One way to create circular polarization is to place both horizontal and vertical antennas on a common boom and feed them through a suitable combiner.
Described satellite the antenna with circular polarization consists of two 3-element DK7ZB antennas with an impedance of 50 ohm connected by lambda/4 coaxial cables giving again an impedance of 50 ohm at the point of connection.
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Antenna construction
The construction of the antenna is very simple and fast if professional element handles are used. A 15 x 15 mm boom and elements (except for the emitter) of 4 mm AlMg rods, which are sold in hardware stores as electrodes for welding machines, were used.
At home, we can make handles for elements in two ways:
1. Shape a piece of PVC (15 mm wide, approx. 30 mm long) above the flame using a piece of pipe so that a pressure clip is formed. On one side, we drill a hole for the pressure screw, which fixes the element in position. Stripping the element from the boom is achieved by winding several turns of insulating tape in the middle of the element.
2. We need insulating material for this - a block with sides of 15 x 15 x 40 mm. We drill two holes for screws on the edges from above, we drill a hole for the element from the side in the middle. Saw the block in half lengthwise. After screwing to the boom, the element is tightly clamped in the handle.
There are other ways to mount the antenna elements in isolation. In my case, I used professional grips. Insulation tape is wound in the middle of the element and the element is pressed into the holder.
Spacing of elements
| Ref-Rad | Rad-Dir |
| 470mm | 280 mm |
Element lengths, emitter diameter 10mm
| Element diameter | Reflector | Radiator (10mm) | Director |
| 10 mm | 1040mm | 980mm | 860mm |
| 8 mm | 1041 mm | 980mm | 868mm |
| 6 mm | 1041 mm | 980mm | 877mm |
The radiators are made of an AlMg tube with a diameter of 10 mm. The radiator is divided in the middle, the gap is 12 mm. The terminals are for soldering lugs.
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Creating circular polarization
The displacement between the horizontal and vertical antenna on the boom-e for the 2m band is 514 mm. Two 75 ohm coaxial cables of length 3/4 lambda times the shortening factor lead from the radiators to the box in which the antenna connector is located. We measure from the braiding, we shorten the outlets to a minimum. The polarity of coaxial cables is shown in the figure (for RHCP, right-hand polarization). I deliberately do not specify the exact length, 75 ohm is a number of types differing in the shortening factor.
Set of satellite antennas
Since the antenna is relatively short and light, it is fixed at the end of the boom behind the reflector on the T-piece of the light mast. It is 70 cm on the other shoulder DL7KM. Both antennas have a fixed elevation of about 15 degrees. This configuration of fixed elevation low-gain antennas gives better results than working on long gain antennas without elevation, where most orbits bring the satellite to the "dead spot" of the antenna.
The antenna was practically used when working through satellites AO-7 and FO-29. The benefit of circular polarization was evident. For FO-29, however, it is necessary to use a higher transmitter power on the uplink, with AO-7 it is not a problem to hear the signal on the downlink even with QRP to this antenna. PSV is below 1.4 in the entire 2m band.