three-band vertical on the WARC bands

WARC GP, tube

The previous article described a three-band vertical on the WARC bands 10, 18 and 24,9 MHz.

In this article, the vibrator is made of thin wire. Therefore, it has quite high JXa reactances. To compensate for these reactances, a rather complex matching device consisting of three coils and three capacitors was required.

Below is described a similar vertical on WARC bands, but made of a telescopic set of pipes with diameters 40 - 35 - 30 - 25 mm. Because of the greater thickness of the vibrator its JXa reactances are smaller. Therefore, the matching device is simpler. Only two coils and two capacitors.

The antenna and matching device circuit shown in the following figure.

The antenna model is shown in the file 10_18_24.maa. This is a file in the MMANA-GAL modeling program format.

The load w1c simulates the mounting capacitance of the insulator. The last load w8c simulates the loss resistance in a system of radials lying directly on the ground. The system of radials is conventional. At least two resonant quarter-wave radials for each band (preferably four). Ratings of the matching device are designed to install the vertical directly on the ground.

The frequency dependence of VSWR by band is shown in the following three figures.

10,1 MHz band:

18,1 MHz band:

24,9 MHz band:

The minimum in VSWR at 18 and 24 MHz is not exactly in the middle of the respective bands, which is the price for the simple matching device.

The coils of the matching device are frameless coils made of 2 mm copper wire. It is very desirable to measure their inductance before tuning and set it according to the calculation.

During tuning the coils are slightly stretched or compressed. The two capacitors are replaced by small variables for the time of tuning. After tuning, they are replaced with sections of RG-213 cable. From the calculation 1 cm of cable = 1pF.

With proper tuning VSWR antenna in all bands does not exceed 1.3.


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