Multi-tap antenna?

Hi all! Please excuse me if this is not the correct forum for this question; I could not find a natural fit for it. Many of the old consoles and even table radios pre-1940 do not have built-in antennas. I'm wondering if I wind can wind a single, long coil of enameled wire onto say, a 10" diameter cardboard form, and tap it at appropriate points for different wavelenths for lower frequencies (say, 150-350 khz), MW, and short-wave bands. For instance, a coil length of 1,640 ft would be 1/4-wave for 150 Khz half-wave for 300 Khz, and full wave at 600 Khz. A tap at 895 ft would provide full-wave at 1100 Khz. A tap at 256 ft. would be 5/8 wave at 2.4 Mhz and (pretty close to) full wave at 4 Mhz. I would add other taps for other frequencies, but you get the idea. In use, I would just connect the lead from the receiver to whichever tap most closely matched the frequency range I was trying to tune in. One end of the coil, of course would serve as the reference, or ground. Does anyone know if this will work? Also, has anyone worked out a good alternative solution? Thank you in advance for any advice! -Dion

Hi. Welcome to the forums. No. most of the early radios that use an external antenna need a long wire stretched out. Least lenghth I would use would be 20 feet.You don't have to earth ground the radio, but, sometimes it makes them work better. I definately wouldn't ground any that do not have a power transformer. They are not safe for that, and, you could at the least cause a mjor shock hazzard.
Hope this helps.
Bill Cahill

You can check on antenna tuner schematics and information using the ARRL antenna book. Amateur antennas use the principle and it works fine, and even HF receivers have different coil taps for the different bands.

Bill and Bill: Thank you for the quick replies. I have the ARRL antenna book, but unfortunately they quickly took the discussion into a mathematical and vector realm that was way over my head. I'm not a dummy, but I could not figure out all of the theory they presented. I will skim that book to see if they ever get around to telling me how to build an AM/SW reception antenna. I will try the long-wire antenna, too, but assume that it is not optimal for a wide range of frequencies. -Dion

Try this;

http://educypedia.karadimov.info/electronics/antennaloop.htm

Actually, it isn't the frequencies. Direction of the wire is very important. Personally, I used to make a four way antenna with wire. It worked quite well.
Bill Cahill

That is a great link, Ron.

The ARRL Radio Amateur's Handbook has more practical information than the antenna book. If you don't have one, check your library.

If you developed the coil and were to use it you have a couple of choices, either directional or non-directional. It should work as a directional by setting it in a horizontal position, or non-directional in a vertical position. I would say experiment with the idea, you can learn more from your experience. Some Manufactures made coils in a wooden frame that set on a pedestal on top of the radio. There were two ideas for making antennas that worked in the house, one was to make the antenna in a box shape.
The other radio concept was to make an antenna similar to the ones used in the 5AA desktop tube radio, where the wire for the antenna was wrapped in a spiral configuration but set on end.
There is another idea that ham radio operators used for receiving, it was too use an antenna tuner at the in-line series of the antenna junction, it was used to balance the antenna to the frequency desired. This was use to accommodate the wrong length of antenna for a different frequency.

If you remember seeing an outside television antenna ( especially the long distance one's,) they had multiple elements and we're actually of different sizes all connected to the same electrical point. That would be the same is taking several lengths of the wire and by using insulators to keep them from touching one another in a horizontal position and yet all being tied to a common electrical point at one end. Any number of frequencies were available and resonance of the antenna was assured.

Another idea was to lay the antenna under the rug or carpet for the radio. Or another, the wire antenna was wrapped around the room by the ceiling, rather than putting in a long wire outside.

NOtt on a radio that wants a wire antenna, and, ground, which is what I think he's talking about.
Bill Cahill

Ron, that looks like a great site! Bill, without getting up to check, I think that all of the radios I have that need an antenna are xfmr sets. One is a Bosch 595 that I just finished restoring, another is a Zenith 12-S-265. There are several others. I may make some smaller, MW-specific antennas for the table radios. I have much studying to do, but this should be fun. Thanks for all of your help! -Dion

From the net:
http://www.mindspring.com/~brucec/coupler.htm

Mr. Ed: Thank you posting the link to the antenna tuner. I think I will put up a long-wire antenna and build this tuner. Another question: Since radio signals are coming at me from all points of the compass, can I erect the long-wire as an "L" or "V" shape in order to catch signals coming from all directions? -Dion

yes you can. just determine what area of the World you are most interested in. Some stations are non directional and others are directed toward one or two specific continents. So for Europe your long wire Antenna ends need to be facing the north to south direction. So the broadside of the antenna would facing East and west.

For an L or V shaped antenna, where the V center is, would be like an arrow point, pointing in the direction that is of no interest. The point of the antenna would point west, if you want to cover both Europe and Africa as an example.

Another type is a slope antenna, But you really need to look at what design best fits your needs. On Older ships and planes the strung longwires. In the 2-30Mhz range on navy ships they used antennas that had loading coils and antenna tuners and couplers that were fed from monopoles.

It seems one question leads to another. What about a box shape, hung horizontally to the ground, of course. I'm doubt I can manage that; I live on a city lot and must use existing supports (trees) to support the wire. But if I coulddo it, would it prove to be multi-directional or omni-directional? -Dion

Generally, the only antenna that is not directional is a vertical.

When I was referring to box shape, it was for use in the house of no more than 2-3 feet on a side. essentially a loop antenna.

When I was referring to a box antenna, here's what I was referring to.

RIF: The photo you show is one of the ideas I was considering. I would assume that this design is similar in efficiency to the loop antenna built into the back of table radios? -Dion

Many consoles used a similar antenna mounted on pivots to adjust direction. They were usually disguised in fiber wraps.