Circular dish irradiator for 23cm

When looking for the optimal antenna at 23cm, we decided to try a smaller dish with f / D 0,4. The advantage is the simple construction and good availability of materials. The gain depends on the geometric dimensions of the parabolic mirror. We used only an 85cm round dish. Nevertheless, the results were good.

Find a suitable irradiator for a dish with such a focal ratio (f/D 0,4) turned out to be a hard nut to crack. The irradiator itself covers part of the mirror and thus reduces the gain. With a small dish, this effect is quite significant with commonly used irradiators. The solution is an irradiator according to DL4MEA.

The radiator consists of a full-wave loop (quad) in front of a reflector with a diameter of lamda / 2 at a distance of lambda / 8. I intentionally do not state the dimensions in millimeters, because the irradiator can be calculated on the frequency of need.

The construction is clear from the pictures. The reflector forms a circle of one-sided cuprextite with handles. A hole for the N-connector is drilled in the reflector (female on cable). A piece of 50-ohm coaxial protrudes from it, on which the solder ring made of copper wire is soldered (average 1,5 mm). Bending into a circle is easy: mark the required length on the blanked wire and twist it through a pipe of smaller diameter (the wire springs up when released). Use pliers to cut the ring on the mark and fly it to the coaxial. To increase the mechanical stability, we used a support post made of Teflon (dielectric coax cable) opposite the connector. The post is bolted to the reflector from below. Finally, we sprayed the irradiator with several coats of clear lacquer.

DL4MEA recommends setting the radiator to the minimum PSV (supposedly achievable 1,1) just by changing the size of the radiator - reflector. We didn't do that, but when comparing the parabola with DL7KM (approx. 7dBd) the dish came out as a clear winner. It is also noticeable that the dish is covered by an irradiator. When directed directly, the signal is slightly weaker, as when the dish is a few degrees away. At approx. 1,5In performance, we made QSOs at 324km on both sides 59. Who wants better results, it can be viewed over a larger dish, applies, that the larger the area of ​​the mirror, the greater the profit.

Literature:
[1] https://www.qsl.net/dl4mea/