Since the only equipment that I could afford at the moment is an inexpensive HT about all I can do is change the antenna. That made me decide that I wanted to see what I could build for the radio and I started building a Yagi.
First I started by doing some research looking at 70cm band Yagis. After finding some material regarding suggesting calculations using the wavelength I started making calculations. I had no idea how to make a matching system but plugged away anyway. I eventually came up with the following numbers:
|
Me |
|
Online1 |
|
Online2 |
|
|
Length |
Position |
Length |
Position |
Length |
Position |
| R |
14.78125 |
0.00000 |
13.375 |
0 |
13.5 |
0 |
| DR |
12.62500 |
4.81250 |
13 |
2.5 |
13 |
2.5 |
| DI1 |
11.50000 |
10.34150 |
12.375 |
5.5 |
12.5 |
5.5 |
| DI2 |
11.37500 |
15.56250 |
12 |
11.25 |
12 |
11.5 |
| DI3 |
11.50000 |
20.87500 |
12 |
17.5 |
12 |
17.5 |
| DI4 |
11.37500 |
26.09375 |
11 |
24 |
11 |
24 |
All of the above measurements are in inches and the position is with respect to the reflector. From those numbers I made the the antenna you see to the left. The SWR was an issue though. I decided to try the 4:1 coax balun. Getting a good SWR with this even turned out to be tricky. I ended up just haphazardly trying different connection points for the braid and checking the antenna analyzer. Eventually I tried wrapping the red wire around the driven element as you see in the picture. From this I get below 2.0 for most of the 70cm band with about 1.3 around 446.0-449.0. I have attached this to my BaoFeng UV-5R and hit a repeater 58+ miles on just 4 Watts.
If I were to do this again I would use the YagiCad program again to calculate the Gamma match again and get the parts I needed to do it right. However, this project reinforces the idea that you never know how something will work until you do it.
