Introduction

While searching the web I came across some cheap yagis HDTV antenna, which claim to operate from 45 to 860MHZ, have a 150 miles  range ( 22-38dB gain) and come with a rotator. All this for for $32.99 including shipping. I wanted to see how well would these antennas work on the 2m/70cm band, and see if I could modify them to work better on these bands.  The particular model I got is the ESky HG-981 from amazon.

Here are the specs for this antennas:

- Frequency: 45-860 MHz
- Gain: 22-38dB
- Rotation: 360°
- Channel: VHF1-12 UHF21-69
- Impedance: 75Ω
- Power: 3W
- Power Supply: AC110V
- Rotation speed: 2-4 rounds/min

Before assembling it, I took it apart and measured everything on it so I can replicate it in an antenna simulator to see what I need to change.

There is only a single coaxial cable leading into the antenna, which contains a filter to pass 12V AC into the motor, and filter out all other higher frequencies into the antenna.

Before going into the radiating elements, the signal goes though another filter (a diplexer) which seems to split VHF and UHF signals into separate radiating elements from the signal feed line.

The VHF radiating element is a folded dipole, while the UHF looks like a dipole with two fingers for radials.

I then reproduces the antenna in Auto-desk Inventor to capture all of its parameters. Here is a PDF file with all the dimensions.

The antenna seem to be composed of a reflector dish for 2M and a yagi for 70cm.