Ham Radio - An end fed folded dipole experiment. Part 1, the idea and design.

It's not a folded quarter wave monopole, it's a half wavelength long transmission line. Nope, not even matching is going to work. It's not 150 ohms, 500 ohms, 2000 ohms, 25 ohms, or even 2 ohms. It's a short circuit where it is resonant which is where it was designed to work (same thing as saying it's a half wavelength).

Fellow hams, we have to be careful. There is a ton of misinformation out there. In fact actual myths, things people believe that have no evidence to back them up. They get accepted as facts. I could list dozens here but we would get off track. The point is, Kevin made a video where he described an antenna he planned to build. His theory has misconceptions - they are not debatable - just plain wrong. He means well but he doesn't understand fundamentals. Yet people pile on with congratulations for experimenting, "Oh, great job, looking forward to more videos, experimenting is the foundation of amateur radio, blah, blah"
Any rf engineer, antenna engineer would look at this video and laugh. Folks, this is why people criticize us and use terms like dumbing down, and getting your license from a cracker jack box.

 

"Using a transmission line as an antenna" has been around for a while.

Even coaxial lines can be utilized as an antenna.

Yes, there are ways to end-feed a section of high impedance open wire balanced feedline as a very efficient antenna.

My friends, please consider the lowly small loop antenna.
The small loop antenna might be technically described as a balanced transmission line that is shorted on both ends!
... or one end, depending on how it is set up.

Impedance is a virtue.

 

And, apparently, ignorance is bliss.

 

Are you disputing that experimenting is the foundation of amateur radio?

History is not on your side.

 

A dipole that is end fed and folded is not a dipole. A flute with no holes is not a flute. But if software says it will work??

 

Oh come on, now. I'm saying what he is doing is not experimenting. He's feeding a shorted line with 49:1 stepDOWN transformer. That's not experimenting unless he wants to see how much transmitter power it takes to blow up the ferrite balun, or un-un! Or his finals.

 

Here is something puzzling me - of course it is OT and may get be banned.
Up front , and I have stated this many times - I have no illusions what is the purpose of this site.

Post in "Amateur radio news " has to be blessed by administrators.
Apparently the virtue of the "experiment" post falls in with the purpose of the forum.

Forum administrators are actively involved in preventing scammers to defraud the less aware forum participants
buying and selling their ware.
And I foolishly though that only government "is here to help ".

Yes, amateur radio is still fascinating hobby , irregardless.

73 Shirley

PS
Small loops have a nickname - magnetic loop. Never heard of term "magnetic diploe". Wonder why.

 

I believe the currents in either side of the twin lead will be out of phase. This will cause cancellation of any radiated energy. It might make a good dummy load...

 

Nope, won't even make a good dummy load. In fact it is the worst load you could have for your transmitter, a short circuit with a matching transformer in between that is trying to step DOWN the (theoretical) zero ohms impedance.
The only question is, which will fail first, the transmitter or the unun (matching coil). It's ridiculous.

 

"I am not sure the impedance, but a 1/4 wave folded monopole has an impedance of 150 ohms and has been in use at vhf and uhf as a base station antenna since at least my 1968 ARRL handbook. - WA3YRE"
WA3YRE is correct that a 1/4 wave folded monopole would work, but the half wave will not.
The Bill Orr Radio Handbooks of the 50s and 60s show a 1/4 wave antenna like this for HF,
which is what the author is trying to do the wrong way.
The advantage of the folded arrangement is that the impedance is higher, possibly mitigating the ground loss.
I would encourage the author to give this 1/4 wave configuration a try.
If you cannot erect it at full height, the top portion can be horizontal, like an L antenna, and still be useful.
A variation is also show in Orr's work, the "Multee", a two band version, which fits on a city lot.
Its performance, if properly installed, can be better than similar sized compromise antennas.
https://www.robkalmeijer.nl/technie...ek/hambladen/radcom/1994/11/page62/index.html
The purpose of amateur radio includes experimentation. Don't bash the newbies when they are curious; offer them help.
When experimenting, it is wise to read up on the existing information, to avoid reinventing the wheel.
In this case, a square wheel. A cautionary tale.
73, AB2RA

 

@KB7TBT: This is just a shorted transmission line. The currents in each wire are opposite phase, thus they will cancel eachother and nothing will be radiated. If you "somehow" find a transformer that will feed both wires in-phase, you will need a ground point for the other end of the transformer. And at that point, you re-created the end-fed dipole again because two wires close to each other, having the same current phase, are the same as one wire.

 

Of course, it's possible to use the correct terminology, but you are not! The center fed antenna you refer is sometimes referred to as a "doublet", and it is one of many types of true dipoles. But not all dipoles are doublets. Any half-wave radiator with the ends not connected to each other is a dipole. The term refers not to the connection method but to the current distibution. The current is distributed along its length so that the current is maximum at the center and at opposite polarity at opposite sides of the center, regardless of where is the feed point. Therefore, the origin of the term, "dipole", meaning, "of two polarities" The dipole can be fed anywhere along its length and these conditions will not change. The feed system can be attached anywhere or not attatch ed at all(parasitic feed). A solid piece of wire, rod, or tubing, fed anywhere, bent into any shape, and mounted in any position, is still a dipole. The only thing that is changed by moving the feed point along the dipole is the apparent feed point impedance. The "windom" antenna to which many people refer is actually an off-center-fed dipole. The true windom is a vertical wire antenna using a half wave piece of wire as a top capacitance hat and as a support wire. The only (minor) radiation from the horizontal section is that caused by the slight unbalance introduced by the off-center attachment. The"j-pole" and half wave "zepp" are both classic (and identical) examples of quarter--wave-section matched end fed dipoles. It's all in the books as stated. The books I highly recommend are the ARRL Antenna Book and Walt Maxwell's "and

Respectfully, N8WUR

 

Hmmmm, seem to have an error n my earlier post. The title of Walt Maxwell's book is "Reflections", any edition, and it deals thoroughly and correctly with transmission lines and matching. Edition 3 is available from CQ publishing and is well worth the purchase.

Respectfully, N8WUR

 

I was under the impression that a Windom is fed against ground, and uses a single-wire feeder, not coax. Any variation of an "off-center fed" antenna would not, per my understanding, be, as you say, "in fact, a Windom." There are variants of the Windom known as the Carolina Windom that resemble an OCF, but they use a tuning stub with a choke as part of the feeder (which is coax). The OCF "dipole" I have uses a 4:1 current balun, but does not use a specific length of coax as any sort on intentional radiating stub.

Also, I am under the impression that a there are more variants to the end fed than you allow...an end fed does not have to be one or the other -random or longwire. There is also the end-fed half wave, which is a specific length and cut to a half wave, using a 49:1 transformer; it is neither a random or long wire. There is also the Inverted L.

Aside from that, I do agree...I am not a fan of the term "end-fed dipole."

 

With all due respect to Artie Johnson, "Veddy in-ter-esting."
You are saying the vertical wire isn't really a single wire feedline for a halfwave antenna, but rather a Marconi-style vertical antenna with an unsymmetrical top section? Hmmmmmm....... we just might have to put this into 4NEC2 and take a look.
Now we are getting somewhere as far as experimenting, and possibly learning something, right N1BCG?