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

What's missing with the initial assumption of Z at the end of a folded dipole is that it relies on the existence of a certain impedance at the feedpoint in the center. If that's shorted then the whole thing becomes a (useless) 1/2 wave stub as mentioned.

A ~300 Ohm resistor could be placed at the original center feedpoint and then the endpoint impedance could probably be matched, but you just end up with a radiating dummy load.

Since useful power would be dissipated by the resistor, it could be replaced with the feedpoint of another antenna with matching Z. Now things are coming off the rails and phase relationships have run amok.

 

So what did you get for a final impedance?

 

Guy is well spoken but boring because he yammers on. He took 13 minutes to cover 5 minutes of material. What he's doing is good, but he should have an outline off camera to follow and "keep moving" in big letters on the sheet. All that said, he's Walter Cronkite compared to most other ham videos.

I learned this by watching some of my own boring videos.

 

If you use a 1:9 unun at the end of a 1/2 lamda, you get an antenne that behaves like a dipole.
So if it is as long as a dipole, behaves as a dipole it might as well be a dipole.. an end-fed dipole.
In many cases it is easier to feed the dipole from the end. It may save coax. Also a vertical dipole is easier to feed from the lower-end. GD DX to all, Math, PA3BUL.

 

If you don't understand basic antenna/transmission line theory but you make a video of it, and QRZ features it on the home page you get a lot of views and spreading of misinformation.
It's a simple 1/2 wavelength of transmission line. The feedpoint impedance is the same as the far end, a short.
Trying to feed a short with a high impedance transformer?
This video either should be removed or a warning in the title that this is 180 degrees out of phase with antenna fundamentals.

 

Ham radio is about experimentation and that's what this video is, a video series on an experiment. He isn't spreading misinformation, he isn't even claiming anything. The first half of the video is just him saying "no idea if this will work why not try it". It's a good educational example of how to think about designing an antenna. Hopefully, he'll make a video explaining what worked and didn't work so others can learn.

 

It's good to experiment

(Couldn't help it)

 

By definition a dipole is defined by function and having no greater than two current nodes with no regard whatsoever to location of the feed point.

From IEEE-100-1984 - ANSI/IEEE Std 100-1984 IEEE Standard Dictionary of Electrical and Electronics Terms

“dipole antenna (antennas). Any one of a class of antennas producing a radiation pattern approximating that of an elementary electric dipole.
NOTE:Common usage considers the dipole antenna to be a metal radiating structure which supports a line current distribution similar to that of a thin straight wire so energized that the current has a node only at each end. Syn: doublet antenna.“​

From IEEE-145-1993 - ANSI/IEEE Std 145-1993 IEEE Standard Definitions of Terms for Antennas

“dipole antenna (antennas). Any one of a class of antennas producing a radiation pattern approximating that of an elementary electric dipole. Syn: doublet antenna.
NOTE: Common usage considers the dipole antenna to be a metal radiating structure which supports a line current distribution similar to that of a thin straight wire so energized that the current has a node only at each end."​

From EIA/TIA-329-B - ANSI/EIA/TIA-329-B-1999 Minimum Standards for Communication Antennas.

“Half-Wave Dipole Antenna. A dipole whose electrical length is half a wavelength and is formed by a straight metallic radiator, one-half wavelength long, whose diameter is small compared to its length, so energized that the current has two nodes, one at each end, producing maximum radiation in the plane normal to its axis."​

Yes.

 

I tend to agree.

I am inclined to NOT "beat him up" for doing what most would call "experimenting". That's how all of us learn......

Now, If he arrives at the wrong conclusion, there will be no shortage of people here to set him straight...........(gently or otherwise)

 

But seriously, to TBT, experimentation is the foundation and very essence of amateur radio so no one should discourage that, although posting a video (compared to posting a comment) will ratchet up the stakes, perhaps higher than necessary.

 

You could learn ten times as much by looking up a shorted half wave transmission line in any antenna book in the last 100 years and realizing what it is, and it isn't an antenna. He has a vna. Let him show the real characteristics of a shorted line, then the viewer will learn something. But calling it an antenna, or experimenting? no, sorry, can't agree.

Say you ran a transmission line out your window to a dummy load in the yard, would you call that an antenna? Would you call it experimenting? No? Ok, then, replace the dummy load with a short circuit. Now are you experimenting, and expecting it is going to magically become a half wave end fed folded dipole super duper antenna? No, it is not.

 

This makes a good topic for an "April Fool's" joke. Nothing more, nothing less. Reminds me a bit too much of the old one about transmitting into two six inch nails, but fed by 132 feet of balanced line feeder !!

 

An end-fed is generally called a marconi. To be a longwire it must be multiple wavelengths long at the frequency of operation, thus an end fed wire worked against ground that is 122 feet long is not a longwire on 75 meters, but it would be considered a longwire on 10 meters.

I am pretty fed up with folks not using the proper names for things. The only possible end fed dipole is a coax or sleeve dipole, but of course the feed point is still in the center, the feedline just happens to go down the center of one dipole element.

What this fellow has is a 1/2 wave folded monopole. He will need matching. I am not sure the impedence, but a 1/4 wave folded monopole has an impedence of 150 ohms and has been in use at vhf and uhf as a base station antenna since at least my 1968 ARRL handbook.

It is sad that those who are inexperienced and do not know any better will take a video like this as truth and start calling things end feed folded dipoles.

Should we start a go-fund-me page to purchase a clue for this fellow, or maybe a good collection of theory books?

 

Experimenting is mostly a good thing.
( Unless in involves puberty or "controlled substance "' )

But it helps to have some idea about the validity of an experiment.
Would you "experiment" in putting 10 pounds of potatoes into five pound bag?
Probably not.

But it seems to be accepted by this crowd to present this "fooled diploe experiment" without apparent knowledge of the size of the potato bag.

73 Shirley