AM Radio Antenna Booster

While the golden age for AM radio may have been between 1900 to 1950 it can still be surprisingly fun to listen to. AM radio is rich with talk shows with unique personalities and a great way to listen to running commentary on your favorite sport. At night signals can travel hundreds of miles due to atmospheric changes. Hobbyists enjoy the thrill of catching a distance station. Using this AM Radio Antenna Booster, which you will learn to make in this instructible, I was able to listen to a station over 500 miles away. AM radio remains a reliable source of information during emergencies or disasters when other systems may fail.

This AM Radio antenna works by combining a capacitor, along with a large air coil, to fine tune a specific band. This radically boosts the signal of the weak station you are trying to listen to. The antenna creates a "Field" around the antenna and when placed next to your portable AM Radio a significant jump in signal strength is noticed.

Here are some 'novel' features in the antenna's design.:

1. It's mainly made from empty beverage cans.

2. The Frame uses a tensegrity principal - having two floating members.

3. It requires no electricity.

Empty Beer Cans

10' Length of 3/4" wood

PVA glue and some screws

Sheet of Paper

Tape

The stand supports 15 loops of induction wire wrapped around a square wooden stand with 2-foot diagonals.

Here's how the stand is created:

1. Cut 2, two-foot lengths from the 3/4" square timber.
2. Cut 4, 6-inch lengths.
3. Glue and screw the six-inch pieces of wood to each end on the two-foot lengths, creating a couple of 'U' shapes.
4. Support one of the 'U' shape on a bench pointing upwards and supported with some Blue-tac.
5. The other 'U' shape is place over the first. pointing downwards and crosses it in the middle. The ends were supported in a couple of empty beverage cans containing some coins.
6. The two 'U' shapes will be attached together by winding Inductor wire around them. But first, the inductor wire needs to be made, this is explained in the next step.

Inductor wire is created from some empty Beer cans: just remove the top from an empty can and with a pair of scissors, cut a fine spiral of wire.

Insulate the wire using Sellotape. This was done by laying a length of tape from a reel of sellotape on a table with the sticky side up and then placing the wire on top and then folding the tape across the wire, insulating it. Then another section of tape was pulled out, placed on the table and wire laid on it.

Lengths of induction wire from different cans were joined together by sanding the ends for a good electrical contact and then winding together. This wire will pick up Radio Frequency energy transmitted by radio stations. A condenser is then used to select the variable radio frequency energy from the specific radio station you want to listen to.

Wrap 15 loops of inductor wire around the supports. Start from the top and work your way down. Have each loop next to the side of the previous one, they shouldn't be touching each other. Leave a length of inductor wire at either end to allow it to be connected to a Condenser. After a few loops of wire have been wound, the supports become quite ridged.

The idea of using a tensegrity structure to support the loops of wire came about after playing around with a couple of large paper clips, which I had purchased not knowing what I would use them for.

A Variable Capacitor is created using a couple of empty beverage cans one fitted inside the other, separated by a piece of paper. What happens (as I see it) is the electrical charge which has been induced into the inductor wire loop from radio stations transmissions, tries to flow between the two cans but is hindered by the paper insulation separating them. Electrical charge builds up until it is powerful enough to jump the gap and flow to the other side. Then more charge builds up before being strong enough to flow between the two cans. This cycle occurs thousands (k) of times in a second, adjusting how far one can is inserted in the other changes the surface area between the 2 cans and changes the charge required to build up which correlates to a specific radio transmission frequency.

Here how the variable capacitor was made:

1. Make an empty aluminum beverage can more malleable by heating it up over a hot gas flame, I originally did this over a hot top flame in the kitchen but the fumes from the inner plastic coating weren't good, so do this over a gas stove placed outside. I also noticed with one of the cans, the inner plastic coating caught fire and made little pops, so be aware this might occur and try not to burn yourself.
2. Fill the malleable can with water and place in the freezer for 5 hours. The idea if for most of the water to freeze expanding the can but leaving an inner core of water unfrozen. Too much expansion will bust the can or make for too sloppy a fit between cans.
3. Remove the bottom from the expanded can and insert a normal can which has a piece of paper wrapped around it. I used baking paper. Check for a snug fit which still allows the inner can to slide.
4. Attach an end from the inductor wire to each of the cans. I attached them to the can tabs with crocodile clips, but a small bolt and nut could also be used.

With the condenser attached to the inductor, faint radio stations can be listened to using a small transistor radio.

1. Check the transistor radio is on the AM band.
2. Tune it to a faint station on the radio. I found a spot on the dial which made a 'wish, wish' noise but couldn't hear any sound. This tuned out to be a Melbourne radio station over 500 miles away once I had placed the transistor radio next to the Antenna Booster.
3. The Antenna Booster is then tuned to the same radio station's frequency by sliding the two cans together or apart and monitoring the change in the transistor radio's sound.

Top Tips:

1. The Antenna Booster needs to be orientated towards the transmitting radio station with the transistor radio placed at right angles and close to it.
2. Walls can absorb radio waves so use the Booster on the balcony.
3. Distance radio stations are more likely to be picked up at dusk or during the evening due to better ionosphere conditions.

I tried to see if it could be converted to a crystal radio set be adding in a diode and crystal earpiece but couldn't pick up any radio stations. I then tried listening to a mini spark gap transmitter, which worked.