Mounting VHF antennas

[Kirk S]

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

[Mel]

Originally Posted by Kirk S

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

The problem with this is that you loose ground plane forward of the antennas. Will make them somewhat directional.

[Jpm757]

I have dual bent whips mounted aft of the spar right under pilot and copilot seats. No issues.

[gmcjetpilot]

The noisy (electrically) engine area is not ideal for antenna, along with SS firewall, engine, nose gear (as installed). More distance from these items would be better. You don't have a nice 360 degree ground plane around the base of antenna mounting near the firewall (as Mel said above). Also it's a dirty oily area in general.... With that said, if you want max clearance, mount it near firewall. Many have and it works... it's a compromise but up to you. All locations are a compromise one way or another...

Bent whip has plenty of clearance as said (for landing/TO/taxi on smooth surfaces). I think even a straight angled back VHF will work Tail dragger or Trike, but a bent whip will work. There are different bent whips. Get one that has the most vertical politicization. Bent whips where element that is parallel to fuselage is not ideal and will reduce your RX and TX range significantly. All locations and antennas are a compromise. You have to decide what is important.

Top of fuselage? You want clearance. With slider canopy you have to mount antenna a little further aft on fuselage.Longer coaxial so adds a little weight and minor loss in signal, but it will be more than be made up using a straight angled antenna with more vertical polarization (not bent) and an unobstructed location as you can get on an airplane with good ground plane. Up to you.

[BobTurner]

Originally Posted by gmcjetpilot

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!).

[PilotjohnS]

My general rule was to mount com 2 on top and com1 on bottom. Then use com2 for all ground communications because some people have had trouble with a bottom mounted antenna communicating with the tower while on the ground.

For me, I have a slider with the Supertracks. so my ELT antenna is going on top. This leaves little room for a top mounted comm antenna. So I am trying to figure out where to mount com2 besides next to comm 1 on the bottom.

JMHO

[RV7A Flyer]

Two bent whips on the bottom, aft of the spar, outboard bay of seat ribs. No issues whatsoever. Very rarely, like once a year or so, some Ground control at an airport will report weak and scratchy. Turning the airplane a couple of degrees (while taxiing or whatever) usually fixes it. I think it's the gear leg interfering.

Don't overthink it.

[BobTurner]

Originally Posted by PilotjohnS

So I am trying to figure out where to mount com2 besides next to comm 1 on the bottom.

JMHO

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!

[Walt]

My RV7A



Combination GPS/Com:

[az_gila]

Note that some airports, such as Tucson International (KTUS) require that you use a top mounted antenna for ground use.

As printed on the FAA airport chart here -

http://aeronav.faa.gov/d-tpp/2005/00430AD.PDF