ZSS Feed

A subject of great interest among survivalists is the BoB, or bug-out bag, the emergency supplies you would carry on your back if you had to evacuate due to a hurricane, earthquake, or zombie attack. They debate long and loud about what should be in your BoB, the best type of BoB to have, and how to carry your BoB. Of particular interest is how to make your BoB as light as possible. You might have to move quickly, and you’ll regret bringing that portable TV if the undead are on your heels. You can even buy a small survival kit in a sardine can at your local sporting goods or camping store.

I have several small items in my BoB that take up virtually zero space and would provide me with the ability to listen to AM and shortwave radio transmissions. With just a tiny diode, resistor, earphone, and some wire, you can build a crystal radio receiver. I keep all of these in a small envelope in my BoB.

Building crystal radios is a popular hobby among radio enthusiasts, and for good reason. These extremely simple radios can be built from just a few small parts. They can be built to listen in on the AM or shortwave bands. And best of all, especially from the survivalist point of view, they do not require any electricity. Crystal radios get their energy from the radio waves themselves.

There are a lot of good commercial radios that run off of multiple power sources, including solar power and hand-cranked power. I have one myself, and I really like it. It even has red flashing lights. But I can’t guarantee that if the zombocalypse comes, I won’t drop it trying to clamber up out the reach of the undead. If I have the following parts (all easily available), I can build a receiver quickly and still listen in:

1 - germanium diode (1N34 type, if you know what that means)
1 - 47,000-ohm resistor
1 - crystal earphone (this must be a crystal earphone; regular earphones won’t work)

It helps if you have a couple of small alligator clips as well, though it’s not essential.

That’s it, as far as what is essential to carry in your BoB. You will need one or two more things when you decide to build the radio. For one thing, wire. I used hookup wire to make the coil shown below. But frequently coils (and antennas) for crystal radios are made from magnet wire, extremely thin wire with an enamel coating. You could easily carry enough magnet wire in your BoB to make the coil and antenna in the same envelope as your detector assembly. It’s in my BoB.

Here’s a diagram of how it’s put together. I’m not going to go into the specifics of how many turns the coil has or how to compute its operating frequency, just give a general description here. If you really decide to put one together, there are great sites like www.midnightscience.com that can give you more exact information. There is an art to building these, so try your hand at one before the zombocalypse occurs.

Wind a coil using half the wire around a non-conducting form like an oatmeal box or a shoebox. As you wind the coil, make taps (small wire loops to which you attach the detector assembly) every few turns. Just make a small wire loop every few turns and burn off the insulation on the tap. One end of the coil gets connected to the antenna. The antenna is the other half of the wire, hung up in a tree or something. (Just stay away from power lines – don’t put antennas anywhere near them. Also, never use such antennas if lightning could occur.) The other end of the coil gets connected to ground, something that conducts electricity and is connected to the Earth. (A cold water pipe works well.) The detector circuit (consisting of the diode, resistor, and crystal earpiece) is attached to the coil using two small alligator clips. Attach one clip (the one connected to the resistor) to the bottom tap (near ground) and the other clip (the one connected to the diode) to one of the taps. Change taps to try different frequencies.

Listen very carefully. The signals are often very faint, since you are only using the energy carried by the radio waves to produce the sound. Usually evening is best.

There are many ways to improve performance, from building a tiny amplifier to
using a variable capacitor to tune frequencies. It depends on how much you want to include. As for me, I’m a minimalist, and space is tight in my BoB. I have the detector assembly already soldered together, as you can see.

Here’s the coil I wound using some hookup wire I had. I wound it on an empty plastic peanut jar. Magnet wire also works fine, but it is a little trickier to wind coils using magnet wire instead of hookup wire like I did here.

All I have to do is clip the detector assembly to the coil, clip the top of the coil to the antenna, and clip the bottom of the coil to ground, and I’m listening. Even if there is no station on the frequency you are listening to, you should still hear a faint hiss that lets you know it is working.

It will never replace my combination radio/flashlight that runs on solar/windup/batteries, but I know that if all I have is my little detector assembly, if I can scrounge some wire wherever I am, I can still monitor radio communications.