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Dorsal comm antenna?

GyroF-16

GyroF-16

Well Known Member
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Has anyone tried mounting a comm antenna between the canopy and vertical stabilizer on an RV-4 / 8 / Rocket?

I’m adding a second comm radio to my F1 Rocket, and the local avionics shop seems to think that a dorsal mount would work.

There is some room between the canopy track and the rudder, even allowing room for removing the horizontal stabilizer fairing.

It would certainly be an advantage to have the antenna much farther from the belly antenna for the other radio. And much shorter coax runs to the remote-mounted radio in the aft fuselage.

My concern is how close the antenna would be to the vertical stabilizer, and how that would affect the function of the antenna.

Anyone have experience with an arrangement like that?
 
When you take the canopy off the RV-8 it slides all the way back to very nearly touching the vertical stab. Depending on the size and shape of the skirt.
So you would have to remove the antenna to take the canopy off.
 
For the RV-8 the short answer is no, this will not work.

I have two bent whips on the belly mounted under the rear passenger foot wells, one on each side. No interaction noted.

Carl
 

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Got a mate with the same arrangement, he reports no issues. Am putting mine in the same place.
 
Jonnyb said:
Got a mate with the same arrangement, he reports no issues. Am putting mine in the same place.
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Your mate has 2 x belly mounted antennas, I take it?

For perspective, my Rocket had this much room on the aft fuselage with the canopy fully open.
I guess it’s significantly different from an RV-8 in that way.
IMG_0312.jpeg
 
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Probably a dumb question, but is the difference in room available between the canopy and vertical stabilizer between the RV-8 and F1 pictures based on normal slider vs fastback, and if so would an RV-8 fastback also have more room there?
 
I placed one on top of the vertical stab. Works fine out to 20 miles. Primary is under the wing.
 

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STARGATE said:
Probably a dumb question, but is the difference in room available between the canopy and vertical stabilizer between the RV-8 and F1 pictures based on normal slider vs fastback, and if so would an RV-8 fastback also have more room there?
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A standard RV8 fastback folds over on opening. So the entire turtle deck is available space. Here is a pic of my fastback with the canopy in the taxi position.

IMG_4633.jpeg
 
Need to find someone willing to make a composite vertical tail component. With that we could install a vertical antenna inside, possibly two. I used a diapole com antenna vertical inside on one of the winglets of a Long EZ. Seem to work quite well imbeded in the composite structure.
 
Hey Pete - don’t overthink it, and ask your avionics shop how many installations they have done on Rockets…. 😉

Three of our RV-type airplanes (-3, -6, and the F1) have two comm antennas on the belly and they work just fine. The -8 (which I built over twenty years ago and had concern over antennas being too close to each other) has one centered belly antenna and an Archer in the wingtip. The Archer is good for AWOS from ten miles and formation work - otherwise its a wasted radio (that I just never get around to fixing…). One belly antenna under each side of the pilot’s seat (or under the passenger footwells, which is the same thing) works well, is easy to do, has short wire runs, and IMHO looks better than an antenna sticking up where it doesn’t need to be. Unless you like the looks of it in front of the Vertical Stab, and then go with what YOU want (not the avionics shop).
 
Walt said:
Two words: Ground Plane
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An antenna mounted on the top of the HS is a hybrid, but I’d guess the better model would be a vertically mounted half wave dipole as compared to a quarter wavelength antenna over a ground plane.

Ironflight said:
The Archer is good for AWOS from ten miles and formation work - otherwise its a wasted radio (that I just never get around to fixing…).
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It is possible to make a wingtip comm antenna (along the lines of the commercial Archer antenna) work well enough to be a viable Comm #2 antenna. This requires modifying the design to use all the availble space in the wingtip and to carefully fabricate it so that as much of arm extending out from the wingtip is angled either up or down. The first third or so of the antenna is the high current part - it does the most work.

Note - don’t try this without the needed antenna analyzer to tune it.

Years ago I made one for my first build (as my only comm antenna). Flying next to another RV-8 using the Archer comm antenna I was needed to relay comms between him to ATC. I later replaced it during a panel upgrade, ending up with two belly mounted whip antennas. Same for the next three builds as well.

No matter what you do, the wingtip comm antenna will never be as good as a properly tuned belly whip antenna, but you can get by with it on your secondary radio (if a better option is not viable).

Carl
 
I appreciate all the input.
I wouldn’t mind a dorsal mount, but only if it works very well.
The antenna mounting instructions I can find all talk about keeping the antenna several feet from the vertical stab, so it doesn’t look promising…
I appreciate the info, and from this group, it seems that anything but belly mounts are pretty uncommon. (There’s probably a reason for that) 🤨
 
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