Category Archives: Castlemakers Kids

Building Antennas

coax cable antenna making
George (KB9RZQ) showing a finished antenna to the group.

For the June Castlemakers Kids meeting we built an emergency radio antenna out of coax cable.  Since it was ARRL’s Field Day, an annual ‘dust off the radios & get on the air’ event, we relocated our meeting to Putnam County’s Emergency Operations Center (EOC), where some local amateur radio operators were seeing how many radio contacts they could make. It also gave everyone a chance to see amateur radio operators making on air radio contacts and then try out the built antennas.

Testing a newly built antenna in the parking lot.
Testing a newly built antenna in the parking lot.

The design uses a short piece of coax cable with a connector on the end, you can see the instruction sheet we made and an example antenna. It’s a simple design that works quite well by cutting a different cable length for different transmission frequencies. Just strip the wire and twist the coax braid then you’re done. The antennas were then hooked up to a radio, and with a licensed radio operator supervision, they tried their antenna, some inside the building and others in the parking lot, to talk to each other.

Of course making antennas and watching radio operators ‘work the grid’ raised lots of questions. Thanks to George Edenfield (KB9RZQ) and the rest of the PCAUXComm crew for hosting us. And special thanks to Dave Costin for giving us a behind the scenes tour of the Putnam County EOC – lot going on there many  don’t realize.

Stealing Joules

The instructions & a few of the 'thiefs' we made to test out the circuit.
The instructions & a few of the ‘thiefs’ we made to test out the circuit.

This last Sunday, for our first Castlemakers Kids meeting of the year, eight kids (and a few adults) learned about the electronic circuit called the “Joule Thief.” It’s a fun circuit that has gained some popularity in hacker circles, yet a lot of people don’t know about. Two factors make it a good kids project: The simplicity of the circuit and you don’t need to understand the electronics behind it. For inquiring minds it can challenging because it’s not immediately obvious how it works.

A group of the girls at the meeting assemble the parts mostly scavenged from other electronics.
A group of the girls at the meeting assemble the parts mostly scavenged from other electronics.

The name is based on getting extra energy (joules) out of dead batteries. Or at least batteries that most people think are dead. The circuit, with only 4 components, can use as little as .5 volts from a single dead cell AA battery and boost it up over 3 volts – more than enough to light up a white or blue LED. Even a brand new 1.5 volt AA battery won’t do that! For the more technically minded it’s a simple blocking oscillator (IMHO not an Armstrong since there’s no capacitor) that pulses higher voltage using a inductor, resistor, and a transistor.

There are lots of different ways to make the circuit, which turned out to be part of the fun. We tore apart computer power supplies to get the toroid coils, but also experimented using parts from burned out Compact Fluorescent Light (CFL) bulbs too. We found out the CFL parts worked great & possibly how we’ll do it in the future – although it can be tough to wind the toroid from some of the newer CFL bulbs. One future experiment – the Joule Thief circuit can charge dead rechargeable batteries, another great way to get energy out of supposedly dead batteries!