Thicker Antennas Change Things (
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- Опубліковано 7 лют 2025
- Pawel Kazmierczak is wondering if the thickness of an antenna mast, would have a wider bandwidth. He is also wanting some equations, if possible. Watch to learn more about this interesting effect.
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#dipole
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Thanks, it was me who asked that question.
Thank you for your financial support of this channel! It is greatly appreciated! 73, Dave, KE0OG.
I am not an antenna guru so take my opinion with a grain of salt. If I under stand it correctly...
The antenna is looking for resonance. If you measure a thin wire length, you can calculate the frequency. As you increase the diameter, you can still measure the length. But consider also, you can measure diagonally (Pythagorean theorem). Of course the length diagonally would be longer. That would make the antenna longer, causing the center frequency to drop.
Because the antenna is looking for resonance, it would find it anywhere from the length to the diagonal length. That is why the bandwidth would be wider.
KE0OG used 20m, notice on 70cm the length to diameter is more pronounced so the diameter will have more effect on the center frequency and width.
If my numbers are correct (1/4 wave), 435 MHz comes to 16.4 cm. If you use a 1 cm diameter, the length might change to 16.43 or the frequency to 434.2. Notice KE0OG's center frequency drops and the band width widens. Look at the width of the 2:1 SWR line to see width change.
I am not saying I am correct, just another perspective in hopes to clear it up.
It isn't looking for resonance, it's just that the electrical field propagates along a given length at a given (more or less) amount of time. But yeah, I guess that makes sense otherwise. Cheers.
@@WR3ND Thanx. I was implying that for the antenna to be properly tuned, you wouldn't have common mode current on the outside of the coax.
If I understand correctly coax will act reactive if the antenna and radio are different impedances. That is how a tuning stub works.
I ASS-U-ME the reason tuning an antenna length can get confusing if the antenna is out of resonance, the coax length can affect the SWR.
Always looking to have my misconceptions tuned.
"antenna is looking for resonance" is a sloppy comment (grain of salt), but intended to mean you don't want RF burns through you mustache. Or in my case, the smart charger on my sailboat gets reset by the halyard antenna when I transmit on 3.9 MHz
@@ny1t Ha ha, yes, we're the ones looking for resonance, just not the wrong sort. 😆 73
Dave, this was an interesting video on a topic most Hams don't think about much. Most VHF/UHF antennas have a matching network at the antenna. Also, a larger element diameter makes an antenna more efficient. I believe the original question was, "Why do thicker antennas have wider bandwidth." So, why do they?
The question opens a physics can of worms. But basically, a thin wire is really much better a resonator than antenna: it couples to itself at its resonant frequency much stronger than to free space. At the opposite end, a transmission line that _gradually_ opens up into a double cone couples very well to free space, and has a huge bandwidth. So of course something of intermediate shape will have intermediate bandwidth.
@@Matthew.Morycinski, for a thin conductor, there is only one path from end to end. For a fat wire or other shape, there are longer paths from end to end but no shorter ones. That's why the center of the SWR dip moves lower in frequency. The case of a radial mode helical antenna is another example of this. Many Hams use antennas with several wires running parallel but separated by spreaders to increase the effective diameter. (This works if the wires are not separated too much. Otherwise, the feed point impedance will be lower.)
@@RB9522 Yes, that's one rule-of-thumb way to look at it. But I would not carry this analogy too far. Current in a thick wire is no longer a line but a sheet. Charges at the ends are no longer linear but take up a complex shape. Even modeling this is only doable by turning this "simple" thick wire into a mesh.
True. Antennas are on the border between magic and theory. There are so many variables that sometimes the best path is to build and test.
Robert Wilson did a segment on Fat Dipoles in the ARRL~ More Wire Antenna Classics V-2.
Hey I kinda got away from ham radio and subsequently ham radio youtube for a while there, but I'm back and it's good to see you doing well.
I'm just in the early stage of your video.
Yes, I have observed that Wires/Conductors do vary in inductance.
Thinner wires have more inductance than thicker wires
of the same length.
Also the shape factors in too.
