and was looking at the Garmin 498 w/internal antenna. So these posts are very interestingto me. can i get away with a internal unit that i intend to mount in the console ? and how well does the does the sonar work? Mine loses the reading when i run and in shallow water. the transducer is transome mount. any thoughts are appreciated.



Chuck Tribolet posted 05-21-2007 08:43 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Even more than geographic location, what's your garage like?
What's the roof made of? How much stuff is stored in the
rafters over the boat?


davej14 posted 05-22-2007 08:03 AM ET (US)     Profile for davej14  Send Email to davej14     

I added a Lowrance sonar gps combo unit to my dauntless last year. I started with a unit that had an internal antenna but it had poor reception. I ended up taking it back and exchanging it for the identical model with an external antenna. I mounted the antenna to the top rail over my windshield and the performance is excellent. There was significant attenuation of the signal if the antenna was moved to the dash. This year Lowrance has different models and they have also changed their external antenna so the performance mat be different.I think that Garmin had a better antenna but I liked the look and feel of the Lowrance units.

How shallow is the water you have problems with and at what speed? I have had no problems with the Lowrance unit at any depth.

davej14 posted 05-22-2007 08:15 AM ET (US)     Profile for davej14  Send Email to davej14     

You may find the following link to a past discussion on this subject useful:

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