10-meter Yagi
Due to low solar activity—and thus a small number of potential stations—we used only a simple antenna, such as a CB vertical, for the 10m band in contests. In the spring, we set up a 4-element Yagi that had been sitting in the basement for a long time. The original owner was satisfied with it (during the solar maximum), but we weren’t very impressed with it. One of our tasks before the next contest was to test this antenna.
The original antenna had a 4-meter boom. The MMANA-GAL program calculated that at 28.5 MHz in free space, the antenna has an impedance of 40 –j2 ohms, a gain of 4.5 dBd, and a front-to-back ratio of just over 10 dB.
Based on G0KSC’s documentation (http://www.g0ksc.co.uk/sc2104s.html), I recalculated this attractive antenna design for the 10-meter band as well. The G0KSC Yagi is a very simple antenna thanks to its direct feed via coaxial cable without a matching network. MMANA-GAL reports the following parameters: impedance 50 + j3 ohms, gain 6.2 dBd, and front-to-back ratio approx. 20 dB. Additionally, the boom is 30 centimeters shorter.
These parameters are already much more interesting than those of the original antenna. The modification involved removing the BetaMatch, shortening the boom, drilling new holes for the element mounts, and adjusting the lengths of the elements. Modifying our Yagi was challenging because the previous owner had shortened the elements too much, so I had to replace the end tubes or extend them with thinner tubing to achieve the desired dimensions. Here are the dimensions of the modified 4-element Yagi antenna:
| Element | Length | Position on the boom |
| Reflector | 5.30 m | 0 m |
| Heater | 5.14 m | 1.29 m |
| D1 | 4.88 m | 1.78 m |
| D2 | 4.66 m | 3.7 m |
After the dimensions were changed, the antenna was measured using an antenna analyzer. The measurement was taken at a height of approximately 5 m using a 3.5-meter-long RG-213 coaxial cable. To minimize the influence of a second antenna nearby, the Yagi was rotated 90° relative to it. Here are the measurement results:
| Frequency | Impedance | PSV |
| 27.8 MHz | 67 + j0 | 1.35 |
| 27.9 MHz | 62 + j0 | 1.26 |
| 28.0 MHz | 59 + j0 | 1.18 |
| 28.1 MHz | 55 + j0 | 1.10 |
| 28.2 MHz | 52 + j0 | 1.06 |
| 28.3 MHz | 50 + j0 | 1.00 |
| 28.4 MHz | 48 + j0 | 1.08 |
| 28.5 MHz | 47 + j0 | 1.09 |
| 28.6 MHz | 47 + j0 | 1.09 |
| 28.7 MHz | 49 + j0 | 1.02 |
| 28.8 MHz | 50 + j0 | 1.00 |
| 28.9 MHz | 54 + j0 | 1.10 |
The imaginary component of the frequency appeared on the analyzer below 27.6 MHz and above 29.2 MHz, increasing rapidly with distance from the center of the band. The antenna is therefore expected to confirm the simulated parameters when operating on the 10-meter band.