Can You Hear Me Now? by Amit Dagan
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One question which seems to come up time after time, concerns the placement of the VHF comm antenna on the airframe. Many factors need to be addressed when deciding on the final spot for this important part of the radio system:
1. Is the proposed mounting spot strong enough (structurally) to support the antenna, in the 200+ mph wind it will endure?
2. Will a long run of coaxial cable to a wingtip (and the weight penalty) be worth it for the savings in drag – the promise of an in-the-wingtip installation?
3. Is the placement going to hurt the transmit/receive performance of the radio, because of electronic “shadowing” by other structures (e.g. – gear legs)?
4. Is the proposed mounting spot conducive for easy maintenance?
And another issue to think about:
5. Will it be possible to easily hook up a handheld transceiver to this antenna in the event of a comm radio failure?
I believe I have read somewhere that for the RVs, the best place for a comm antenna, as far as the transmission and reception is concerned, is the top of the vertical stabilizer. Indeed, if you have enough room under the fiberglass fairing on top of the vert. stab, you might benefit from placing your antenna right there. Your weight penalty of running a coax all the way from your instrument panel to the tail is another matter to consider.
I suspect that the small penalty in drag of having the antenna mounted on the belly is worth the saving of the coax run. The skin right in front of the spar carry-through is thick and reinforced by the spar angles and floor stiffeners. Further more, by placing the antenna in the position shown in the picture, it is easy to reach down between your legs, disconnect the BNC connector, and quickly attach a handheld transceiver with a 3’-4’ length of coax.
Belly mount. View from pilot’s left ankle. View from pilot’s left knee.
So, can you hear me now?
Amit Dagan [amitdagan 'at' comcast.net]