Antenna

[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.