Antenna

[Flybyjim]

I am at a point of deciding what antennas I need and where to put them along with the OAT probe. I am going to be using a G3X, GTX-45R transponder, GTR-200 panel mount radio. So the questions are, what have others used, the location of mounting and if flying how it all worked out.

[896tr]

Even though I had to sell my plane before I got it finished I made a vhf di-pole antenna and mounted it in the vertical stabilizer before I covered the plane. I had reports that even from inside my garage on a handheld it could be heard better than most of the other planes on the ground at the airpark that I lived at. Hell yes I was proud of that!:cool:

[jiott]

I have a bent whip radio antenna on the bottom of the fuse, RH side. The transponder antenna is on the bottom of the fuse, LH side. Both work very well. They are mounted on the two antenna mount plates that come standard on the SS7 fuse. My GPS antenna puck is mounted on the top side just behind the turtle deck. It also works great, looking up at the satellites in the sky. My ADS_B IN antenna is on the bottom of the fuse, in the center, just behind the stainless steel firewall piece that is bent back along the bottom.

Even though everything works fine where they are now, if I were to do it again I would mount the GPS puck inside, under the turtle deck, looking up. The comm antenna would go in the classic location on topside behind the turtle deck, and the ADS_B IN antenna would go on the bottom antenna pad, RH side.

[Flybyjim]

Thank you for the replies. Jim, you said you would change the locations, I am wondering why.

Personally, I was thinking about the comm antenna going on the top behind the turtle deck, transponder on the right side antenna tray and I was unsure about the GPS/ADSB in/out antennas. I have mounted the remote transponder beside the roll servo on the left antenna tray.

[PaulSS]

I am merely regurgitating what advice I've gleaned from reading various fora regarding antenna location but the learned opinion urges caution with the transponder and ADSB. Now, I know you chaps in the US have the UAT frequency and, therefore, this may be a moot point BUT if you're using 1090 MHz for the ADSB then you need to consider that this is the same frequency as the transponder and those beasties have quite a powerful transmission. Apparently we should ensure there's at least a 1/4 wavelength separation twixt the antennae but greater if possible. I'm not sure this presents any problems for the location as the wavelength is pretty short (0.275m) but it MAY be worth considering, lest your transponder totally swamps your ADSB receiver with its super powers.

As far as the type of antenna required, you can use the TED-type for both transponder and ADSB and they are pretty reasonably priced:

http://www.aircraftspruce.com/catalog/avpages/ted_transponder.php?clickkey=23156

[jrevens]

For what it’s worth, I welded on a mounting plate for my comm antenna between the turtledeck and the vertical fin. I bought the kit before the factory was putting their mounting plates directly behind the turtledeck along with the curved steel tube for the “razorback” look. So, my antenna is in a little different position than the new ones... not so close to the rear edge of the turtledeck. My “razorback” curve is therefore a little different also. My transponder antenna is on the belly mounting plate behind the passenger seat. My ADS-B antenna is on the bottom of a panel I mounted behind the baggage compartment, inside the fuselage structure. GPS antenna is front and center just under the instrument panel glareshield. Like PaulSS mentioned, the proximity of transponder and ADS-B antennas to each other is an important issue to some manufacturers. I’m not sure if the general consensus has changed with more field experience, but several of the available units that I checked out had strongly-worded warnings about maintaining minimum distances between the 2. In one case that minimum was 60”! Definitely something to check out and keep in mind.

[Esser]

Is the plate supplied adequate? I had a friend talk to me after I covered that I should have put a plate in the size of the antenna hieight squared...

[PaulSS]

To reduce to practical sizes, a ground plane in normally, again, based on 1/4 wavelength. For a transponder or ADSB monopole antenna, the ground plane radius needs to be a minimum of 2.6". So you can have a circular ground plane with that radius or a 5.2" x 5.2" square.

For the VHF radio it needs to bigger, since the frequency is a lot lower. Taking 118MHz as the lowest VHF frequency for our radios gives us a 1/4 wavelength of 23.8".

Of course, you don't actually need a square or circle of aluminium/some other metal. You can choose to 4 strips of metal or foil radiating out from the antenna. This might be useful for someone with a composite structure in which the antenna can be securely mounted. However, for fabric covered aircraft it is normal to use a 'complete' ground plane because it can then also be used to provide structure and strength to mount the aerial.

[jrevens]

Perhaps "antenna experts" can add clarity or correction to this, but here is my understanding in regards to metallic tube fuselage structures like our Kitfox designs... I have heard that a full 1/4 wave ground plane in the form of a disc or plate is not necessarily needed. Something much smaller, if properly attached and grounded to the fuselage structure seems to work very well, as per the experiences of a whole lot of builders/flyers. I've been told that the fuselage tubing/structure itself becomes an extended part of the ground plane, working very effectively in most cases... FWIW.

