GPS anetenna location OK in baggage area of a fiblerglass glider?

I'm doing a little housekeeping with instrument panel this winter with the intent to eventually install an ADS-B solution (whatever that may be). The panel is quite cluttered right now. I'm considering one option of moving the FLARM GPS antenna (and eventually a ADS-B GPS antenna) back behind my head somewhere in the baggage area. I'm curious if anyone has done this and has had any problem acquiring a GPS signal (on a fiberglass glider). I'm currently having no problems acquiring a signal with the GPS antenna under the fiberglass front panel. Thanks.

Hi Dirk,

My experience is that GPS antennas work fine through fiberglass and plastic.. The don't work well through metal or carbon fiber.

Best Regards,

Paul Remde
____________________

On Sunday, February 25, 2018 at 8:44:09 PM UTC-6, Dirk_PW wrote:
I'm doing a little housekeeping with instrument panel this winter with the intent to eventually install an ADS-B solution (whatever that may be). The panel is quite cluttered right now. I'm considering one option of moving the FLARM GPS antenna (and eventually a ADS-B GPS antenna) back behind my head somewhere in the baggage area. I'm curious if anyone has done this and has had any problem acquiring a GPS signal (on a fiberglass glider). I'm currently having no problems acquiring a signal with the GPS antenna under the fiberglass front panel. Thanks.

On Sunday, February 25, 2018 at 6:44:09 PM UTC-8, Dirk_PW wrote:
I'm doing a little housekeeping with instrument panel this winter with the intent to eventually install an ADS-B solution (whatever that may be). The panel is quite cluttered right now. I'm considering one option of moving the FLARM GPS antenna (and eventually a ADS-B GPS antenna) back behind my head somewhere in the baggage area. I'm curious if anyone has done this and has had any problem acquiring a GPS signal (on a fiberglass glider). I'm currently having no problems acquiring a signal with the GPS antenna under the fiberglass front panel. Thanks.

Many (most?) gliders, including carbon fuselage ones have a RF transparent area over the luggage space where you can mount GPS antennas if you want.

With the electronics mounted close by this is not usually an issue. But I'd avoid long runs of RF coax for an GPS antenna. You need to work out the lengths of all connections, power, data and any RF connections involved and what a reasonable maximum can be. Reducing space in the luggage area and putting stuff where it obstructs or can be damaged when rigging/inserting wing pins can be an issue. I'd personally do nothing that reduced available space there.

How many GPS antennas do you need? I'd be looking at keeping ADS-B antennas on a dedicated connection. Possibly combining other antennas though a RF splitter if absolutely required to save space.

The only reason the thought crossed my mind is because the stock FLARM GPS antenna wire is long enough to make the run, with distance to spare. In fact, I'm thinking about putting it BEHIND the luggage area (i.e. behind the spar) where it is completely out of the way (I didn't shorten the stock GPS antenna wire, but thought about it many times). Right now this is the only GPS antenna I have, but I will add an additional antenna for ADS-B at some point (maybe after the Reno show if anyone is offering any discounts - hint, hint for anyone listening). With just two antennas it doesn't make sense to try to put in splitter. Mounting will be the next issue. I was thinking about a couple of simple fiberglass cubby holes against the inside roof of the glider for the antennas to slide into (separate by some small distance).

Two questions;

Dirk_PW - What glider do you own? Do you know if it is fiberglass or carbon fiber? They all look the same on the outside, you know! As Paul says, fiberglass will allow GPS reception but carbon will not.

Darryl - I was unaware that "many" (!) CF gliders have this RF transparent area behind the pilot's head. That would be great as an optional area for mounting antennas as behind our panels things are getting pretty full these days. Any idea which brands/models have this feature? Schleicher ASW-27 by any chance?

PS - Darryl mentions concern about too long of a length of the coax on the GPS antenna. I would suspect, and hope, that the manufacturer wouldn't sell a GPS antenna with an overly long coax. The proof would be in the pudding I suppose - before you go to all the trouble of routing the coax fore to aft, test the functionality with all the coax laying out on the floor. BTW, shortening the tiny GPS coax, and fitting a new tiny connector to it, is much more difficult than a simple BNC.

Best of luck, John Ω

Thanks.

This may or may not be related, but...

