backcountry
Well Known Member
I understand there’s VOR antennas that can be bonded on the inside fiberglass and wonder if anyone has tried that inside the RV-12 engine cowling?
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VOR antenna
- Thread starter backcountry
- Start date
Might not be enough space -- but here's the thinking:
Fashion a dipole cut to the center frequency of the VOR air band (108MHz - 117.95MHz) using 1" copper tape for each "leg". Glue each leg to the underside of the cowl -- each leg will be ~24" long. Mimic a cats whisker VOR antenna by angling each leg about 40° aft. and you should get the impedance to about 50ohms.
Use a VNA or SWR meter (MFJ 259D) to check your work. Because it is a dipole, there will be "nulls" in the reception of stations directly aft of each antenna leg.
backcountry
Well Known Member
Thanks, I may try it
Carl Froehlich
Well Known Member
Ignition noise may be intolerable.
Carl
Carl
I just read this thread and I performed some testing and analysis on various VOR antenna concepts today. An antenna mounted on the cowl has some problems associated with the proximity of the engine (heat and electromagnetic scattering from the engine). An alternate approach is to mount the antenna on the inside of the aft canopy. A while back I built a VOR antenna with an integrated balun mounted on a piece of cardstock. I placed this on the top of the aft canopy and used a vector network analyzer to measure the voltage reflection coefficient of the antenna from 100-130 MHz. The attached photos show the installation and measured data. The measured data is the voltage reflection coefficient in dB over the measurement band. Good performance is associated with the portion of the trace along the bottom of the screen. The antenna has been detuned by the structure and could be easily trimmed to center the good performance over the 108-118 MHz band. I also performed some numerical analysis with FEKO and attached is the computed yaw plane performance of the antenna (nose is at 3 o'clock). The feed line could be routed down the roll bar support structure. The balun could also be mounted to this structure making a very clean installation.
Attachments
Carl Froehlich
Well Known Member
Why put one of these ugly eye pokers on your airplane when a wingtip VOR/LOC/GS antenna fits the bill? Mine works to 100nm+ out and LOC/GS way beyond practical range.
Carl
Like Carl, my wingtip mounted 30-year old Archer nav antenna works to a longer distance than needed.
bbaggerman
Active Member
Do you recommend putting your wingtip antenna inside or outside the RV-12 metal wingtip?
bbaggerman
Active Member
I haven't done it (I'm going the WAAS GPS only route) but I understand routing that antenna cable up through the tail is a non-trivial task.
My intention was to show an alternative approach to the VOR/LOC/GS antenna installation for the RV-12. Thin wires bonded to the inside of the aft canopy is an easy installation. Routing the cable to the receiver is also easy compared to a wing tip or vertical stab installation. And the antenna performance is every bit as good as the conventional locations.
Cool...How much does the departure from the horizontal plane effect efficiency?
Just thinking out-loud -- I can't think of a reason that you couldn't repurpose the "boomerang" VOR antenna from a Beech ABEFGV-33/35/36 and mounting it under the belly of the -12 in a suitable spot...
Or, use the Comant CI-120 "blades" up on the vertical stab ala Mooney.
Both of the aforementioned are available from the various aircraft salvage companies for much much less than new, and you get to give new life/purpose to something...
Cheers!
B
Carl Froehlich
Well Known Member
My numerical analysis shows little efficiency difference between the various approaches. The wind tip concept has a reduced antenna gain value on the side opposite from the antenna location. But all of the changes are negligible when examining the RF link budget as there is plenty of margin available. The window mounted approach avoids cutting holes and routing cabling in structure.