[jiott]

I am certainly no expert but have heard the same thing and agree with John, our steel tubing Kitfoxes don't need additional ground planes. None of my antennas (comm, transponder, ADS-B in, GPS, and ELT) have any additional ground planes other than the antenna mounting plates that come prewelded on the kit. I have been flying for 4.5 years now and everything works just fine. I won't argue that some additional ground plane MAY extend the range for a few miles, but I personally have never been dissatisfied with the range or clarity of any of my devices.

[efwd]

That is the info I got from the avionics guys at AS&S. I didn't add anything. Crossing fingers.
Eddie

[PaulSS]

I'm sure the guys at Kitfox have got a pretty good idea what they're doing ;)

I haven't seen the Kitfox mounting plates/ground planes (call them what you will) but, just for interest, this is the type used in the Eurofox (A220).

[Flybyjim]

Did you all remove the powder coating to get to bare metal when you mounted the antennas or did you rely on the mounting bolts to find ground?

John:: Did you make a tray to mount the gps antenna that is connected to the panel or use a clamp to one of the tubes?

I look at the photo section of the builds it seems most folks did not post much on the install of the avionics in their builds, they like to show the finished panel, I get that. I enjoy every part of the building process and as I look at where I prefer to mount items I find as I move along that perhaps that was not the best place as it now does/may interfere with something else down the road. Inventing the wheel is great but there are times I do not like doing things twice. Thanks for all the help and advice.

[PaulSS]

Hi Jim,

That is not my aircraft but a photograph of one when I visited the factory. However, I can confirm that the aerial body itself and the nut that secures it to the ground plane were definitely free of any paint or powder coating. In other words, the aerial was in direct contact with the mail to ensure a good ground.

[Esser]

Hey Jim. I think if everyone were to do their panels again they would mount things differently.

Basically just take everything you want and try to find what makes the most sense for you. You’ll add a couple things later that you forgot. I think most people don’t post where they put everything cause in their mind it’s not a perfect solution.

[PapuaPilot]

I have a G3X too. I put my antennas as follows:
-COM and ELT antennas on the top aft fuselage (my fuselage came with 2 mounting plates)
-ADSB in and transponder/ADSB out on the belly (3' apart)
-The small G3X GPS antenna (GA-26?) is under the glare sheild of the instrument panel. It plugs in the back of the GDU46 screen
-The GPS WAAS antenna for ADSB (GA-35) is under the turtle deck beneath the fabric of the baggage sack. I put a GPS-20 unit in that goes to my GTX-23ES transponder.

I put two 6" round aluminum ground planes with my transponder & ADSB in antennas (like the rectangle one already pictured). I grounded the disc to airframe ground and made sure the antenna ground made good contact with it too.

I kind of wish I had put the COM antenna inside the vertical stab. like other people have and my ELT antenna inside the tail. I hadn't found these suggestions until I had the fabric installed.

[Shadowrider]

I have a G3X too. I put my antennas as follows:
-COM and ELT antennas on the top aft fuselage (my fuselage came with 2 mounting plates)
-ADSB in and transponder/ADSB out on the belly (3' apart)
-The small G3X GPS antenna (GA-26?) is under the glare sheild of the instrument panel. It plugs in the back of the GDU46 screen
-The GPS WAAS antenna for ADSB (GA-35) is under the turtle deck beneath the fabric of the baggage sack. I put a GPS-20 unit in that goes to my GTX-23ES transponder.

I put two 6" round aluminum ground planes with my transponder & ADSB in antennas (like the rectangle one already pictured). I grounded the disc to airframe ground and made sure the antenna ground made good contact with it too.

I kind of wish I had put the COM antenna inside the vertical stab. like other people have and my ELT antenna inside the tail. I hadn't found these suggestions until I had the fabric installed.

Is there a thread on how to put your com antenna in the stab? That sounds like a good idea. I am just trying to get as many ideas as I can before I start building. Thanks

[jrevens]

...

John:: Did you make a tray to mount the gps antenna that is connected to the panel or use a clamp to one of the tubes...

Jim,
My “John’s Build”, post #192 shows the GPS mount. It’s just a simple mounting bracket attached to the tubing with 2 Adel clamps... there is no dedicated ground plane, nor is it needed. The antenna is mounted with Velcro.

[mr bill]

I put the comm and elt antennas in the vertical stab, making sure the antennas did not touch metal. They work very well. Transponder and ADSB antennas are on the bottom outside, under the baggage compartment.

[DesertFox4]

My project also has the comm antenna mounted in the vertical stabilizer.
It worked great in my model 4 for 13 years so figured I’d give it another go.
When I install the elt antenna, it will go inside fuselage next to the baggage compartment. Only external antenna is the blade transponder/adsb out antenna.
I installed the Apparreo transponder.