GPS antenna location

On Mon, 21 Jan 2008 09:51:04 -0800 (PST), Rob <skinner555.DeleteThis@comcast.net>
wrote:

>I have been getting conflicting advice about relative position in
>regard to my radar dome. Both will be mounted on my mast about 12 to
>24 inches apart. I have a choice of having the GPS right below the
>bottom of the dome or I could put an extension and have it extend a
>few inches above the dome. Any advice?
>Thanks
>Bob

Either is fine, as long as the GPS antenna is clearly outside of the
radar beam. (Although on a previous boat, an ancient GPS
antenna/receiver was mounted about a foot from a 4 KW radar scanner,
right in the beam, with no apparent problems.)


--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca
 >> Stay informed about: GPS antenna location 

On Mon, 21 Jan 2008 09:51:04 -0800 (PST), Rob <skinner555.RemoveThis@comcast.net>
wrote:

>I have been getting conflicting advice about relative position in
>regard to my radar dome. Both will be mounted on my mast about 12 to
>24 inches apart. I have a choice of having the GPS right below the
>bottom of the dome or I could put an extension and have it extend a
>few inches above the dome. Any advice?
>Thanks
>Bob

Disregard my previous post (although it is correct about keeping the
GPS antenna out of the radar beam). As others have said, the GPS
antenna should be mounted fairly low on the boat, and in a location
where it has a clear view of the sky in all directions.

Mounting the GPS antenna on the mast will cause it to see spurious
movements as the boat rocks. In addition, if the GPS antenna is
immediately below the radar scanner, the scanner will block the GPS
satellite signals from a fair portion of the sky.

--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca
 >> Stay informed about: GPS antenna location 

On Mon, 21 Jan 2008 09:51:04 -0800 (PST), Rob <skinner555.TakeThisOut@comcast.net>
wrote in
<a999739f-3fe0-4e5a-b019-94c67b451186.TakeThisOut@v67g2000hse.googlegroups.com>:

>I have been getting conflicting advice about relative position in
>regard to my radar dome. Both will be mounted on my mast about 12 to
>24 inches apart. I have a choice of having the GPS right below the
>bottom of the dome or I could put an extension and have it extend a
>few inches above the dome. Any advice?

Why put your GPS antenna way up there? GPS works well as long as it has
a clear view of the sky, and it's best to keep the cable run as short as
possible. I've not had any problems with antennas mounted on the stern
pulpit.

--
Best regards,
John Navas <http:/navasgroup.com>
 >> Stay informed about: GPS antenna location 

Rob wrote:
> I have been getting conflicting advice about relative position in
> regard to my radar dome. Both will be mounted on my mast about 12 to
> 24 inches apart. I have a choice of having the GPS right below the
> bottom of the dome or I could put an extension and have it extend a
> few inches above the dome. Any advice?
> Thanks
> BoB


Your mast will mask out quite a few of the satellites and make reception
difficult.

Set it on the pulpit rail away from any object that may prevent a view of
the whole sky.

The height is quite irrelevant for GPS reception.

Dennis.
 >> Stay informed about: GPS antenna location 

In article
<a999739f-3fe0-4e5a-b019-94c67b451186.RemoveThis@v67g2000hse.googlegroups.com>,
Rob <skinner555.RemoveThis@comcast.net> wrote:

> I have been getting conflicting advice about relative position in
> regard to my radar dome. Both will be mounted on my mast about 12 to
> 24 inches apart. I have a choice of having the GPS right below the
> bottom of the dome or I could put an extension and have it extend a
> few inches above the dome. Any advice?
> Thanks
> Bob

Well, since GPS and XBand Radar use different, and Widely separated,
frequencies, the only real, or apparent, problems should be the effect
of the RF Peak Pulse Output, of the Radar, mixing, or overloading in the
Frontend of the GPS's Antenna Mounted Preamp. This could be mitigated
by mounting the GPS Antenna Unit, outside the Radars, Vertical Antenna
Pattern, which is typically, Plus or Minus 12 degrees from the horizon.
Now, if you put the GPS Antenna, BELOW the Radar, the Radar itself will
block some reception from above, where is shades the GPS Antenna. If you
mount the GPS Antenna DIRECTLY above the Radar, No Problems. If you
mount it off to the side of the Radar, then you should position it, WELL
OUTSIDE the Radar Antennas Vertical Beamwidth, and more distance is
better, due to our old friend, Inverse Square Law.

