The Can-Can

The Thrifty Rocketeer blog continues...

There are times when two hobbies overlap, or compliment each other.  Today is one of those where rocketry and Amateur Radio combine.

A number of Rocketeers place beepers, egg-timers, or locating beacons in their rockets' nosecones or payload bay to assist in the recovery of rockets that go astray.

Some of these devices require an Amateur Radio license to operate them in the part of the spectrum reserved for Ham Radio. As a result, some Rocketers get a license and buy a cheap Ham Radio to track or "hear" the beeping from a small electronic circuit board in the payload.

But sometimes it is very difficult to determine just which direction to go looking for your rocket.

Let us assume that you have a commercial homing device and you have a hand-held transceiver (HT for short) to hear the signal. Your battery is good, and you know you are on frequency.  You need some method of narrowing the search via a directional antenna or reception.

You can invest in an expensive radio and Yagi antenna, or build a tape measure Yagi from a broken tape measure. (That's a project for another day.) But there's an even cheaper means to narrow the search. 

What you need is an empty Pringles can.

Now, you can paint it, decorate it or do whatever you want to the outside, but it's the metallic foil** properties of the can that you will utilize.  Rinse out the insides and place the SHORT can in front of you, bottom side up.  

As rocketeers, we are all familiar with the term "Through the Wall" construction when it comes to fins.  This is EXACTLY what you are going to do to this can, for only ONE slot.

That is, use a ruler and a sharpie marker or pencil to mark a long thin slot to be cut or sliced through the side of the can. You want the slot to be just about as long as the can is, without slicing either the bottom of the can nor the opening ring.  Keep the slot as straight as possible. Slice with a razor blade or whatever you would use to make a fin slot in a body tube, but ONLY MAKE ONE slot.

Once your narrow slot is finished, use your sharpie marker to draw an arrow on the outside bottom of the can, pointing to the slot. In effect, you're drawing a compass arrow to indicate which way this slot is facing when looking down on the upside-down can.

Most small hand-held transceivers come with a short, flexible antenna, known as a "rubber duckie" for some obscure reason.  You want to hold or place the upside down can over the antenna (and perhaps it will overlap the body of the radio as well).  Your can MIGHT balance on the tip of the rubber duckie and spin slightly.  Or you can hold the can and turn it 360 degrees around.

What you have created is a shield or directional opening so that the HT only receives a signal through that slot. By rotating it, there will be a point where the signal (from your homing beacon) maximizes or peaks.  Turning beyond that will cause the signal to drop off. You might be able to hear the difference in sound level, but most of us can see the signal level on your HT's s- meter.  Just spin the can slowly until you narrow down the direction of the signal. 

The arrow on the top of your can not only points to the direction the slot is facing, but the direction you will want to walk in to search for your homing beacon.

That's it.  The extremely cheap way to create a directional antenna and help recover your rocket, assuming you have both a transmitting beacon and a receiver that you can shield.

Until next time, keep your glue capped and save your scrap balsa!