Fascinating - Skin Effect and Cage Dipoles & Verticals for Wide-Banding Dipoles and Verticals
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- เผยแพร่เมื่อ 11 ก.พ. 2024
- A cage dipole is a number of elements spread out in a "cage" all connected together to make effectively a larger "skin effect" (surface area) antenna. John and I look at two solutions for wide-banding antennas. We also discuss skin effect and consider if this is the success of the DX Commander? Answers on a postcard please! Callum.
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It has been a while, but I had a cage dipole on 80m. 1991. I don't have any "technical" measurements. As I recall, I had 8 wires, held apart by 8" pvc slices. The bandwidth was 3.7 to 4.0. I was a Navy MARS operator as well, and could get below 1.5 to 1 even at 4.2 MHz. It worked like a champ. If I had the space, I'd do another in a heartbeat! I also had the advantage of being on a hilltop. Then I had to move to Florida and couldn't replicate it there.
Good comment!
Hi Callum. Serendipitously, only two days ago, I decided that I wanted to add another wire to my DX Commander so that I might be able to work the 29.600 FM calling freq. I added it along with the current 10m antenna that I have tuned to ~28.450. Once the second wire was trimmed and tuned showing ~29.600 resonance, I tried it out. I was amazed at how much broader the 10-meter capability had become! I don't have a complete usable bandwidth laid out on paper, but overall the two wires have caused the bandwidth coverage to become much wider. So, it sounds like in effect I accidentally created a cage dipole for 10 meters... LOL what fun!
Fascinating. Thanks for the analysis!
Absolutely delightful seeing her get on. Maybe I should show my kids this so they'll get off their bums and study. Cheers, 73 KS5KY
Callum, (And anybody else that would like to chime in). You and I logged that day when you did the remote session out of Canada. I mentioned I was running 10 watts fed into a Downspout on the corner of my apartment building. Keyword is apartment building in that I cannot erect any kind of an antenna on the property. The setup is a two-story downspout with a 9-1 and only about 20 ft of coax from the station. I don't have an RF choke on the antenna end of the coax in hopes that the skin effect on the coax will give me some kind of a radial. I do have a ground stake at the base of the downspout. With some heavy copper magnet wire, I've tapped onto the downspout about 20" from the bottom with a pop rivet. The system is flat resonant on 40 M and tunes reasonably well on all bands except 20.
My success with the antennas phenomenal on FT8. I'm reaching South Africa, Estonia, Israel and Japan(just a few) from North Carolina. On SSB the EU, points in South America and the Caribbean. All with 10 watts. So I can't complain. The surface area of a 2"x4"x30(approx)ft aluminum downspout must have a tremendous skin effect to get these results.
The question is this...By altering the pop rivet tap position, up or down, do you think I might be able to get a workable tune on 20 M? Or should I consider an industrial strength external tuner?
I would model this on the computer but I can't figure out how to represent a "piece of pipe" in the software...Anyone?...Berend KN4VUP
OK.. So if the COAX connection point changes, then the length of the radiator will change, but if you instead moved a jumper, then the jumper wire is part of the antenna. So it would have to be the feedpoint change, yes. PS - Love the system!!
So what you're saying is to Vary the point at which I'm tapped into the downspout.. The system has really caught me by surprise for 10 watts and the coverage I'm getting it's pretty amazing. Thank you enjoy your day ...Ber... KN4VUP
@@DXCommanderHQ
I did something like that on 11 Meters back in the 70s. I made an 5/8 antenna from 4 inch copper pipe. The receive was amazing for just being on the garage roof.
Wow!
@@DXCommanderHQ It didn't cost that much. Copper was super cheep in the 1970s that 4 inch copper was used. probably came from some commercial building. Are you still going still going to build a six vertical?
I remember looking into performance vs. wire gauge and coming to the conclusion that at HF, 'wire is wire': the ratio involved just didn't matter from 28 gauge to 12 gauge despite what the old timers will try to tell you - 'oh, 28 gauge wire will never work...' But now, making a cage . . that has my wheels turning! Fascinating discussion, keep them coming!
That's what I thought.. You would have to make it VERY large.. But not (yet) done the experiment.
Great video and discussion!
