GPS Antenna Location

Hi Folks,

Does anyone out there know if there are any adverse
effects of mounting two or more GPS antennae in close
proximity?

I'd like to fit two (maybe 3 !!! ) antennae (Colibri
/ EW type 'Radomes') on the instrument panel coaming
of my Discus. Is this likely to cause any problems
in acquiring or tracking the GPS position?

Thanks

Kevin

Kevin,

I have found that the antennas interfer with eachother and you may not
get GPS locks on one or both.

I once mounted a CAI 302 Active antenna and a Colibri active antenna
next to eachother. The Colibri would not lock. I move the antennas
about 2' apart and all worked OK.

Richard
www.craggyaero.com




Kevin Neave wrote:
Hi Folks,

Does anyone out there know if there are any adverse
effects of mounting two or more GPS antennae in close
proximity?

I'd like to fit two (maybe 3 !!! ) antennae (Colibri
/ EW type 'Radomes') on the instrument panel coaming
of my Discus. Is this likely to cause any problems
in acquiring or tracking the GPS position?

Thanks

Kevin

Kevin Neave schrieb:

Hi Folks,

Does anyone out there know if there are any adverse
effects of mounting two or more GPS antennae in close
proximity?

I'd like to fit two (maybe 3 !!! ) antennae (Colibri
/ EW type 'Radomes') on the instrument panel coaming
of my Discus. Is this likely to cause any problems
in acquiring or tracking the GPS position?

Thanks

Kevin

Most providers of GPS equippment recommend a distance between antennas
of at least 25cm. All nonsense.

A friend of mine experienced interference at distances greater than 1
meter: The FLARM antenna fell off from where he had taped it and was
dangling by the feet. Over the next few minutes first the LX5000, then
the first LX20 with antenna on the old camera mount and then the second
(!) LX20 located in front of the main spar lost satellite reception.

On the other hand I have seen setups with two antennas stuck together
under the panel working for years with no problem.

There's only one way to go: You have to try it and if it works you're
lucky and else you have to move one of the antennas. As has been
mentioned moving an inch or two can make the difference.

Regards
Marcel

Kevin Neave wrote:

Hi Folks,

Does anyone out there know if there are any adverse
effects of mounting two or more GPS antennae in close
proximity?


Yes, if the antennas are within (roughly) one wavelength,
there can be interference. That would be 20cm or so.

It depends very much on the antennas (patch/helix, active/passive)
and on the receiver itself.

In general, active antennas will be better neighbors.
However, I have once encountered a GPS antenna which
started to oscillate when it got cold and effectively
jammed 8 other antennas within a meter radius.

Unless you want more than one antenna for redundancy, the
classic way to handle this is to use a single high-gain
active antenna and a RF power splitter.

For example, the device at th bottom of this page:
http://www.procom-dk.com/component/d...ower-splitters

An active antenna needs power, which is normally fed
into the cable by the GPS receiver.

If you use a power splitter, make sure only one receiver
feeds power into the antenna. This is called "DC feedtrough".
Some power splitters have it on one port only, others
(like the one in the link) does it on all ports. In that case,
you need "DC blockers" on all but one port.

As you will notice, the splitters are not cheap.

I would advise to try placing the three antennas as far
apart as possible on top of your panel and see what
happens. As long as you are aware of the potential
problems, you can always switch some of the instruments
of when you get "bad reception".

Kind regards,

Iwo

"Kevin Neave" wrote in message
...
Hi Folks,

Does anyone out there know if there are any adverse
effects of mounting two or more GPS antennae in close
proximity?

I'd like to fit two (maybe 3 !!! ) antennae (Colibri
/ EW type 'Radomes') on the instrument panel coaming
of my Discus. Is this likely to cause any problems
in acquiring or tracking the GPS position?

Thanks

Kevin




You might instead try using a satelite TV signal splitter (2 GHz) to allow
two devices to share an attenna. This has worked perfectly for me.

Iwo Mergler wrote:
Kevin Neave wrote:

Hi Folks,

Does anyone out there know if there are any adverse
effects of mounting two or more GPS antennae in close
proximity?


Yes, if the antennas are within (roughly) one wavelength,
there can be interference. That would be 20cm or so.

It depends very much on the antennas (patch/helix, active/passive)
and on the receiver itself.

In general, active antennas will be better neighbors.
However, I have once encountered a GPS antenna which
started to oscillate when it got cold and effectively
jammed 8 other antennas within a meter radius.

Unless you want more than one antenna for redundancy, the
classic way to handle this is to use a single high-gain
active antenna and a RF power splitter.

For example, the device at th bottom of this page:
http://www.procom-dk.com/component/d...ower-splitters
into the cable by the GPS receiver.

Is there a device that allows two aircraft transceivers to use one antenna?


--
Eric Greenwell - Washington State, USA
Change "netto" to "net" to email me directly

"Transponders in Sailplanes" on the Soaring Safety Foundation website
www.soaringsafety.org/prevention/articles.html

"A Guide to Self-launching Sailplane Operation" at www.motorglider.org

Is there a device that allows two aircraft transceivers to use one antenna?

Maybe or more accurately, there could be. Hybrid combiners are used
regularly to allow 2, 4 or even more transmitters to work into one antenna.
Many tower owners require them, because it increases revenue.

They are not cheap and it would be much cheaper to have two separate
antennas rather than using a combiner. They would need to be designed and
built for the aircraft band and I do not know if any are actually sold.
They also would weigh more than the second antenna.

The combiners I am familiar with are called Hybrid Ring Combiners. The one
I used was working at 100 watts input.

Colin Lamb