--
Bruce in alaska
add <path> after <fast> to reply
 >> Stay informed about: GPS antenna location 

Rob, in article <a999739f-3fe0-4e5a-b019-94c67b451186
@v67g2000hse.googlegroups.com>, says...
>I have been getting conflicting advice about relative position in
>regard to my radar dome. Both will be mounted on my mast about 12 to
>24 inches apart. I have a choice of having the GPS right below the
>bottom of the dome or I could put an extension and have it extend a
>few inches above the dome. Any advice?

As others have said, mount it low down with a clear view of
the sky - and well away from the radar transmitter. A
friend's boat had one that was mounted above a radome that
wouldn't work when the radar was running. Apparently, the
cable going up to the GPS antenna routed in front of the radar
antenna wasn't a good idea...

Mounting it high up on a sailing boat also makes it subject to
position reporting error due to heel, not to mention confusing
it when rolling.

--
JohnW.
Replace the obvious with co.uk in 2 places to mail me.
 >> Stay informed about: GPS antenna location 

Is this a sailboat? I assumed powerboat with an electronics mast. If
it is sail, get it low and clear (as all the other posters suggested).
If power and you only have the mast space then separate as far apart
and I prefer BELOW the beam of the radar. I have 3 on my hardtop, all
mounted within 24" of an open array 4KW but all just below the beam. No
SNR issues at all.



Rob wrote:
> I have been getting conflicting advice about relative position in
> regard to my radar dome. Both will be mounted on my mast about 12 to
> 24 inches apart. I have a choice of having the GPS right below the
> bottom of the dome or I could put an extension and have it extend a
> few inches above the dome. Any advice?
> Thanks
> Bob
 >> Stay informed about: GPS antenna location 

> it's best to keep the cable run as short as possible.

Which is usless advice if it's a network-connected GPS antenna. NMEA2000,
SeaTalk, etc, are fine with longer cable runs.

You don't mention if this is a power or sail vessel.

Generally you want your GPS unit mounted where it's going to have an
unobstructed view of the sky. Putting it next to a radome might be a
problem in that the signal would be getting blocked. Not enough to entirely
lose all fix but enough to degrade the overall accuracy of it.

-Bill Kearney
 >> Stay informed about: GPS antenna location 

On Tue, 22 Jan 2008 00:24:09 -0500, "Bill Kearney"
<wkearney99 RemoveThis @hotmail.com> wrote in
<HeqdnRFYAOdm4AjanZ2dnUVZ_hudnZ2d RemoveThis @speakeasy.net>:

>> it's best to keep the cable run as short as possible.
>
>Which is usless advice if it's a network-connected GPS antenna. ...

And sound advice if it's a passive antenna, as is often used on smaller
boats.

--
Best regards,
John Navas <http:/navasgroup.com>
 >> Stay informed about: GPS antenna location 

Rob <skinner555.TakeThisOut@comcast.net> wrote in news:a999739f-3fe0-4e5a-b019-
94c67b451186.TakeThisOut@v67g2000hse.googlegroups.com:

> I have been getting conflicting advice about relative position in
> regard to my radar dome. Both will be mounted on my mast about 12 to
> 24 inches apart. I have a choice of having the GPS right below the
> bottom of the dome or I could put an extension and have it extend a
> few inches above the dome. Any advice?
> Thanks
> Bob
>

Wrong attitude. The GPS antenna has no need for ALTITUDE. Aboard
Lionheart, I got tired of them bumping into both the Raystar little dome
and the Garmin active antenna, so I mounted them INSIDE the overhead
cabinet in the galley, behind the helm (just forward of the bulkhead-
mounted wheel on an Amel 41 Sharki ketch). Fiberglass and plastic is
transparent to RF energy (especially RF tearing up the damned HF/SSB). The
signals work perfectly.