If instead of a round / cylindrical conductor like a typical wire, we use a flat & wide conductor like used as an earthing/grounding braid, it will have even lower inductance per unit length.
This is why gauge can change the required length & the resonance of the LC system.
One more thing is the wider gauge can have a wider range of paths along the conductor due to the thickness. (Broader)
Like being able to meander along a wider path instead of a straight line. Hense the broad banded aspect.
Woops hahaha
I have Rambled.
Keep up the great work mate.
⚡🙏⚡
You find the same thing with sound like in flutes, recorders, pipe organs... The 'belly' of the wave is normally just outside the pipe. The wider the pipe gets, the further out this belly is, so the lower the resonant note will be. I'm assuming that, since current runs along the outside of a conductor, the difference for hollow pipes or solid rods would be very small for antenna use, but I would be interested in actually seeing if that's right. I didn't know wider conductors made for a wider bandwidth. Good to know! I was thinking about making an antenna for my latest radio, the UV-K5(8), to optimize the receive range. Guess I'll be looking in to brass tubing instead of bicycle spokes for that one ;) Also makes tuning easier, because I can use two pipes that fit snugly together ;) Thank you!
Very nice analogy to sound waves in wind instruments. I also often apply a bit more intuitive sound waves physics to RF domain to make it easier to process. So I had all the pieces but failed to put them together. This however answers only the question why resonance point moves down. Why diameter affects bandwidth is still open. Experimentally I observed it but could not find any equations in the Internet so I asked Dave. He made very nice simulations and confirmed my obserwations but the question WHY remains open. Suggestions from other comments about more possible longer paths on a tube VS line antenna (geometry+quantum mechanics) is something I thought of before asking Dave, but the impact in that case would be minuscule.
Dave, you are a Master Instructor in anyone’s book. Another great video that not only demonstrated the results to be considered but opened our minds to more related questions like:
Does it matter what the conductor material is?
Does it matter if I use 1/4” tube or 1/4” solid rod?
Modern day James Clerk Maxwell 😂 I learn so much watching these.
Thank you for your financial support of this channel! It is greatly appreciated! 73, Dave, KE0OG.
I've always wondered if the reason why the antennae that were used at the Woodpecker site in Chernobyl were what looked to me like cage dipoles to maximise bandwidth.
This also explains why UHF antennae tend to have much broader bandwidths for a given element thickness compared to HF.
Really interesting video, Dave - thanks for the effort you put into making it. It also raises questions regarding the easiest way to match from a 50R transmitter to a 75R run of coax to maintain the best SWR and reduce losses in the feeder although I've not got much chance of getting a lot of relative height on 40m and below....
I've wondered for years why we don't use 70 Ω coax to match a dipole. There's a lot I don't know. A few rather long observations below.
I used to have a valve KW 202 rx and KW 204 tx 40+ years ago and a very short length of 75 Ω t.v. coax to my tuner for the long wire. I had a KW 75 Ω SWR meter because you could specify 50 or 75 Ω.
Is the modern tx really just 50 Ω out? Having built my own tx I can't see how it is exactly 50 Ω, it depends how many turns on the transformer. It might have been 60 Ω for all I know. I did just tune for maximum r.f. out much to the horror of my amateur friend, (no SWR meter). If the SWR is not known why worry! As it turns out max. r.f. out was minimum SWR when I did build an SWR meter.
i have tried a 50 Ω dummy load and a 80 Ω dummy load on my FT817 and as expected the 80 Ω wasn't liked. Is that only because the SWR indicators are set for 50 Ω?
Can a gamma match be adjusted for 50 Ω because we tap along to get a match so I'm guessing zero to perhaps a few thousand Ohms. Is that a great way to get 50 Ω on a dipole?
I built a 70 MHz 3 el Yagi years ago with a Gamma match, no SWR meter so who knows! A half Watt a.m. into Scotland so it certainly worked but I did have height.
G4GHB.
Regarding 50/75 ohm cable, why do we not use a 25:16 (5 primary : 4 secondary wraps) transformer balun(or unun). This would transform 75 ohms to 48 ohms.