I mentioned GPS dropouts to my avionics technician since I had several
GPS pucks under the fiberglass glare shield on my Stemme. They were
mounted directly under my Flarm antennae so I moved them to the top of
the glare shied and to the canopy frame up front. This took care of most
of the dropouts but there is still an occasional dropout.

The tech said he's seen this on power planes as well and he thinks it's
a failing GPS antenna.Â* He said that one antenna failing could
(apparently) transmit interference which could take out others.Â* He
suggested disconnecting my antennae one at a time and flying with that
system down and see if there are problems with the others.Â* It might be
less painful simply to get another GPS antenna (they're cheap) and swap
it around the cockpit from system to system and see if that fixes the
problem.Â* ...Or maybe an antenna combiner...

OBTW, there should be no problem with mounting an antenna underneath a
fiberglass cover.

On 2/25/2018 7:44 PM, Dirk_PW wrote:
I'm doing a little housekeeping with instrument panel this winter with the intent to eventually install an ADS-B solution (whatever that may be). The panel is quite cluttered right now. I'm considering one option of moving the FLARM GPS antenna (and eventually a ADS-B GPS antenna) back behind my head somewhere in the baggage area. I'm curious if anyone has done this and has had any problem acquiring a GPS signal (on a fiberglass glider). I'm currently having no problems acquiring a signal with the GPS antenna under the fiberglass front panel. Thanks.

--
Dan, 5J

It's not a problem to shorten the coax.Â* Simply open the antenna puck by
peeling off the sticker on the back and removing the screw(s).Â* The coax
cable is soldered conveniently in front of you and it's an easy thing to
remove it, cut and strip it to length, and solder back into place.Â*
Replace the cover and you're done.

Hmmmmmmm...Â* Regarding my previous post - maybe there's a problem with
my Flarm antenna since I shortened the coax.Â* I'll swap that one out
first as a test.

On 2/26/2018 6:59 AM, OHM Ω http://aviation.derosaweb.net wrote:
BTW, shortening the tiny GPS coax, and fitting a new tiny connector to it, is much more difficult than a simple BNC.

Best of luck, John Ω

Thanks.

--
Dan, 5J

maanantai 26. helmikuuta 2018 16.00.04 UTC+2 OHM Ω http://aviation.derosaweb.net kirjoitti:
I was unaware that "many" (!) CF gliders have this RF transparent area behind the pilot's head.

Well there is not, this is simply not true. Some level of satellite reception is possible trough canopy to that area. Only RF transparent area is usually at tail where VHF antenna is mounted.

On Monday, February 26, 2018 at 6:40:27 AM UTC-8, krasw wrote:
maanantai 26. helmikuuta 2018 16.00.04 UTC+2 OHM Ω http://aviation.derosaweb.net kirjoitti:
I was unaware that "many" (!) CF gliders have this RF transparent area behind the pilot's head.

Well there is not, this is simply not true. Some level of satellite reception is possible trough canopy to that area. Only RF transparent area is usually at tail where VHF antenna is mounted.

Every glider I've seen has white glass, not carbon, in the turtle deck. White glass is highly transparent to RF in that frequency range. You can check by putting a very strong light on the outside and see if the inside glows. It will through white glass, not through carbon. Sometimes it is covered with paint which makes it harder to tell (the light will penetrate the outside gel coat).

Within reason, you can have a pretty long coaxial cable on a normal GPS antenna. They have a 26 - 30 dB amplifier in them, so the signal from the antenna to the device is not weak. That is also the reason they can interfere with other GPS antennas and devices - if not well shielded and grounded, they become a transmitter themselves. Make sure if you shorten the cable at the antenna end that you get a good solder joint on the shield (easy to get a cold joint here because of the ground plane in the board). Another way to shorten the cable is to cut the other end and crimp on a new coaxial connector. The Flarm uses an MCX.

On Monday, February 26, 2018 at 6:40:27 AM UTC-8, krasw wrote:
maanantai 26. helmikuuta 2018 16.00.04 UTC+2 OHM Ω http://aviation.derosaweb.net kirjoitti:
I was unaware that "many" (!) CF gliders have this RF transparent area behind the pilot's head.

Well there is not, this is simply not true. Some level of satellite reception is possible trough canopy to that area. Only RF transparent area is usually at tail where VHF antenna is mounted.

I'm not sure which cereal box you are reading to get all your knowledge, but you might want to consider switching brands.