I collect and restore AM radios mostly from the 30s and early 40s. I want to build an indoor AM antenna for my work bench and pondering how little I know about AM antennas. I'd appreciate some info on antenna's. Some of my radios have a single antenna connection while others have 2. Normally with a single wire I connect a 10 foot or longer insulated wire of whatever diameter I have handy, usually stranded as opposed to solid and chuck it behind whatever cabinet the radio is on. sometimes I'll wrap the wire around my 4 fingers several times. Then crush the loop and wrap wire around the center a few times tying a knot to hold the show together. Attach one end to the radio antenna screw and toss the wad of wire behind whatever the radio is sitting on. While working on or testing single wire connection radios I just pinch the end of the short wire with my fingers while striking various poses to improve reception. All 3 of these techniques work surprisingly well but I'm tired of the last one So for my homemade indoor antenna I have a few simple questions:

1. What length range provides the best reception? Is there a minimum and or maximum length for AM reception? I've been told the longer the better. Is this true? (Please no "That's what she said jokes.) Is there such a thing as to long or diminishing benefit?

2. What diameter range provides the best reception? All of my radios with internal antennas use very thin copper wire.

3. Does it matter if the wire used is stranded or solid?

4. Does it matter if the wire used is copper or whatever that silver stuff is.

5. Does it matter if the wire used is insulated? I have some radios with very thin bare copper wire isolated, wrapped around a wood frame and other radios where the thin wire is insulated with cloth and wrapped around a cardboard form several times creating an oval loop. The wire loops are touching one another. I tend to use wire insulated with rubber or plastic or whatever that stuff is. The cloth covered wire is probably standard for the time of manufacture. Is the type of insulation important?

6. I'm assuming shielding is a bad idea but maybe to avoid inside local interference areas on an outside antenna?

7. Does it matter what form the wire takes? Coiled, concentric circles, wrapped in a loop and tied together in a knot, wadded up and tossed behind the furniture? I'm thinking about wrapped around nails in a board like string art. The wire would be insulated, touching and crossing over itself all over the place. It would be very long within about a 1 to 2 foot square. Good idea or bad? Does it matter?

8. Is grounding an indoor antenna necessary? I was thinking about grounding the antenna to the ground connection in a 3 prong outlet. Good idea or bad?

I'd really appreciate some simple answers to some or all of these questions. Maybe a tutorial online somewhere? The tutorials I've found are for ham operators and or way to technical for the issues I have.

Maybe a simpler idea is just describe your ideal home made indoor AM antenna.

Sincerely,
A befuddled lover of old radios.

 

The early AM radios for the most part used what we call a loop antenna, a Google of AM loop antennas should give you a start. Next is an AM long wire dipole antenna and it figures that the typical AM radio band in the US is about 500 Kc to 1.6 MHz. Let's call it about 1.0 MHz as the center frequency. Here is an example of how to calculate the length of a long wire dipole antenna. So it really depends on the type antenna you want with a consideration for distance from the station. Just for simple radio testing a simple loop antenna will do fine. We won't get into all of the wavelength data. The links should give you some ideas. If you need or want more information just ask.

Ron

 

1. The basic and simplest antenna for AM/MW is the long wire antenna/aerial.

2. 3. 4. 5. 6. do not apply.

7. As long as possible, 30’ or more, stretched straight and hung horizontally outdoors.

8. Grounding helps, but not the antenna itself. Look up how an antenna for a crystal radio works.

You can couple the signal from the antenna to the radio by creating an RF transformer using two coils wrapped around a cardboard toilet roll.

 

I use a long wire in the attic of the house. Cheap and effective for AM (MW) and SW.
https://www.ebay.com/itm/275498865702

I made one out of hay bailing wire and nails for my granddad to listen to baseball on his old Silvertone tube radio.

 

I really miss those "Full-Toned" Speakers.
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old Silvertone tube radio.

spook - what is that approximate date of that ad. That has to be a very early version of the "radio button" circuit / mechanism.

ak

 

spook - what is that approximate date of that ad. That has to be a very early version of the "radio button" circuit / mechanism.

ak

I think that ad was from the late 30's. His old radio was likely from the 40's.

 

I think that ad was from the late 30's. His old radio was likely from the 40's.

I've been unable to zero in on an exact date but others have posted 1940 or 1941 for the same model.

 

If the radio is battery powered then grounding a ground terminal will be OK. If the radio is mains powered then probably grounding might not cause a problem, maybe. Or it might destroy a few parts, as some radios have one side of the mains on the chassis. That could include an old one with a line cord resistor, and a hot chassis, with several six pin tubes.

 

Yes. Be careful around antique tube radios. Many old radios were designed with the filaments wired in series and connected directly to AC mains. Your chassis could be live depending on which way the AC plug was inserted into the wall outlet.

 

On the farm in Wisconsin where I grew up, there was a single wire (likely stranded steel) AM antenna going from the house roof-line to a tree about 75' away, which gave pretty good AM reception.
It was attached with an insulator and a screen-door spring to absorb any wind movement of the tree.

 

Your chassis could be live

On one old transformer-less, main-powered AM tube radio I worked on, the chassis was connected to the circuit common through a small ceramic capacitor so the chassis was at RF AC ground for shielding of the RF circuits, but there was not enough current through the capacitor to the chassis to be lethal at the main's frequency.

 

Another vote for a simple loop antenna. 100 feet or so of what ever around 2-3 foot box/tube or something. Will be directional but you will be shocked at how good it will do .