Still watching...
Excellent Info & Video ⚡🙏⚡
Great question, most intriguing answer! Thanks!
Thanks Dave... very interesting keep up the good work... great channel...
A very thorough explanation. Thanks!
Most importantly with coax
is the dielectric.
That's where most of the loss is.
Foam Dielectric is less lossy than a hard plastic dielectric.
Ideally a vacuum between the inner and outer conductor lol
but that's hard to achieve.
The less mass between the two conductors, the less dielectric loss even under higher swr conditions.
Woops again,
I blabbed on and on haha.
73 de VK3VKE 🇦🇺
Love your work mate 👌👌👌
As a wire antenna is made thicker four things cause the resonance change. 1. The electrical length is increased as the surface area is increased. This drops the resonant frequency while creating a flatter bandwidth curve. 2. Self inductance increases with a thicker wire and impedance changes. 3. Capacitance become less which also results in frequency shift 4. Current distribution changes in a thicker wire and concentrates at the outer surface area especially at higher frequencies and this also reduces the resonant frequency.
Thank you David, I am going to download EZNEC and do some modeling.
By the way I have just built a homebrew 4 band moxon antenna, for 20, 15, 10 and 6 metres.
I fed it with 50 ohm coax and used 75 ohm coax to join the driven elements from one to the next. Tunes great on all bands.
David HS0ZQA Thailand
Can you share the instructions for that build?
73
D. C.
WP4TGK
Dave, Just found your channel, watched and enjoyed the video. It may only be my understanding, but talking about thickness of an element, is this the two dimensional measurement of a plane through the element ? My thoughts are that a 1 inch tube will have a height of 1 inch and a thickness of 1 inch, where a tape measure ( a wide one) will have a height of 1 inch and a thickness of maybe 0.01 inch. How will this affect the NEC modelling of a dipole? I have often thought of making a portable yagi using tape measure blades, but which would have the greater bandwidth for 2 m and 70 cm , a 1/2 wide blade or a 1 inch blade and what orientation? vertical (90 deg) to the boom or, the blade flat or in the same plane as the axis of the boom ?? Have never played with NEC software, so will have to get a copy running and learn how to use and understand it.
I seem to remember Yagi calc's involved diameter back in the 70's. I no longer have one of my ant handbooks from 70's, but I do remember some design's take into consideration of element diameter.
I remember hearing similar discussion around making elements out of Aluminum Arrow bodies rather than solid aluminum rods. It wouldn't work at any frequency where the driven the reflecting element needs to be larger than the length of the arrow.
Thanks Dave, will look forward to your results using 75 ohm coax to a dipole. 73, K7KS
Paweł, AFAIK no one looked for such equations except for very short (lambda/10) antennas. Professional antenna designers have access to good modeling software, and anechoic chambers where they test models, so the equations and rules of thumb are just a starting point for them. They don't need to use an equation when the simple answer is "come up with an idea, model, then test." - 73 od Maćka VE7EVE
That may be the answer - build and tune, build and tune. No need to publish.
"Trade secret" might also play a part.
Maybe indeed this is one of the problems that as of today has only numerical solution, mathematical solution is yet to be found...but its a bit hard to believe.
@@liamkaloy I agree - there should be a mathematical solution or at least an approximation. Putting this one under "Trade secret" because the both US and Russia used large cylinders for antenna receivers. Look up "The Woodpecker"
It was not just for Structural reasons.
@@liamkaloy Not really. It's a system consisting of conductors, insulators, charges and currents that all interact - with delays. They all connect through Maxwell's equations, but the result is usually neither simple nor predictable. Some configurations are nice and predictable. Others only look good, like the infamous "fractal antenna" attempts.
Having designed and built TV broadcasting antennas, it is essential to employ fat stubby elements to achieve the 7 to 8Mhz bandwidth needed for a single channel. Group delay needs to be kept minimal to ensure good quality balanced pictures. This applies to the channel filters, hybrid combiners and power dividers for the same reasons.
