HF Antenna in Carbon Fiber Plane

jnmeade

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Display name:
Jim Meade
I'd like to communicate person to person with someone who has direct personal experience designing, installing or using an HF antenna in a small, carbon fiber airplane. Emphasis on system design, installation, hardware and so forth. Not concerned about the theory or frequency coverage or use. Private message is fine if you prefer.
 
What wavelength? HF covers a wide frequency range, defined as 3 to 30 mHz. Wavelengths from ~100 to ~10 meters.
Paging @weirdjim
 
installing or using an HF antenna in a small, carbon fiber airplane.
FWIW: we installed/used a number of HF systems on metal/composite helicopters. How it was installed and how it performed was more subjective to the specific radio system, i.e., antenna type, number of system components, freq., power, etc., than the type of airframe/aircraft. Perhaps select a top 5 list of HF radio types/systems you want, then see/question how it will interface into your specific aircraft?
 
What wavelength? HF covers a wide frequency range, defined as 3 to 30 mHz.

That's an AWFULLY low frequency -- 3 to 30 milliHertz. 3 to 30 MHz.?? :aureola:

Paging @weirdjim

WeirdJim ain't gonna touch this one for a couple of reasons.

1. The op wants to communicate "person to person". That means that the rest of the newsgroup is deprived of any useful information that might come out of the conversation. That is just plain selfish. And wrong, because if I make a mistake there are a dozen people around that will catch my error and correct the information.

2. If this is for the noncommercial amateur ("ham") band operation I have no problem sharing what little skills and designs I know for free. If this is for a commercial use I'll be happy to share my professional fee schedule. Just let me know.

Jim
 
Yeah, I meant megahertz :)
I think I got the wavelength range correct for the frequencies I was trying to describe:)
 
Ditto Jim’s sentiments other than I won’t even do it professionally. Ha.

Been tinkering with HF on ground pounder vehicles for decades. It’s a pain in the ass and always a compromise.

The best performing small aircraft HF system I’ve seen installed was a replacement of the ADF long wire from one wingtip to the center insulator, to the tip of the tail ... with a decent tuner.

The other I’ve seen used is just trailing a long wire. Same deal.

Neither performed anywhere near even a compromised ground based antenna. Which don’t perform as well as a good ground based antenna.

A helicopter sling loading a big Yagi at the right altitude would probably work spiffy though. :)
 
I tried my level best to get Voyager to use the old "bare copper wire and Dixie cup out the bottom of the fuselage on a fishing reel to resonate" trick but they opted for the King stinger on the vertical stab. I still don't know what they used for a counterpoise -- copper mesh inside the stab? On a black glass ship I'm guessing that they would have better luck with a low-r glass fuselage for the ground plane and either (as you suggest) long thin wires from wingtip to vertical fin to wingtip or the old Dixie cup trick. Then again, the op wants proven techniques.

They don't call these aircraft "experimental" just for the hell of it.

Jim

p.s. They DID use nylon cable and a fishing reel to haul up the gear. That was Jeanna's job. I made her up a name tag at Oshkosh '83 that read, "Wench With A Winch". That didn't go over so very well.
 
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Many moons ago, when I had a C-172, I ran "magnet wire" from wing-tip to vertical stab to the other wing-tip. Fed with RG-58 running up through the stab and connected to a good tuner. I used my ICOM 720 on 20 meters and it worked great!! STRICTLY A TEST, OF COURSE!!!!
 
Many moons ago, when I had a C-172, I ran "magnet wire" from wing-tip to vertical stab to the other wing-tip. Fed with RG-58 running up through the stab and connected to a good tuner. I used my ICOM 720 on 20 meters and it worked great!! STRICTLY A TEST, OF COURSE!!!!
Jim,
What is "magnet" wire? I was looking at copper clad steel stranded, but I see some ADF sense wire is solid. That surprised me.
What gauge wire did you use?
What did you use for strain relief (wing flexing, wind on the wire, etc.)? Anything like the stuff here?
https://www.dallasavionics.com/adf/adf.pdf
Where did you put the strain relief? On the wings or on the vertical stabilizer or both?
Of course a tuner - what did you use?
Did you try on any frequency other than 20m? 20m is about the biggest that will work well on a small airplane, as as it's carbon fiber and thus no counterpoise, it would have to be a V.
What problems did you encounter with the setup, if any? One doesn't want an antenna wrapped around a control surface. :(
Thanks
 
Magnet wire is typically a lacquer/enambel-covered thin wire used to wind transformers and electromagnets. Usually very thin gauge. You lose a little broadbandedness for small (when wound up) and light.
 
