More Antenna questions

[SCRed]

Thanks, Tom for the antenna question. I have and Advanced Aircraft Electronics antenna on my BC12D, the long thin ones that use no ground planes. And I have been having intermittent problems being heard for the last ten years. Now, I live in Southern CA and really need a working radio. Have new headsets, intercom, the best noise canceling microphones etc, and still the tower at Brackett and SoCal Approach say that I am barely readable. On the other hand, other places (Catalina Unicom) tell me that I am loud and clear.

I am now considering a whip antenna with a ground plane mounted outside the airplane. My questions are as follows.

1. I would like to place the antenna underneath the airplane. However, I have a Basic Aircraft wind powered generator mounted underneath just forward of the landing gear. Will this generator interfere with the operation of the antenna if the antenna is mounted behind it? And, any idea how far behind the generator the antenna should be placed?

2. There is already a bracket welded on the top of the plane where I can directly attach a whip antenna. If I do place the antenna on top of the plane, how much will the additional drag cost me in terms of airspeed?

3. If I decide to test a whip antenna before puncturing the fabric, will it work if it is attached to a ground plane inside feselage behind the baggage compartment?

[VictorBravo]

Re: More Antenna questions

I am now considering a whip antenna with a ground plane mounted outside the airplane. My questions are as follows.

In my experience the external whip antenna under the plane is the way to go. I also fly in SoCal, and have had plenty of problems with handhelds, old airplanes, and communications. As mentioned in another thread, I have a plywood plate and an aluminum ground plane, fixed to the floor tubes behind the baggage sack. The whip antenna is about 24-30 inches behind the landing gear bungees. the antenna has a 45 degree bend in it. It works extremely well, altohugh I have a good German panel mount radio instead of a handheld.

If you put the antenna on top of the airplane, the steel tube framework can be in between the antenna and the tower if you are (assumed) flying above the tower. The drag of the antenna above or below the plane should be negligible. You only need a very thin piece of solid wire, somewhere about 20-30 inches long if I recall (but the length is CRITICAL for "tuning" to the radio!!!). If you want to you can put a balsa or plastic sheet airfoil fairing around it and reduce the drag to a few ounces at 100 mph. The problem with the mounting tab on the steel tube is that the framework of the airplane will be a good ground, but perhaps not a good "ground plane" in radio terms.

I think it is a bad idea to have the antenna inside the steel tube frame, of course the frame would interfere with the signal! Mount your ground plane on the floor behind the seat, and have the antenna below the airplane.

The wind generator should not bother the antenna much if the antenna and radio is set up correctly. I have a metal prop that does not affect it so a smaller prop spinning should not either.

In many many cases it is not the radio or the antenna that is the problem, it's the wiring, the grounding, the coax cable, the connectors, etc.

The guy who set up the antenna and radio on my plane is available at a very reasonable cost if you are in need of some assistance. He has all the electrical test equipment, SWR signal meters, etc. to figure out very quickly where the problem is.

Bill

[SCRed]

Re: More Antenna questions

Thank you for the reply, Bill. I would very much appreciate the name and number of your radio man.

Lee Paulson

[selje]

Re: More Antenna questions

My antenna is a bent one on the metal boot cowl in front of the landing gear and works great with a handheld.

[JohnH]

Re: More Antenna questions

After removing the headliner I noticed this tab welded to the frame. Is this a antenna mount?

[VictorBravo]

Re: More Antenna questions

After removing the headliner I noticed this tab welded to the frame. Is this a antenna mount?

I believe so. It might work grounding the antenna to the frame, but Ik now there is alelgitimate reason for a "ground plane" in addition.

[Steve Green]

Re: More Antenna questions

I don't know for sure what the fitting in your picture is for, but when I got my plane that was where the switch for the navigation lights was located.

[Guest]

Re: More Antenna questions

...If you put the antenna on top of the airplane, the steel tube framework can be in between the antenna and the tower if you are (assumed) flying above the tower...

Bill

Mine is on top and what Bill decribed does happen when I am in the pattern. Unsually only when I am in the pattern though. Of course that's worse since you want to hear the tower good and fast in the pattern.

Otherwise it seems to work fine. I think if I remember it right the entire upper cabin section is the ground plane.

If was to do it over I am not sure what I would do. On the bottom it could hit weeds.

Dave

Dave

[Forrest Barber]

Re: More Antenna questions

I put it through the boot cowl with a round reinforcement plate. Antenna from Radio shack, trimmed back using a meter till we peaked the output, I used a Comm-Spec radio ( old critter) excellent noise rejection ( unshielded plugs) . i now have a NEW hand held Icom ; I will see how it works soon. On the other side of the lower boot cowl I had the Loran antenna, now GPS. Log book entry only.