That’s very interesting, it looks like the bandwidth increased a little bit as well
Dave-
Another great informative video as usual, but I have an off topic question. What is that led light show going on over on your desk?
Many thanks.
73' de K4WRF
Hello Dave, I think if you research patch antennas you will reach the "real antenna" formula, a surface area formula. I am know engineer, but my oldest brother that retired from Lockheed Martin as an electromagnetics engineer working on avionics for military aircraft had to use the surface area formula.
Im using RG6 on my 40m slant-wire antenna, with which I have made a couple of QRP CW contacts from Central FL to North Carolina.
According to my NanoVNA, the SWR is 1.5 with an impedance of 60 ohms at the transceiver connection point. And i think it's 60 ohms because I had to shorten the counterpoise to less than 1/4 wavelength due to space restriction in my back yard.
I always thought using thicker wire made the antenna more wide banded I didnt know it would lower the resonance.
Am I remembering this correctly. Larger diameter wire has more inductance per unit length than smaller diameter wire. The would account for the lower frequency, would it not? By the way, the Russian Woodpecker antenna had a cage to give it really wide bandwidth. And I have used parallel wires separated by an insulator to increase bandwidth.
Try it Dave, I us to try on HF and VHF , RG6 cheap 75 ohm TV coax and work. Also this coax can handle 75W on VHF , it is maximum what I have. On HF I try 25W same because I have it. Usually I use better 75 ohm coaxial cable but RG6 is fine.
Thanks Dave! As always a great learning experience. ‘73 AC3EA
thanks Dave, have a great weekend !
its worth using Tube, I have a spool of HVAC 1/4, that is about the sweet spot, I am about to change out the thin stainless steel wire on my loop to tube
yes I suggest it for any band HF, MW, UHF, and VHF there is a little tuning but not much
The SWR curve seems to be flatter at larger diameters or am I wrong ?
Why...well, there are reasons. The big deal is that the wider the conductor the wider the bandwidth. Very cool. 'Cage' antennas use this principle quite dramatically and they aren't even solid.
Yes, I thought of a cage aerial for 10m to cover the whole band.
G4GHB.
A simple model can be as useful as a numerical model. It's the circumference not thickness that matters. Rather than a round wire think of unraveling the surface to a foil of length L and width W. As W increases, a signal can have multiple path length ranging from L to a larger effective L'. Because of this, it only makes sense that the band width increases and the resonance frequency decreases. Because of the skin effect, one should be asking the question of solid vs stranded.
That's what my wife says but I told her you're getting what you are getting...
TLW does have LMR 400 listed. It is listed as RG8 type, TMS LMR 400. Nice video.
I decided to make a dipole antenna that I could adjust to cover 10 to 20 meters.
I decided to use two 25 ft tape measures. They were 1 inch wide. I know that
the formula 468 /frequency is just a starting point so some trimming needs
to be done. I soon discovered that the spots I wanted to be resonance was
considerably shorter than my calculation and the bandwidth was fairly wide.
I was using an antenna analyzer to find the lengths along the tape measure. KF6EWO
As i have built antennas, i have noticed the same thicker wire = wider bandwidth.
How do you mount that heavy tube antenna?
Well, if its thicker the capacitance between the elements would increase for 2 reasons, the external wall area of the elements increases and the distance between the elements decreases. These would require intrgrals to find the rate of change as the thickness increases with the changing shape of the conductor. The resistance would decrease because of the volume per unit distance increasing. If you break the equations down completely, those changes might account for what youre seeing. By that logic, tube should have greater capacitance and resistance than solid stuff, more skin area and less volume per distance.
Does a telescoping whip create multiple "outer surfaces"" when not used at full length?
No.
I deleted my comment because I was afraid I wasn't correct. But I was. Two sources confirmed my opinion. The best source was an excerpt I found on the web, but it was unattributed. The second was in ARRL Handbook on page 20.3.
“If the diameter of the conductor is increased, the capacitance per unit length increases and the inductance per unit length decreases. Since the radiation resistance is affected relatively little, the decreased L/C ratio causes the Q of the antenna to decrease so that the resonance curve becomes less sharp with change in frequency. This effect is greater as the diameter is increased, and is a property of some importance at the very high frequencies where the wavelength is small.”