I don't recall the gauge of the wire, probably #20 and it was as described above, i.e. enameled wire. At the wing tips I used a fiberglass tent pole (1/4 inch by 33 inches) from my kids "play tent". There was a metal ferrule on one end through which I drilled a hole, attached a small "s" hook to the wire and attached the hook to the ferrule. Under the wing tip I removed 2 screws, put 2 plastic cable clamps on the fiberglass rod then secured the rod to the wing tip with the plastic clamps. The rods provided enough "spring" to be a strain relief. At the vertical stab I just soldered the shield and center conductor of RG 58 to the wire coming from the wing tips. The coax was secured under an unused ADF long wire bracket. I did try loading the antenna on 40 meters but that wasn't a good match. But 20 meters and higher worked well! I rationalized that if the wire broke it was so small that it would streamline in the wind and not impact the rudder. I'm surprised I still have some of these things around (not really, I NEVER throw things away) so attached are 2 photos showing the fiberglass rod and the wire. It was a fun experiment, after all that's what ham radio operators who are also pilots do, right? IMG_3410.JPG IMG_3409.JPG
 
My fiberglass boat has a loop antenna for the SSB and it works quite well. SGC 2000 radio and 230 tuner. It uses a backstay from the mast for the antenna, probably around 65 feet long. I believe the backstay is 3/8".
 
Not that it adds much to the discussion of HF antennas in aircraft, but here is an article I wrote for the ARRL about twenty years ago.

Jim
 

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That same C-172 I owned has even today an aircraft "bent whip" antenna trimmed down to resonate in the 144 MHz band mounted to the top of the fuselage behind the rear window. The current owner had no idea what the antenna was for but left it there rather than fill a hole! Thanks for the article, Jim!!
 
I still have Dads 2m antenna that he used on his 182. I bet he got the mounting idea from you. He also had an RST audio panel that he ordered, and put together. It had marker, and intercom. Mine only has marker. I may install my Azden 2000 in the Cherokee, but it doesn't do ctcss, and pretty much everyone is doing that nowadays.
 
And be willing that to bet the OP isn't experimenter enough to see whether the carbon fiber body is ground plane enough to do an HF antenna for his purposes. EVERYBODY else has to do the experiments and share with the rest of us so that he can't just trade on somebody else's ideas.

This is my 45th year doing experimental antennas and I've had data from Rutan, Rand, and all the rest of the experimentals of the 1970s including one really experimental from 1967 Apollo that defined my antenna chops.

I think I know what I'm doing.

jim
 
I would think you might just well know what you're doing. You do it for a living, I just play with it.
 
Initial investigation is very tentative. Aircraft is carbon fiber reinforced polymer (CFRP) covered by a coating inside and out and I'm not sure if it is isotropic or anisotropic but the latter makes sense.

Using an ohmmeter and measuring resistance between random points a couple of feet apart on the outside, on the inside, and between outside and inside indicated infinite resistance. Testing between several unconnected metal pass-through fittings showed low resistance. Obviously the coatings are non-conductive but the CFRP appears to be conductive and can be accessed by using a conductive fitting that is attached to it.

The airplane manufacturer rep said his experience was that ADS-B antennas could be installed with no ground plane. That supports the CFRP conductivity assumption.

Here are two papers by the Technical University of Wien that appear to be oriented at investigating the use of 1-10 GHz antennas in car bodies.
https://www.researchgate.net/public...as_antenna_ground_plane_material_up_to_10_GHz
https://www.hindawi.com/journals/ijap/2017/6152651/
They make the point that anisotropic CFRP is necessary to avoid distorted signal distribution.

A good friend who is a retired Collins Radio antenna engineer suggests that while CFRP may be OK as a ground plane in the 1-10 GHz range as supported by the papers, that may be different in the 3-30 MHz range of HF.