Glad you enjoyed it!
that was great ! the magic of RF. I did see a fan dipole multi band made out of Christmas lights. the surprise was they all light at different brightness on different bands. showing that they all radiate some what. the resonate one lights the brightest. and that was Josh from ham radio crash course a few years back on a Christmas special making a antenna out of Christmas lights and putting some power down the wire. look at that big antenna in Ukraine from the old radar system. lots of caged dipoles . covered the HF spectrum and Hurd all over the world. called the Russian woodpecker. used a caged dipole array . 73's
btw I heard the ruskies are up to something again. I don't remember the channel but there is a uk guy doing sw listening and he found it. I spun the vfo over and sure enough there is something there.
Skin effect is the distribution of current through the cross section of a conductor. As you go up in frequency more of the current travels near the surface. By the time you get to mm wavelengths the current is in a extremely thin cross section layer near the surface. Surface roughness of the conductor also plays a big role in skin effect. Mike KC3OSD
Thanks for sharing!
Yes, I found large diameter elements have very wide intervals with very low reflected power. I like using aluminum tubing from salvaged lawn furniture and better yet is 4 inch diameter aluminum dryer vent tubing.
I added a wire to a standard multiband vertical and had plenty of supplies to add a cage as the wire on top the vertical. The 8 wire 8 inch diameter cage ended up being 10 feet long instead of 20+ feet so there's that.
A Caged Commander?!?, I did not expect to hear that brought up today. A caged dipole kinda looks like a dxc on its side anyways. MMANA anyone.. :)
Interesting subject. I would think that adding wires is a case of diminishing returns vs weight. Best to you both and the Expedition is going up as soon as the yard soup drains off.
I've done this a long time ago, with a vertical antenna. Two driven wires with 15 cm spacing. (don't think this was important) but I made one wire resonant on one frequency and the other wire a little bit longer (resonant on a lower frequency, for 10 meter band) . There were two dips next to each other, on the analyzer. The bandwidth was much wider than with one wire.
Interesting!
Better than a Cage for wide bandwidth would be Fan Elements cut to different frequencies within the band you wish to widen out. The SWR plot would be a series of dips instead of one dip across your wanted bandwidth.
73 mike
Interesting analysis great video
Thanks!
What you are doing is to reduce the Q of a tuned circuit where the "circuit" is a radiating element. The near field caging effect has to do with capacitive coupling of adjacent elements as long as both elements are driven. I would think that two different lengths will create what looks like a Butterworth shape. This can probably be modeled with Fourier analysis.
The problem with reducing Q is that it affects gain by spreading out the bandwidth.
Fourier analysis. That'll be new to me - but the regular modelling shows almost same as a q/wave mostly.
Great discussion. You danced around what I feel is the issue with 160 and 80 meter antenna bandwidth and that is their wavelength. If you compare the calculated length of the antennas at the band ends, there is a much larger difference in the length for 160 and 80 than there is for 10 meters. Just my thought on the subject. Have a great weekend.
73 - K1AUS
I have an 80M Delta Loop hung in a vertical orientation, fed with a 4/1 balun at the feedpoint which is at 15M high. 1.28/1 at 3.780. 2.3/1 at 3.500. 1.75.1 at 4.000 mhz. With a bit more wire in it, I could move the dip down a bit and be well under 2/1 across the entire band. As it is, the internal tuner, it's good to go. I seldom operate above 3.800 though. As a Canadian amateur, we have the full band available to us. Next I will be adding an inductor from the middle of the bottom leg to ground to make it at DC ground potential. The same as I've done with my vertical. The bottom of the loop is about 10' above the ground.
Very interesting!
Skin effect, lol. Skin effect is where the RF flows on the skin of the metal, not the entire metal. If your having RF bleed, you can possibly control it with ferrite and shunt it to ground.
I used to run a high freq tube mill that used a liquid cooled oscillator tube as big as a 5 gallon bucket. It wasn't fun picking up your tools and seeing little arcs jump to the steel base of the mill. A exceptional ground network, and the ferrite controlled the flow of the RF in the pipe as it ran.
I feel sorry for Kevin Loughin. I've followed him on TH-cam for quite a few years and he's been struck down with Long Covid and he's had issues with his camper van. I wish someone would organise a Go Fund Me thing for him so we could help him out.
Yes.. Tom and I helped out with his fuel bill before this. I'm hoping he pulls through OK..
My concept of a DXC vertical "CAGE" antenna would be for primarilarily a single band (and its derivatives) and be at least 8" in diameter (or more) with at least 5 or 6 equal length wires (or more). - I don't think there would be a need for mulit-length wires to cover most of a wide band, as the added bandwidth from the diameter should be enough.
Let the experiments begin! - Co-incidental cages? - Stacked cages? - The "sky" is the limit! - lol - Cheers!
