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

On Mon, 21 Jan 2008 09:51:04 -0800 (PST), Rob
wrote in
:

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

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

On Tue, 22 Jan 2008 00:24:09 -0500, "Bill Kearney"
wrote in
:

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

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.

In article
,
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

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

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

I put mine on top of the stern arch and that's a mistake. Once in a
while I get some reading of 50 knots or more. I think they are caused by
the rocking or rolling of the boat. I would put the antenna as low as
possible near the center of motion that has a clear view of the sky. You
know there is a place on the boat that actually doesn't move. Put it
there. :-)

Jeannette

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.

On Mon, 21 Jan 2008 19:52:29 -0000, JohnW
wrote:

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.

I was under the impression that GPS results are referenced to the
location of the antenna. So what does heel have to do with it?

Casady

Richard Casady, in article 47b6d18e.1524399671
@news.east.earthlink.net, says...

I was under the impression that GPS results are referenced to the
location of the antenna. So what does heel have to do with it?

When you are heeled over, the antenna, if up the mast, will be
over to the side somewhere, some distance from the boat
centerline where it will be giving an incorrect position
report for the boat. Since heel isn't constant, the error
introduced by heel would be variable.

Not that you should be using the position information reported
by GPS to that level of accuracy anyway :-) However, there
have been several GPS assisted collisions with fixed landscape
features, so perhaps that isn't true anymore?

If you are pitching and rolling, the antenna will be moving
relative to the boat so the GPS will include that motion in
with the boat's forward velocity in its speed calculation.
---
One problem with mounting the antenna at deck level, under the
pushpit, is that from a dinghy, it looks too much like a
handle to help getting on deck. If on the pushpit, it can get
knocked. I have mine under the GPS structure which has no
reported signal strength implications. It also isn't a
visible "I've got a GPS available for stealing" signal...

--
JohnW.
Replace the obvious with co.uk in 2 places to mail me.