DK7ZB yagi na 14MHz
In the OM0A contest team, we chose a suitable antenna at 14MHz. Because the workplace is of a portable nature, we considered smaller antennas - 2el.quad, 2the. yagi with direct connection of a 50-ohm power supply, DK7ZB yagi a Moxon. They are all good antennas, but due to the requirement of simple detachable construction and based on good experience with DK7ZB on VHF bands, we chose 2el as the most suitable. DK7ZB yagi.
It is a classic 2el.yagi with impedance 28 ohms and adapting DK7ZB matches from two connected in parallel 75 ohm coaxial cables. The profit is approx. 4dBd, F/B pomer 10dB. The boom is 2.3m long, the longest element is over 11m. The weight of the whole antenna is approx. 10kg.
Dimensions DK7ZB yagi at 20m
| Element (one half) | 35 x 2mm | 30 x 2mm | 25 x 2mm | 20 x 2mm | 16 x 1,5mm | Position |
| Reflector | 0,5m | 1,00m | 1,00m | 1,00m | 2,04m | 0,00m |
| Radiator | 0,5m | 1,00m | 1,00m | 1,00m | 1,63m | 2,30m |
We ordered the material through ALUSET http://aluset.sk/ , small mechanical parts provided by the local hardware store. However, the advantage was, that I had a nylon block, from which the element handles were created. Prisms with dimensions were first cut from the block 100 x 40 x 80mm. A hole with a diameter of 35 mm was drilled into the prisms and two holes for fastening screws perpendicular to it at the edges. Subsequently, the prism was cut transversely. In this way, when the screws are tightened, the oven is firmly held inside.
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The carrier plates are dimensioned 300 x 100 x 8mm. It is necessary to drill the holes for the U-hooks and the screws holding the nylon prisms very precisely. Any inaccuracy has a big effect on the axis of the antenna.
The radiator is divided into two halves. An insulating pin was used due to the lack of nylon, which connects the two pipes. It is beech wood from the handle of the bucket. It's hard enough. It was treated with a thick layer of silicone to prevent moisture penetration.
A waterproof box is screwed on the top of the radiator. It contains the end of the DK7ZB match and the output connector. The conductive connection with the boom is secured by a sheet metal, to which the PL connector is attached. The plate is screwed to the support plate.
Making a DK7ZB match on KV is much easier than on 70cm. I recommend a coarser coaxial without AL foil. At the shortening factor of the coaxial 0,82 a length of 3.60 m is required. At the factor 0,67 it is 2.76m. Distance from cities is measured, where the braid covers the middle conductor. We will reduce the outlets to a minimum. The coaxials are twisted into a circle with a diameter of about 25 cm and fixed with insulating tape above the boom. Especially at higher power, we pay attention to the gap between the coaxial and the boom.
The finished antenna was measured with an antenna analyzer
| Frequency | Impedance | PSV |
| 13,85 MHz | 94 + j0 ohm | 1,89 |
| 13,90 MHz | 87 + j0 ohm | 1,74 |
| 13,95 MHz | 77 + j0 ohm | 1,56 |
| 14,00 MHz | 66 + j0 ohm | 1,33 |
| 14,05 MHz | 63 + j0 ohm | 1,26 |
| 14,10 MHz | 57 + j0 ohm | 1,15 |
| 14,15 MHz | 52 + j0 ohm | 1,05 |
| 14,20 MHz | 50 + j0 ohm | 1,00 |
| 14,25 MHz | 48 + j0 ohm | 1,03 |
| 14,30 MHz | 46 + j0 ohm | 1,06 |
| 14,35 MHz | 45 + j12 ohm | 1,32 |
| 14,40 MHz | 43 + j21 ohm | 1,60 |
| 14,45 MHz | 41 + j26 ohm | 1,88 |
| 14,50 MHz | 40 + j31 ohm | 2,06 |
The measurements were confirmed, that the antenna is set exactly to the band. The antenna behaved very well in the contest. However, despite the relatively wide radiation pattern, it is necessary to target precisely.
The antenna was made for 6 weeks, while the production of insulating prisms took the most time. Net work time is about 20 hours, the cost was about 100EUR.
Recommended information
DK7ZB website
Website www.dxbeam.com – example of professional grip
OM0A contest team