Yes, I think I probably agree with you after having some conversations beyond TH-cam..
You vision is very close to what I had envisioned. I think the current plates for feed and radial are sufficient. ^ wires seems to work well in the modelling so far. Working through the little issues to see about something that might get ready for a build.
@@FromthehamshackwithNJ4Z - Yes! - You just need multiple plates the same and add multiple wires- Please report back! -Cheers!
The next "trick" will to be to make it multi-banded! - One step at a time...
Done in broadcasting all the time here. You will see wires down the side of a tower totally there just to incresse tower circumference. Thanks to skin effect.
Also not uncommon to see the odd Inverted L made from what looks like a wire rope ladder. All done to help with aerial Q.
Interesting!
Hello Callum. On my DX Commander, (which i love!) I got an improved tune and Q on the 40m wire by putting a little 2 inch spreader about 6 inches from the top eyelit. i suspect there was a change in the capacitive coupling at the top of the wire by spreading out the fold-over. KC1PHY
Interesting.
pe1rzd 's view.
The aluminium ring (connected to wire's) makes it huge and not a thin wire.
Metal underground under it make's influence.
Just my 2 cents
Take a look at the woodpecker dipoles for 4+ MHz
I would not "stagger tune" the elements, just a suggestion, but maybe use the bottom sections and plates from one of your existing antennas and put 6 identical 10m elements on it. the resonant frequency will drop a bit but the bandwidth should be much greater. It has been 40 years since I got to play with a cage dipole (At Cable and Wireless at Porthcurno). The cage dipole far ends converged back into one as you described but I am sure much of that is for mechanical simplicity. In theory by sharing the current between multiple conductors the losses will be reduced. I vaguely remember that the cage dipoles had huge bandwidth but it was a very long time ago. A while back I did mess about with a MMANA model of the 6 elements for 10m all cut the same and it did look promising... scaling for 80m might get a bit ugly though....
Yes.. So last night I quickly modelled 6 vertical radiators for 80, Tha bandwidth was BIG but when I tapered the ends, it reduced. Fascinating.
@@DXCommanderHQ it is worth sketching out what is going on "whiteboard style".
The antenna wire itself is an inductor, it couples capacitively to "free space" via capacitance, free space itself is the resistive component. Some of what you are modelling suggests to me that you have a capacity hat effect going on. I believe that only the top (high voltage point) of the antenna needs to be "fat".
With the weather we have at the moment maybe you could solder a coax to a biscuit tin and do some playing with a 2m or 70cm model, I did exactly that years ago. Even did a fat folded monopole...
Surface area helps with bandwidth.
Tinfoil Helmets.... Capacity Hats do provide a small increase in banwidth, but I have not seen a definitive treatise on where to site them on the element.
My Hustler 5BTV has it below the 80m trap, but I have seen them sited a short distance from the end of a full size wire element.
Over long elements can be brought to resonance by use of a capacitor (variable) at the base of a radiating element.
My brain hurtz lol.
The only time I've seen a capacity hat working well is to push say an 80m vertical down to 160m.. Physically, it just looks like 4 x Inverted Ls..
I've modeled and built fan dipoles with slightly different length wires with dismal results (my error I'm sure). How about a vertical made of twin lead shorted at both ends? Effective radiator of 1" diameter. The "Sleeve coupled resonator" is an interesting concept as well.
That sounds also like an experiment..
th-cam.com/video/fBdcyQvu3jM/w-d-xo.html
Kevin Loughlin tried this for a 6m antenna.
Hmmm... could monoband caged DX Commanders be in the future? 🤣
John you can build a great contest station for 10k$ it’s not going to be new beams but classics that perform well at 100 plus feet. 80m vertical loops work well across the band but so do coaxial dipoles. Thick like I like my women 😂
Agreed, I have a friend that has a great contest (little pistol) and DX station that is all wire antennas, and he is a contender in most contests.
@@FromthehamshackwithNJ4Z will you be doing the dx contest this weekend John ?
@@JayN4GO not this weekend have some family stuff going on, but I will be running with a multi 2 for SSB Dx.
Would a massive motorized telescopic antenna also solve this problem?
Yes.. but slightly defeats economy / simlicity :)
What about using a variable capacitor with a stepper motor? 2E1EOZ bob
All would work, I am sure..
6 minutes ago, 42 views!
"I could do 6 or 7 inches" - ok.
I'm going to try a 160m end fed with a thin wire. I'll let you know how it goes. I will only do it if I can get permission from all my neighbours to run the wire around the close!