Ideally, if you are going to transmit, you want a properly-tuned resonant antenna. But, sometimes, it isn’t practical. [Ham Radio Rookie] knew about random wire antennas but didn’t want a wire antenna. So, he took carbon fiber extension poles and Faraday tape and made a “random stick” antenna. You can check it out in the video below.
We aren’t sure what normal people are doing with 7-meter-long telescoping poles, but — as you might expect — the carbon fiber is not particularly conductive. That’s where the tape comes in. Each section gets some tape, and when you stretch it out, the tape lines up.
We aren’t sure how these poles are constructed, but the video claims that the adjacent sections couple capacitively. We aren’t sure about that as the carbon fiber won’t be very conductive, but it probably isn’t a very good insulator, either. Then again, the poles may have a paint or other coating along the surface. So without seeing it, it is hard to say what’s coupling the elements.
He admits this is experimental and there is more work to do. However, it seems cheap and easy to setup. The hardest part is tapping an M10 hole in the end cap to allow things to mount.
We suppose you could make your own tubes, but it hardly seems worth the trouble. If you cut or drill this stuff, you might want to take precautions.
im more interested in the measurement accuracy of that tattoo over time.
It’s in inches so it doesn’t matter.
Hence the term “freedom units”, you have the freedom to interpret them however you want.
One of Adam Savage’s videos on Y’allTube answers the question about his.
I haven’t watched that one though…
Just like any marked ruler, it’s for reference use only – not precision nor accuracy. It’s just REALLY convenient as you always have it on you ;)
Exactly!
Great question and I don’t expect it to be any more than accurate within a 1/8 for my lifetime.
If he’s tuning it it isn’t random, and a MUCH better (smaller, lighter, more efficient, easier to adjust) approach is to use something like this:
https://www.dxengineering.com/parts/cha-ss17
Somewhat shorter though
Looks like a perfect application for cheap telescoping glass or carbon fibre fishing rods.
It’s capacitively coupled precisely because the carbon fibre is not very conductive. It’s the dielectric in the sandwich between two pieces of the conductive tape.
Some cf is pretty conductive in some directions and resistors make poor dielectric so without knowing the characteristics of the pole, I’m not sure.
I can tuna fish, don’t mean it will radiate well.
I’m gonna tell Aunt Anna that you made a bad pun!
True but I have 6000+km contacts on it at 90W so I would say it radiates ok
If there’s no electrical connection between segments, the overlapping part acts like a capacitor.
A sample air-dielectric one with 4 sq-cm of area and 1mm of separation provides only 3-4 pF, but if we use carbon fiber dielectric instead, it should go up significantly. Looks like the permittivity of CF depends on many factors, but we could easily land into capacitance of a few nanofarads, which is an impedance of just few Ohms for HF radio frequencies.
In a current-fed antenna (dipole, GP), the part close to the feedpoint is the high-current one, then the ends carries almost no current (but significant voltage), so minimizing the ohmic loss close to the feedpoint is crucial for performance.
So yeah, I was skeptical at first, but the math says it can actually work and and save the amateurs from having to untangle a piece of wire. Still, assessing the performance of HF antenna is super hard, since variations in propagation far exceed the small differences in the antenna efficiency (unless you average over a long enough period).
Yes that is a battle for me for sure. Trying to prove the antenna is going to be a challenge
Those poles are great when you want to do RF safety measurements. Doesn’t carry touch currents and doesn’t cost measurement uncertainty budget. Also very light.
Paint roller extending poles can be useful as well.
telescoping carbon fiber is used for all sorts of fishing poles. I’m delighted to see other hands experimenting with this sort of thing. 73 de ac4rd!
73 VE6SFX
Carbon fiber structures make excellent absorbers of RF power: Conductive enough that you can’t transmit or receive through them, and lossy enough that they can’t be used as reflectors, radiators or transmission lines either. You can’t make an antenna or dish out of carbon fiber without shielding it with metal, and you certainly can’t make a radome with it.
If that carbon fiber is anywhere in the RF field it’s going to act as a dummy load (and make your SWR look great!). But if you short it out with a parallel conducting tape, then you’ll largely shield the carbon from the RF and not suffer much loss. Even the “capacitive coupling” he speculates about can work, because of the insulating layer of epoxy over the carbon fiber layup.
Paul then how do you explain me getting 6000Km contacts on it with 90W?
My second paragraph above: if you short it out with a parallel conducting tape, then you’ll largely shield the carbon from the RF and not suffer much loss.
Essentially the same as what Col. Panek says below.
Watch the video and then go to the links in the bottom of the video it does not absorb nearly as much as people claim
Tapes vary, but you should have less than an ohm on a segment. So put your carbon fiber resistor in parallel with that, and how much dissipation is the carbon going to absorb? Probably not even going to change the Q measurably.
The demo in the video inserting the CF tube through the two coils you mean? What do you think should happen in that case? What do you think might happen if you stick a highly conductive solid copper wire in its place? More loss or better coupling? That is not a way to measure the loss.
Loving the libertarian antenna (pun intended).
Very nicely made and can be used for other antenna types as well. He says at the end that it still works if you drop antenna’s in so I’m wondering how effective it is when you do that. Reaching Italy from western Canada with this antenna is much better than I expected.
Also, I love the measurement tattoo as an idea. I’ve seen it on Adam’s video’s. I just never liked the look of it. The best one I’ve seen online so far was a fish tattoo with a ruler through it. I need to look into this further.
A couple decades ago I built an 11 meter (CB) antenna out of an old fishing pole, wrapping it with magnet wire and some desoldering braid on the bottom end. It worked OK mounted on my car (1974 Dodge Colt).
Love this!
I don’t understand how the author of the video as well as so many folks here don’t understand that lossy dielectrics like carbon fiber make lossy capacitors … and in this case they are all in series with the current flow. It doesn’t matter whether the carbon fiber is coated with epoxy or not … the displacement currents in the capacitor pass through the carbon fiber that makes up the bulk of the dielectric. It’s literally Ohms law at RF. Without some sort of A versus B signal strength comparison with an actual conductive element this “antenna” looks to me like just a very long RF leaky dummy load.
did you watch the video? Did you see the links in it? Also how would you explain a 600km contact with it on 90W ?
Nope the author here… Then how do you explain a 6000Km contacts via ssb using it? This is far from a dummy load. If it were just the carbon rod yes I would agree but the faraday tape makes a massive difference.
I watched the entire video. It’s not a demonstration of anything. People have made contacts MUCH further than that with FAR less power than 90 watts with very marginal antennas … albeit much more EFFICIENT antennas than yours. Just prior to Field Day one year I made a solid contact with an FR5 station in the Indian Ocean from a poor location in Arizona (terribly lossy sandstone ground) with a poor vertically polarized antenna (long vertical rectangular ten foot high loop with the lower side literally two feet off the ground. That same antenna gave me by far the worst Field Day score I ever had from that same location.
An anecdotal contact is NOT evidence of anything as any knowledgeable ham will tell you. Why won’t you do some actual signal strength comparison tests versus a real vertical??
By the way, I just looked up a typical value for the loss tangent of carbon fiber (it varies, of course) and it is at least 100 times more lossy than other materials commonly used as insulators at HF frequencies. The test done by G3CWI doesn’t measure what he and you think it does.
Doesn’t the capacitive coupling between the sections change the phase for each section?
that is something I will need to research for sure.
pretty cool could take the hassle out of RF transmitting don’t ya know
I’m sticking with the teeth God gave me.
This past Spring I had a crown replaced.
They were able to give it a nice color.
Now, I surprise people when I show them that I had Bluetooth installed!
My wife says that explains the voices in my head!