We use a 9 element Yagi-Uda antenna in our immobile system. The type of gamma-match we built in this antenna is called “modified gamma-match”, which doesn’t include any capacitor in its adjustable circuit. The antenna is connected to the ground station through coax-cable.
Materials:
- PVC pipe (d=20 mm)
- brass pipe (d=5 mm)
- coaxial cable (50 Ohm)
- connector block (max. 6 mm)
- SMA connector
Planning phase:
The dimensions of the antenna were calculated with the Steeman Yagi Antenna Calculator. We got the following results:
| Wavelenght | 345.38 |
| Boom BL | 640.69 mm |
| Gain | 11 dB (approx.) |
| Reflector | Position P 0 mm Length 166.47 mm |
| Dipole | Position P 82.89 mm Length 166.47 mm |
| Director 1 | Position 108.80 mm (P +25.90 mm) Length 156.94 mm |
| Director 2 | Position 170.96 mm (P +62.17 mm) Length 155.43 mm |
| Director 3 | Position 245.22 mm (P +74.26 mm) Length 154.06 mm |
| Director 4 | Position 331.57 mm (P +86.35 mm) Length 152.80 mm |
| Director 5 | Position 428.27 mm (P +96.71 mm) Length 151.66 mm |
| Director 6 | Position 531.89 mm (P +103.61 mm) Length 150.62 mm |
| Director 7 | Position 640.69 mm (P +108.80 mm) Length 149.69 mm |
As it was mentioned, we use a “modified gamma-match”, just like its recommended on Steeman’s website.
Realization phase:
We measured the calculated positions on the PVC pipe. After that the holes had been drilled with drill-press for the best precision.
- The brass rods cut to size had a perfect fit, so they didn’t need to be glued or fixated.
- We cut the PVC pipe between the dipole and the reflector rod, so the dipole wasn’t impossible to reach anymore. With that the gamma-match could be made. It’s seen in
the photos.
The upper rod of the gamma-match is connected to the dipole with a slice of the connector block, which was cut with a saw.
- After the gamma-match was finished, the PVC could be connected again. We used screws for that for the mountability.
- As the last step, we ended the coax-cable with an SMA connector.
Our antenna is ready for action.
Documentation by: Péter Balla
Adapted to the website by: Boldizsár Fazekas
