Antentop 02 2003 # 003

Igor Grigorov, RK3ZK

The antenna was made by me in one of the hot summer days at the 1998. I was going for weekend to my bungalow and I decided to take my home- brew 80- meters transceiver with myself. I had no antenna for the transceiver. So, I needed to do the antenna, but... I had no time as I have no quality stuff for doing this one. I opened my junk box with old stuff... and... Thirty minutes while I have had a new antenna that served me then several years!

I have done a half wave antenna with "bottle"matching device. Figure 1 shows the antenna. As you can see a wire in long of 40 meters (a half wave antenna) is matched with 50-Ohm output of my transceiver with help of a parallel circuit ("bottle"matching device)- it is L1C1 in Figure 1. Inductor L2 has not electrical connection with antenna circuit. RF energy is transferred only by magnetic field that reduces the level of static interferences at receiving mode. The counterpoise has length of 20 meters of a naked copper wire in diameter of 1.5 millimeters (#14 AWG).

I used a wire from an old burned down electrical transformer 220-V/12-V.

The counterpoise serves both as electrical and radio grounding for the antenna. At operation time of the antenna the counterpoise is placed on the ground in any position (straight or bending). To short static electrical charge from antenna wire to ground is main task of the counterpoise. Not wise to use a long antenna in the field without an electrical ground, because at the first it is unsafe, and in the second, the antenna is very noisy on reception without the electrical grounding.

Figure 2 shows the construction of the matching device. I used a half - liter plastic bottle in diameter 60 millimeters from a mineral water. C1 is attached at a side of the bottle with help of a strong copper wire in diameter of 1 millimeter (#18 AWG). L1 has 15 turns of a copper wire in diameter of 1.5 millimeters (# 14 AWG), length of winding is 70 millimeters.

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