On a big center console fishing boat, they were looking for a good place to
mount the GPS so the fishing could tear it off and were looking way up
high, which is crazy. I said, "Let's just lay it INSIDE the overhead
cabinet behind the GPS and radios under the plastic bimini top and see how
it does across the harbor." During my free boat ride..(c;...we noted the
GPS worked perfectly with strong signals in all directions. So, when we
got back to the dock, having run completely out of beer, we mounted the GPS
antenna in the back corner of the INSIDE of that electronics cabinet, out
of the way of the other gear and wires. It's worked perfect there ever
since. If he had had a sheet metal top, of course, that wouldn't have been
possible. Noone fishing can get to the GPS antenna to rip it off, now.
They'll have to pull the overhead electronics console apart to even find
it!
 >> Stay informed about: GPS antenna location 

Always best to get the GPS antenna some distance from the radar and out of
the direct beam of the radar.

I agree that low down is generally ok. Mine is inside the fibreglass
flybridge with no apparent ill effects!

Alec


"Rob" <skinner555.RemoveThis@comcast.net> wrote in message
news:a999739f-3fe0-4e5a-b019-94c67b451186@v67g2000hse.googlegroups.com...
>I have been getting conflicting advice about relative position in
> regard to my radar dome. Both will be mounted on my mast about 12 to
> 24 inches apart. I have a choice of having the GPS right below the
> bottom of the dome or I could put an extension and have it extend a
> few inches above the dome. Any advice?
> Thanks
> Bob
 >> Stay informed about: GPS antenna location 

larry wrote:
> Rob <skinner555.DeleteThis@comcast.net> wrote in news:a999739f-3fe0-4e5a-b019-
> 94c67b451186.DeleteThis@v67g2000hse.googlegroups.com:
>
>> I have been getting conflicting advice about relative position in
>> regard to my radar dome. Both will be mounted on my mast about 12 to
>> 24 inches apart. I have a choice of having the GPS right below the
>> bottom of the dome or I could put an extension and have it extend a
>> few inches above the dome. Any advice?
>> Thanks
>> Bob
>>
>
> Wrong attitude. The GPS antenna has no need for ALTITUDE. Aboard
> Lionheart, I got tired of them bumping into both the Raystar little dome
> and the Garmin active antenna, so I mounted them INSIDE the overhead
> cabinet in the galley

Belowdecks is the way to go in a fiberglass boat.

My friend held the antenna alternately in the clear abovedecks, and
belowdecks hard up against the coachroof in various spots. I watched the
signal strength indicator on the chartplotter as she moved the antenna
between the abovedecks and belowdecks positions. In many spots
belowdecks there was no difference in signal strength from the
satellites with the antenna abovedecks or belowdecks.

My GPS antenna is now mounted in a good spot belowdecks, out of the
weather, away from running rigging and flying feet.
 >> Stay informed about: GPS antenna location 

Moonshadow wrote:
> larry wrote:
>> Rob <skinner555.TakeThisOut@comcast.net> wrote in news:a999739f-3fe0-4e5a-b019-
>> 94c67b451186.TakeThisOut@v67g2000hse.googlegroups.com:
>>
>>> I have been getting conflicting advice about relative position in
>>> regard to my radar dome. Both will be mounted on my mast about 12 to
>>> 24 inches apart. I have a choice of having the GPS right below the
>>> bottom of the dome or I could put an extension and have it extend a
>>> few inches above the dome. Any advice?
>
> Belowdecks is the way to go in a fiberglass boat.
>
> My friend held the antenna alternately in the clear abovedecks, and
> belowdecks hard up against the coachroof in various spots. I watched the
> signal strength indicator on the chartplotter as she moved the antenna
> between the abovedecks and belowdecks positions. In many spots
> belowdecks there was no difference in signal strength from the
> satellites with the antenna abovedecks or belowdecks.
>
> My GPS antenna is now mounted in a good spot belowdecks, out of the
> weather, away from running rigging and flying feet.

Better yet, get an internal antenna version of the unit, it
has optimal connectivity with no cabling. My Garmin GPSMAP
172C is mounted inside a pilothouse and always hits on any
satellite shown above the horizon, without problem.
 >> Stay informed about: GPS antenna location