I am preparing to mount my vhf antennas on the belly right behind the firewall on an RV 7, have seem some right in front of the spar but I would like as much ground clearance as possible. Any know problems with this ?
TIA, Kirk S
Bent whips where element that is parallel to fuselage is not ideal and will reduce your RX and TX range significantly.
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So I am trying to figure out where to mount com2 besides next to comm 1 on the bottom.
JMHO
Bent whips where element that is parallel to fuselage is not ideal and will reduce your RX and TX range significantly.
I would quibble a bit about the word ‘significantly’. A bent whip which is bent in the middle (half vertical, half horizontal) will theoretically radiate 76% of its energy vertically polarized. In practice I’d say that’s not significant. Other factors are more important. On the ground, rebar in the concrete, landing gear, etc., can screw up the underside antenna’s ground plane (plus the tower is above the airplane) so a top antenna is better. But if flying high the bottom antenna may be better (a ‘perfect’ top mounted whip cannot communicate to the ground at all!).
One option is an Archer wingtip antenna. Properly installed, it?s still not as good as an external antenna, but not as bad as some seem to think (an unscientific test - because I used two different radios - I seem to get a useable atis on the wingtip at about 75% of the range for the same signal on the belly whip.). I use it for atis and backup, and works fine in that role. And one less external antenna, probably gains me 0.05 knots!
As far as I understand, the Archer wingtip antenna is for Nav (VOR) -- horizontal polarization.
Or is there also a vertical Archer? I can imagine that you could get partially vertical going from bottom of rib and up and out towards tip before you have to bend it horizontal.
Finn
I would quibble a bit about the word ‘significantly’. A bent whip which is bent in the middle (half vertical, half horizontal) will theoretically radiate 76% of its energy vertically polarized. In practice I’d say that’s not significant. Other factors are more important. On the ground, rebar in the concrete, landing gear, etc., can screw up the underside antenna’s ground plane (plus the tower is above the airplane) so a top antenna is better. But if flying high the bottom antenna may be better (a ‘perfect’ top mounted whip cannot communicate to the ground at all!).
I ham radio guy. I agree. It is not practically significant. It is however something, polarization does matter. Not to drive into the weeds, RF has an electrical field and magnetic field (electromagnetic field). Polarization matches the electrical field. The orientation of element of the antenna is the polarization. Matching the polarization of the RF antenna of incoming signal gets maximum signal. If the RF antenna polarization does not match there is a loss by the factor of cosine of the angle between the polarization of the RF antenna and the signal. Theoretically it could be ZERO! However there is no pure polarization but antennas can have deep nulls and be directional. Often RF signals bounce around and polarization is mixed. Usually a VHF line of sight signal does not change much unless it bounces off objects. We are rocking the unbalanced dipole in a metal airplane. At 12,000 feet you might get 100 miles with 10 watts and a coat hanger in your mouth. Ha ha. (don't try it)I have had conversations with other planes that were over 100 miles away, now much degradation could there be?
As for placement, I put the antenna under the pilot's seat, just forward of the spar. In fact, the aft two machine screws for the antenna go through the spar flange and the front two are secured to platenuts on doubler. I am thinking of adding a second radio and will put it on the other side and mount it the same way. That way you don't have to run those thick cables through the spar, which as you know has limited space to pass wires through.
(click to enlarge)
I did a similar thing in my old RV-4. Great location.Bill R.