Electrical Engineers and Antenna Gurus

[KG4CGC]

I have a couple of rolls of flat ribbon cable. Spacing between each conductor is about a millimeter and the conductor itself is about 1.5mm wide. The ribbon is about 3 inches wide and there are a total of 30 conductors. Now then, let's say I pulled off a length of about 30 feet and connected the conductors alternately at each end to make it one single conductor.
Would this act like a coil or a capacitor or just what should I expect to actually happen if I used it at the base, center or end of a wire antenna. Keep in mind it is a receive only antenna I'm talking about and I was thinking of using it as part of an AMBCB and Long Wave antenna.
I do plan on NOT coiling the form. I just intend to stretch it out. I may coil it long ways around a PVC or fiberglass pole if need be but I doubt that will happen. I really would rather hang it in the air.
Thanks in advance. I am without a clue as to the actual outcome. ☺

[ab1ga]

My wild guess is that, depending on the operating frequency, it will act as a slow-wave circuit (delay line). It will look like a piece of transmission line, with the terminal impedance changing with frequency and length, and it can be either inductive or capacitive.

73,

.dale.

[NQ6U]

Interesting, Charles. My own WAG is roughly the same as Dale's but I think it would be more capacitive than inductive. If you coiled it around a pole, though, that would probably increase the inductance significantly.

Try it both ways, put an antenna analyzer on it and see what you get; you never know, it might be a good way to get a low band antenna in a small package. After all, a lot of the antennas we use now were invented by some ham saying to himself "I wonder what would happen if I do this..."

[N1LAF]

Charles, my field of study is not antennas, but it sounds like you are constructing a linear-loaded antenna, where in a dipole form, the antenna is short, because of the zig-zag connections on each side.

From: http://www.qsl.net/pa3hbb/ll.htm
What is Linear Loading and How Does it Work?

Linear loading is a radio term for folding a portion of the antenna back against itself, in order to reduce the overall length of a quarter wave antenna to a more manageable size. In all the examples I explored, using this technique, the overall length can be reduced to up to 40% of the original quarter wavelength size without the losses resulting from using a loading coil.

From a mechanical point of view, the antenna can be made from either a single length of lightweight tubing or from a number of length of telescoping tubing, and it can be self standing. There is no weak point from the insertion of a loading coil into the radiating element and there are no losses from the resistance of a coil. There is also no need for an insulator in the element or a coil former. The weatherproofing of the radiator is much easier and the time to build, set up, and test the antenna is reduced considerably. Mechanically, it makes for a strong stable antenna.

So, how does it work? Well, this is an interesting area of discussion.

Electrically, the antenna looks and acts like a vertical 1/4l radiator but with a different (higher) impedance at the feedpoint. On reception, it works almost as well as a full size radiator over the same groundplane. On transmit it seems to perform equally well, with the same reports being received with either antenna (I also made a 1/4l full size vertical for 40 metres for comparison). The feedpoint impedance is altered by the loading effect of the folded section of the antenna and the top hat assembly, and this requires careful consideration when it comes to resonating the antenna and matching it to the transmitter.

Why a vertical antenna?

As a lot of you will appreciate, to work good DX requires a low angle of radiation from the antenna. It is possible to achieve this low angle with a horizontal antenna, but only if sufficient height above ground can be achieved. Though this is possible on the higher bands, it is nigh on impossible at 40 metres and 80 metres (at least in the majority of UK sites). The vertical antenna looks to be the perfect low angle radiator, except for one thing... the height of a 1/4 l at 80 metres is 20 metres, or 66 feet

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Increased self-coupling (bending back some of the wires) reduces resonant frequency, which reduces the dipole length by 30% to 40%. So, at 1 Mhz, the 1/4 wavelength is 246 feet, multiply by 0.6 will give you 148 feet. For 1/16 wavelength, divide by 4, and you have approximately 36 feet. With the extra overlap at 1/16 wavelength, 30 feet is a good number.

If you want to read more about this, Google with "Antenna linear loaded BCB Listening" should give you good results.

Since you are using it for receive only, and have limited size, it should do OK.

This is an educated guess on my part, for what it is worth...

[PA5COR]

On QRZ in my bio you can find the helical wound 160 metr antenna i started with.
!/2 wave of wire on a pole of glassfiber 1 1/2 inch in size, top capacity loaded.

This antenna you think of would get a lot of wire in a small length, capacity between the wires is quite large so close together, would be nice to keep my MFJ 269 on that if finished and see what it tells us.

The principle of this folded back antenna a few times is already on the market/books, http://www.nonstopsystems.com/radio/...enna_cobra.htm
Like the Cobra lineair loaded dipole.
http://www.nonstopsystems.com/radio/...C_analysis.pdf

Analysis of the Cobra.

[W9WLS]

do a search for the "COBRA ANTENNA" you will find about the same as you are discribing.

[KG4CGC]

Does anyone think it will act as a really long wire for the bands I want to use it for?
Thanks for all the advice so far.

[W1GUH]

Does anyone think it will act as a really long wire for the bands I want to use it for?
Thanks for all the advice so far.

It would be doubtful, if by "long wire" you mean those that are multiple wavelengths long and have gain. For those, the overall length is what counts.

[PA5COR]

Even the Cobra antenna based on the same principle needs a certain length and distance between the wires and number of folding sections to be able to work on the bands designed for,
Getting so many wires so close together in the small place will be very difficult to calculate .
Trial and error, for AM you could try to mimic a Cobra antenna designed for 160 meters, all my 160 meter antenna's give good results on the Braodcast AM band.

That Cobra antenna is already described in the links, is relative short and easy to reproduce.
With the setup materials you have now i think the capacity between the wires and number of wires will make a lousy antenna.
;)

[WØTKX]

You'd probably be able to get a workable SWR by playing around with it.
Likely it would be a dummy load. Oh well.