Does anyone have experience with mounting two "mouse" GPS antennas in
close proximity of each other? Any interference issues? Specifically,
I'm thinking along the lines of two Garmin 35s, or a Garmin 35 and a
remote antenna for a Colibri, both within a few inches of each other
under an instrument panel cover.

Obviously if they are passive there shouldn't be a problem, but I see
the term "active antenna" used and I'm wondering...

Kirk

wrote:
> Does anyone have experience with mounting two "mouse" GPS antennas in
> close proximity of each other? Any interference issues? Specifically,
> I'm thinking along the lines of two Garmin 35s, or a Garmin 35 and a
> remote antenna for a Colibri, both within a few inches of each other
> under an instrument panel cover.
>
> Obviously if they are passive there shouldn't be a problem, but I see
> the term "active antenna" used and I'm wondering...

Indeed, placing two GPS receivers in close proximity to each other can
cause problems, due to radio frequency interference emitted by the GPS
receivers themselves. I've seen this most acutely with receivers from
two different manufacturers, place them within a few inches of each
other, and one or both will lose satellite lock in short order. I'd
keep the receivers separated by a least a foot or so (the GPS 35
receiver is, of course, inside the "antenna"). Placing the two antennas
in close proximity should be less of a problem, though I suppose RFI
from one receiver could in some cases leak into the other by way of the
antennas...

Marc

"Marc Ramsey" > wrote in message
m...
> wrote:
>> Does anyone have experience with mounting two "mouse" GPS antennas in
>> close proximity of each other? Any interference issues? Specifically,
>> I'm thinking along the lines of two Garmin 35s, or a Garmin 35 and a
>> remote antenna for a Colibri, both within a few inches of each other
>> under an instrument panel cover.
>>
>> Obviously if they are passive there shouldn't be a problem, but I see
>> the term "active antenna" used and I'm wondering...
>
> Indeed, placing two GPS receivers in close proximity to each other can
> cause problems, due to radio frequency interference emitted by the GPS
> receivers themselves. I've seen this most acutely with receivers from two
> different manufacturers, place them within a few inches of each other, and
> one or both will lose satellite lock in short order. I'd keep the
> receivers separated by a least a foot or so (the GPS 35 receiver is, of
> course, inside the "antenna"). Placing the two antennas in close
> proximity should be less of a problem, though I suppose RFI from one
> receiver could in some cases leak into the other by way of the antennas...
>
> Marc

I had a problem in my glider with a Garmin 12XL and my LX4000. The antenna
from the LX was mounted on a metal panel cover which when the canopy was
closed caused the loss of both signals to the GPSs. Had to fit a plastic
cover to cure this. The 12 XL is about 12 ins from the antenna of the
LX4000.

Peter.

Kirk,

As a data point, I am running a Cambridge 25 and a 302. The GPS
receivers are apporximately 8 inches apart their remote antennas about
10 inches apart.

I've seen no problems with any of my traces, nor have I lost signal
long enough to generate a message on my SN10.

OC

I run a 302 and a C M20. The antennae are about 6" apart. no problem at all
--
Hartley Falbaum


> wrote in message
ups.com...
> Kirk,
>
> As a data point, I am running a Cambridge 25 and a 302. The GPS
> receivers are apporximately 8 inches apart their remote antennas about
> 10 inches apart.
>
> I've seen no problems with any of my traces, nor have I lost signal
> long enough to generate a message on my SN10.
>
> OC
>

I have had my LX20 lose all lock when I turned on a Compact Flash GPS
in an iPaq. Both GPS' failed... only came back when I uncoiled the LX20
antenna wire, I had looped it up rathe rthan shorten the leads....
never coil the wire up in a ring I learned.

Bob

I have a gps patch antenna that went faulty, it was mounted in my car.
If powered it up it killed every GPS receivers reception within about a
100m radius. Great fun on the grid at the last Open Nationals.

Hmm, a low cost GPS jammer...very interesting!

Thanks everybody for the feedback & info; I'll have to make sure that I
test my installation thoroughly before flight. Which is a good idea
anyway!

Kirk

> wrote in message
ups.com...
> Does anyone have experience with mounting two "mouse" GPS antennas in
> close proximity of each other? Any interference issues? Specifically,
> I'm thinking along the lines of two Garmin 35s, or a Garmin 35 and a
> remote antenna for a Colibri, both within a few inches of each other
> under an instrument panel cover.
>

I've had problems with two GPS receivers near each other. My problem was
with a Garmin 12XL which wouldn't work on the dash of a specific car. I
eventually realised that the car was fitted with it's own GPS receiver under
the dash.

> Obviously if they are passive there shouldn't be a problem, but I see
> the term "active antenna" used and I'm wondering...


It's not just active antennas that will influence each other. I don't know
much about the technical stuff so can't offer a proper explanation, but
you've only got to look at a yagi type antenna (for example a TV antenna) to
see that mounting antenna near each other has an impact. Basically each
element in the antenna is an antenna in it's own right which receives and
re-radiates the signal. In a Yagi the purpose is to increase the
directional gain, but unintentional coupling of antennas is likely to have a
detrimental effect.

Stephen

After installing a microair transponder in my LS8 I recently found that
the 302 is losing the GPS signal. Both antennas were under the
instrument panel about 12" apart. Since I wanted to keep the
transponder antenna as far forward from my old body as possible, I
moved the Cambridge antenna back (had to splice the cable, the damned
thing has about a 10" length). All is well again with the GPS antenna
behind my head.
Slighly off topic but still interesting...

Herb, J7

wrote:
> Does anyone have experience with mounting two "mouse" GPS antennas in
> close proximity of each other? Any interference issues? Specifically,
> I'm thinking along the lines of two Garmin 35s, or a Garmin 35 and a
> remote antenna for a Colibri, both within a few inches of each other
> under an instrument panel cover.
>
> Obviously if they are passive there shouldn't be a problem, but I see
> the term "active antenna" used and I'm wondering...
>
> Kirk

Kirk,

I play with GPS for a living at Boeing, and you shouldn't see any
issues. Active antenna simply means there is an amplifier in the
antenna that boosts the output of the antenna, overcoming cable losses.

I'm trying to decide what sort of flight computer to buy - I'm ready to
discontinue the use of my L-Nav and GPS Nav. Any opinions?

Regards

Mark H.