Another good friend, also retired from Collins, was a project manager on the Collins radios for the Beech Starship project a couple of decades ago. He says
"We used UHF and VHF antennas on the Starship with no big problems, aside
from the problem I mentioned about keeping a corrosion-free contact with
the carbon fiber material itself. I'm not primarily an antenna person, but we
always thought of it as a wavelength-dependent property. Where the
wavelength is short with respect to the airplane it seems to work; no
serious problems with antenna gain, range, pattern, etc. with VHF Com and
Nav or with UHF transponder, DME, GPS, GLS, Marker, etc. (GLS was a
symmetrical horizontal dipole, not using a ground plane.)"

He goes on to note directionality in the ventral fin mounted VOR antennas which had bearing and bank-dependent errors at ranges over about 75 miles ahead. He attributed it to the VHF signal not "bending" as it followed the skin of the Starship. (It could also be affected if the Starship layup is isotropic but that seems unlikely to this layman.) (Note he mentions problems with maintaining a good connection between the antenna feed and the CFRP, which could be an issue to those who install an ADS-B antenna with no ground plane, relying on good conduct with the CFRP via the through-fitting.) For my airplane, the wave-length is decidedly not short in regard to the ground plane.

The best producer of through-hull fittings for my needs seems to be Dayton-Granger. Their web site is not helpful but they sent me a thumb-drive of their catalog which is very useful.

A dipole mounted from each wing-tip to the top of the vertical stabilizer will match very nicely with the 20m band, about 14 MHz. If the CRFP hull would be an adequate ground plane I could probably match a 40m or 7.0-7-3 MHz antenna well.

The radio is likely to be a Yaesu FT-857D because I have one and there isn't much better at an inexpensive cost. I have an acceptable tuner. They will be mounted in the baggage area and a control cable run forward to the control head. The microphone will be picked up by a PS Engineering TAC 12100 which handles the impedance matching and fed to a PS Engineering 8000C so it acts just like any other aviation radio and can be selected as one of the radios, heard through the headset and uses the headset boom mike.

I'm going to model both a monopole using the CRFP as ground plane and a dipole. This is not going to happen for a couple of weeks or even months at the earliest. I'll post the results when I have them.

Thanks for those who made suggestions.
 
The fibers in carbon fiber composite construction are not in contact with each other. There's both a non-conductive sizing as well as the epoxy that's holding it all together. So at the DC level it's not conductive (and that's all your ohmmeter test shows). As to what happens in an RF environment, I'll leave that up for others to experiment with I suspect you're going to get some amount of coupling. The fibers are going to tend to be long enough at the VHF/UHF frequencies, can't vouch for HF.
 
I'm not an expert on CFRP but when they talk about anisotropic construction it's hard for me to not think of the fibers as touching. My ohmmeter test was on the "skin" if you will, so never touched the CRFP. There was good conductivity at the DC level between non-connected metal through-hull fastenings. As you point out, that may be irrelevant at the RF level. In any case, for whatever reason, 4 citations in my longer post talked to CRFP as a ground plane in the GHz and VHF/UHF frequencies. When I get to it, I'll post the results of my experiments.
 
Not that it adds much to the discussion of HF antennas in aircraft, but here is an article I wrote for the ARRL about twenty years ago.

Jim

Did ARRL publish that article? Seems a bit on the long side for QST. QEX, perhaps?

Also, the last paragraph on the first page isn't quite right. 91.21 says that you have to make sure that portable electronic devices don't interfere with communications or navigation equipment when flying under IFR. Not a problem or requirement with flying VFR. That said, as an EMC engineer with 44 years experience I turn off my cell phone and ensure that everyone else in the plane does so, as well. I know about the required measurement in ensure that there isn't interference, and I'd rather spend my time flying. :p

Good paper, however.

73

N6TPT
ARRL TA
 
not an expert on CFRP but when they talk about anisotropic construction it's hard for me to not think of the fibers as touching.
Why? Anisotrophic just means the fibers are aligned, not necessarily that they are in contact with each other, which they are not, as I stated, there are two things (the sizing and the resin) that are insulating the strands from rich other.
 
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