Author: <gmcjetpilot@...> Time: Sun Jul 17, 2005 11:39 am PDT Link
Franz:
The opinions I express are my own based on my "design goals". As far as Archer antennas I think they are cool and heard Bob talk at Oshkosh many years ago. A very impressive back ground and unique ability to get these internal wing tip antennas to work at all. So much respect to Bob Archer but can't recommend an internal comm antenna in a metal airplane.
>From what you say it sounds like you are not flying yet. All I have to say is I personally have not used Bob's products, but familiar with it from friends, builder web sites and forums like this over the last 15 years. It appears you get different results , but many find that they just don't quite work well enough and produce annoying range limits and directional characteristics. They end up replacing it with a belly antenna. The other claims that it "works great" may be to justify their choice. The directional aspects of the antenna concept does not take a PhD in electromagnetic radio physics. Common sense would tell you a comm antenna stuffed into the tip of a metal airplane wing will cause many issues.
I mention my design goal. To me the Comm radio is one of those things you use all the time and is very important both operationally and for safety. You know ATC will ignore you if you are weak and scratchy radio. Worse is get them and than loose them. When getting flight following or Class B operations you must have a good comm with out major directional and range limits. Obviously if you can't talk to them at all it is a problem. Having a weak or directional Comm is a pain and will frustrate you a t best and at worst cause you some serious grief. Why mess with it? For an almost unmeasurable amount of speed? Hey it is just me, but I want to fly and use my plane and can't be bothered with comm issues.
If you want practical full power communications go with the belly antenna. If you just want to get ATIS or talk to ground or tower 5 miles out, than may be the internal antenna is all you need. Is this lower level of performance worth an extra 1/3 MPH? It is up to you.
I do know the Archer VOR/LOC/GS antenna does much better as it is receive only, but it does also suffer some directional issues as you would expect. However if you are going straight to it or from it, than it works OK.
I can't recommend any particular brand of bent whip. My guess is they are OK. I have bought two types/brands of bent whip VHF comm antennas before, both stainless and fiberglass. The Stainless whip looks a little more sleek (less drag?) but I recall was a little heavier than the fiberglass bent whip model. As far as transmission and dB gain, I don't know. You would need to go the an antenna test chamber (Electromagnetic Anechoic Chamber). I have a Dorne & Margolin DM C63-2, which is a nice looking unit. I also have used a Decibel Product Inc. VHF antenna, which is very high end pro brand, but can't find them any more. I am sure Comat is also fine. I don't know the differnece between a CI-122 or -291, but the -291 looks like a straight whip, which would not be as good as a the bent whip on the belly.
To me the bent whip on the belly is easy to install, not noticeable and performs very well. You can place it in the cockpit floor just fwd of the spar, to allow easy access to the BNC connector for a hand held radio if you desired as a back-up.
Cheers George
>From: "Franz Fux" <franz@lastfrontierheli.com>
>Subject: RE: VHF Comm Antenna
>
>Hi George,
>those are very interesting comments, considering that I did buy a Bob
>Archer wing tip antenna a while ago, the main reason being a clean outside
>surface. Looking at the antennas that Spruce has for sale, which one would you
>recommend, if any of them. The CI-122 or the CI-291.
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