Best location for antennas?

M

madrob

New member
Hi all,

I would like to hear opinions on where the best locations for COM and ELT antennas are and what mounting methods were used.

I am close to doing the fabric on the fuselage on my 1958 7GCA restoration and want to make sure I get everything sorted out before I cover it.

I am considering mounting the COM antenna on the belly of the boot cowl so it's close to the radio and out of the way. The plane used to have the COM antenna mounted on the topside of the wing root gap strip but I want to keep away from this since I think it's a great way to get water in the airframe. I have done enough repair due to water infiltration!

I saw a new GCBC at a fly-in this spring and noticed that it had what looks like the com antenna mounted on the topside of the fuselage about halfway between the wing and tail. I assume this is secured to a plate running between the two top wooden stringers?

I was also thinking of mounting the ELT antenna on the belly aft of the baggage area. I would run an Al plate between the two wooden belly stringers and secure the ELT antenna to this. My ELT is located just aft of the baggage area.

Thanks for any opinions!

Rob

PS I just bought a transponder so need a location for that antenna as well!
 
Rob-

The belly isn't a good choice in this aircraft because you will operate into grass strips. The current factory antenna is placed in the middle of a sheet of aluminum that, in conjunction with copper wires arranged in a radial fashion, acts as the required ground plane.

Antenna placement, and performance, is a problem with fabric covered aircraft due to the lack of a good ground plane.

I would suggest you consider using the ribbon antenna from, http://www.advancedaircraft.com/ While I have no personal experience with it I have heard good reports from it's use in other fabric covered aircraft.

Tom-
 
Thanks Tom,

I have considered the ribbon antenna but I have not been able to find room for it. I'll do some more exploring and see if I can find a good location.

BTY: I remember an article on one of Bill Pancake's Champs that showed an antenna on the belly of the boot cowl. I think you would have to be in grass over 1 ft high to make contact with the antenna. I would rather replace the antenna every 5 years due to stone chip dammage then have holes on top of the airframe. I'm a little paranoid about water getting in after having to replace a tube, both rear window frames and the wood cieling structure all due to water dammage.

Cheers!

Rob
 
I have reports that the Advanced Antennas are poor from an efficiency standpoint. That little black box in the center is a ferrite transformer and the very best of them burn up at least 2db of signal (about 25%). I don't think you should throw away perfectly good signal. Someone (trying to find the report) did a direct comparison between it and the (Bob Archer) Sportcraft Antenna and he bought the Sportcraft. And it was cheaper.
 
My '58 7FC/EC has the following setup:

Comm antenna is - and I know you don't like this - on the top left wing-root fairing. A piece of .040 aluminum was added to the back side as a stiffener. The antenna has a cork & rubber gasket. A little extra silicone or something should keep the water out. Mine is hangared so I don't fret it. Several people have commented on how good my radio sounds, so I guess it works well. I have a Bendix-King KY-97A (I think; comm only, 12 volt).

ELT antenna is inside the structure. I welded a tab to one of the near-vertical tubes on the left side. It's just behind the baggage bin. The cable runs through the same tunnel as the elevator cables and the ELT itself is on the left floor behind the rear seat. In my (not so) humble opinion the ELT is good for one thing - satisfying the feds. I won't count on it to save me. It might be good for locating my remains, though...

Transponder antenna is under the boot cowl, just ahead of the axle strut plate in the center of the fuselage. The cable runs down the fuel line between the valve and gascolator, then through the floorboard to the antenna. This also has a doubler plate riveted to the cowl. It's just off center to avoid the overlapped area.

Jon B.
 
I discussed this with Bob Archer of Sportcraft (he flies a Cruisair), there is no way to use a small or internal antenna with a steel cage airframe. Neither the Advanced, nor his Sportcraft can take the place of a good ground plane external antenna. Most problems are in the installation; check for a proper ground plane, double-check the connections, cleaning them occasionally, especially in marine locations.

The Sportcraft, however, are excellent in composite and sheet metal airframes; there is a virtual run on them from RV builders.
 
Thanks for the responses guys!

I think that I will mount the com antenna on the underside of the boot cowl. I'll use one that has a bend in it. I will mount the transponder antenna on the belly under the baggage area. I'll have to make a backing plate to mount under the fabric skin but this should be no problem.


I will mount the ELT entenna internally, aft of the baggage compartment like Jon B. has in his plane.

I do not have a hanger now so she will probably spend a summer or two outside until I can afford to build one. I want the topside clear so I can use one of the nice cabin/wingroot covers and a topside antenna would complicate things.

Now I just have to figure out how to fit all this stuff in the panel. It was already pretty crowded before and now I'm adding a transponder, intercom and a EGT guage. I don't want to resort to using a Citabria panel as the Champ one looks so nice.

Cheers!

Rob
 
Hey Rob:

I can send a photo of my panel, it you'd like. I got a blank from Safe-Air and punched & drilled it myself. If I do say so, it looks pretty nice. I have a comm radio, transponder, remote for the ELT, ASI, ALt., tach, oil pressure, oil temp, generator idiot light, cabin heat, mixture (inop), intercomm, and wet compass all installed in the panel. The primer and starter hang below, on the bottom cross-tube.

Oh, yeah, there's still room for the fancy chrome "Champion" logo.

I'll see if I can scrounge a photo from the rebuild. I have some of the ELT installation, too.

jbar@rice-willmar-mn-us Replace the " - " with periods.


Jon
 
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