70 cm Yagi Antenna for Direction Finding

70 cm Yagi Antenna for Direction Finding

Every once in a while, we happen to lose something around the Rusty Nail Workshop. In most cases, if we wait a while, it will simply turn up again without us having to look very hard. Unfortunately, that isn’t always the case, and sometimes a better solution is needed.

For example, we are interested in high powered model rocketry. Along with these rockets come very big and powerful rocket engines. Engines powerful enough to cause our rockets to soar to great heights.

Naturally, with even the slightest breeze blowing, the rockets tend to drift on the way down and can often travel large distances over land (a mile or two). If there happens to be a forest or corn field in the rocket’s landing area, finding the rocket can be a very big challenge. This is a problem when some of the rockets start to cost a lot of money and when you’ve invested a lot of time in their paint jobs.

The solution is simple. We need a radio beacon. Everyone should be familiar with tracking collars they place on wolves, bears, and birds. This concept is very similar, except the beacon is small enough to place inside the nose cone of a model rocket. The particular transmitter I purchased came from BigRedBee LLC. The model is their BeeLine TX (not the 100 mW version, since that consumes more battery power and has a shorter life). You need an amateur radio license to use one of these transmitters, but they are not very difficult to obtain. Lucky for us, I happen to have a license!

I needed a 70 cm Yagi antenna to use with this transmitter. Instead of simply buying an antenna, I decided to make one. The plans I followed are as follows.

I purchased the supplies from a local hardware store and put the antenna together in about an hour.

The hardest part was cutting the brass rods, but I used a small cut-off tool with good results. Using a blowtorch to bend the brass really made it a lot easier than simply bending it by hand. Just make sure you use a vice to hold the 13” portion of the driven element to keep it from bending.

I now need to pick up some co-axial cable and a BNC connector for the end. The total cost for this project was about $20.

One final word of warning. After building my antenna, I realized my HT radio (Yaesu Vertex VX-150) was not capable of receiving on the 70 cm band. This means I needed to pick up a new radio. I eventually chose the Yaesu VX-8R.

I purchased a three foot BNC to BNC cable, made of RG-58 from Universal-Radio (part number 4616). I also purchased a BNC to SMA adapter so that I could connect the cable to my Yaesu radio. I then cut one end off of the RG-58 cable, and soldered it to one of the brass rods.

When I finished, it was simply a matter of connecting it to the radio and testing the transmitter. It worked! Now I just need to have the kids hide the transmitter to see if I can find it again.