I saw a video on making a vertical VHF/UHF dipole with 1/8 inch stainless steel welding rods. I got some 1/8 inch stainless steel welding rods but have not made them yet. But I found some 1/8 aluminum rods. I don't have the software to run the models on them. what do you think would make a better antenna, The Stainless steel rods or the aluminum rods! The antenna would have a VHF& UHF going up from a PVC pipe and a VHF& UHF going down from the PVC! This is done by bending 2 - 1/8 inch to have a longer and a shorter. Longer cut for VHF and shorter cut for UHF. Would RG6 quad shield be good to use on HF! 73 W4DES
I have always understood that the thicker the antennae elements are the broader the bandwidth of the antenna is. But what do I know? I could be wrong.
So, say if you have the ETON 750 & you somehow replaced that antenne with a skinnier one, would that lessen the scope of the wide bandwidth it's known for? It's something like a width of 14.
@@migi5374 It's not the the bandwidth of the radio it's the bandwidth of the antenna.
@onmyworkbench7000 help me here, the antenne draws in for the radio, NO?
@@migi5374 The radio has a range of frequencies that it can receive regardless of the antenna, however if you are trying to receive a range of frequencies that the radio can receive but the antenna is not designed for then the radio will not be able to receive that frequency range as well as it would if you were using an antenna that is designed for that frequency range. By using thicker antenna elements it allows the antenna a wider bandwidth therefor allowing the combination of antenna and radio to receive more frequencies than an antenna with thinner elements would do.
In my brain, the thicker the antenna elements, the more virtual paths the current has to choose from. So the thicker the wire, the longer the wavelength you can 'cram' in there. But those paths are only longer than the wire, never shorter, so the thicker the element the lower frequency of the optimal SWR.
I doubt this is actually what's going on, because why would the optimal SWR stay nearly the same regardless of pipe size?
Many years ago I saw a paper that considered the length/diameter ratio. It included an equation that was about 3 feet long. I've looked for it again many times with no success.
Dave, wouldn't wire thickness be accounted for in the velocity factor as provided by the manufacturer? de Brad KC6NNV.
The really wild thing is using the GEOMETRIC FRACTAL ANTENNAS.
Do you know of modeling software for these? I would love to try them as circuit board antennas at ehf frequencies.
You might find the equations you seek by looking for cage dipole modeling.
It's like a guitar string - a thicker string will have a lower frequency. At least that's what I'm hearing.
This guy did the whole video, and the letter: "Q" never came outta his mouth. Higher the Q, the lower the width of that he'll curve. Think of it as a tuning fork. The best tuning fork will ring, with a gentle tap, at a single crystal clear tone. That's high-Q. Now, start adding mass to that tuning fork. Still rings needs more of a thump and damped out way quicker. Mid-Q. Add enough mass, at it probably not even be worth hitting it on something. Did it make a sound, yep. Does it sound like a crystal drinking glass nope. Even low Q dioples will push out a field if you push it hard enough. Wider radiators have more surface Area, trying to "push a rope"
Mag. loops are a high Q and very narrow tuning range. I've built a couple of them.
G4GHB.
It is all in the ARRL Antenna book.
Or if you really want to dig in, in the Antenna Engineering Handbook that you can find at a nearby techincal college library.
@@Matthew.Morycinski ISBN 007032381X? 2 decades ago I went through earlier editions of ISBN 83-206-1626-3, which seems to be your recommendation equivalent. Maybe first I go back and check there. I remember that one was not an easy read.
Thicker radiators have flatter SWR curve. My 3.5” flagpole antenna has a flat SWR curve.
Are we sure these changes are a function of width and not mass?
Yes, rf travels on the skin of the conductor, cares not whats in the center.
@@tahlularose9267how can we prove this?
Called K factor
FB OM TNX 73
"Why do thicker antennas have wider bandwidth." So, why do they?
73s sir
Thank you, Dave.
That was interesting and new to me. N0QFT