Five-band vertical antenna. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / HF antennas

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The shortwave desire is great to have a set of antennas for each wavelength range, but this is not always feasible due to the lack of space and conditions for placing these antennas. We have to compromise and put multi-range.

The author has tested various types of both horizontal and vertical multiband antennas. The most acceptable were vertical antennas. For a long time, a five-band vertical antenna proposed by Yu. Medinets (UB5UG) was operated. The antenna circuit is shown in fig. one.

Ris.1

This antenna is quite well described in the literature [1, 2]. The resonant length of the antenna together with the feed line should be equal to 42,5 m, so the length of the radiating part l1 is determined by the expression (all dimensions in meters) l1=42,5-e(l2+l3), where e is the dielectric constant of the dielectric (for most domestic cables with solid insulation made of stabilized polyethylene e=1,51).

Yu. Medinets recommends that the length of the radiating part and counterweights be taken equal to 8,6 m. The emitter can be made of a tube with a diameter of 15-20 mm and, if necessary, reinforced with one or two tiers of guys. The number of counterweights must be at least four, they are made of a cord or copper wire with a diameter of up to two to three millimeters. Without a noticeable deterioration in the performance of the antenna, a metal roof with sufficient geometric dimensions can be used as a counterweight. The antenna is tuned by changing the length of the segment l3 (according to the recommendation of UB5UG l3 = 2,9 m) according to the minimum SWR in the cable coming from the transmitter in the range on which the most active work is expected. So, when tuning the antenna on the 20-meter band with an SWR of no more than 1,3, on the bands of 10,14 and 40 m, the SWR can reach 2, on the 80-meter band - up to 3-4.

Antenna tests showed that it works quite well on the bands of 10,14 and 20 m, satisfactorily on 40 m (a decrease in the length of the radiator affects) and is not very effective in the range of 80 m (the length of the radiator is short and the SWR is high).

The Czechoslovak shortwave M. Shasek (OK1AMS) also uses this antenna [3]. For those cases where the segment l3 can be placed near the transmitter, it marks the possibility of tuning the antenna on each band by connecting a capacitor (See in Fig. 1). Capacitor capacitance does not exceed 450 pF on the 80-meter band and even less on other bands. It should be noted that there is a voltage antinode at the connection point of the capacitor, so the gap between the plates of the variable capacitor must be at least 1-2 mm (depending on the transmitter power). With this method of tuning, the SWR on each range can be no more than 1,5.

When working in competitions, fulfilling the conditions of various diplomas, successful work on 40 and 80-meter bands is no less important than on higher frequencies. In this regard, the antenna was somewhat modified (see Fig. 2). The length of the emitter l1 is increased to 11,2 m, while the length of the supply line is determined by the expression

which for a cable with e = 1,51 is 20,6 m.

The antenna is installed on the roof of a small two-story house, made of pipes with a diameter of 45 mm, and reinforced with two tiers of guys. The length of counterweights from a cord with a diameter of 1,4 mm is equal to the length of the emitter.

Ris.2

Due to the small distance from the antenna to the transmitter, the use of an additional feeder line was not required. Connecting the feed line directly to the P-loop of the transmitter gave good results, but antenna tuning was difficult due to the fact that with such an antenna feed, it is necessary to provide a voltage antinode at the feed point, which makes matching difficult. In addition, since the antenna is harmonic, higher order harmonic radiation intensity increases with this feeding method.

To eliminate these undesirable phenomena, an antenna unit was made, which is an oscillatory circuit enclosed in a screen and located near the transmitter. The transmitter output via a 75-ohm cable is connected by a P1a switch to a part of the circuit with an input impedance of 75 ohms, which ensures the operation of the feeder in the traveling wave mode with SWR on each of the 5 ranges close to 1. The circuit inductor, consisting of three L1 sections connected in series , L2, L3 is switched by switch P1b.

The first step in tuning the antenna is tuning the antenna circuit with the feeder disconnected from the transmitter. With the help of GIR or GSS with a tube voltmeter, the inductances of the coils are selected for each range at the middle position C2. Rough adjustment of the construction is carried out by selecting turns, fine - by changing the value of the capacitance of capacitor C2. The second stage of tuning is the selection of feeder connection points from the transmitter for each range using an SWR meter of any design.

The final tuning of the antenna is performed according to the maximum readings of the IP2 device, which is weakly connected to the "hot" end of the circuit. As IP1, a high-frequency ammeter with a thermocouple and a measurement limit of 3 a was used. As IP2, a small-sized magnetoelectric device for 5 mA was used. Coil L4 - contains 3 turns of any wire.

The antenna performed well on 40, 20, 14 and 10 meters. It is especially convenient when working with DX, since despite the presence of an additional lobe on the 14 and 10 m bands, the main power is emitted at small angles to the horizon [4]. On the 80-meter band, the antenna works quite satisfactorily.

The use of the antenna unit significantly reduced the level of radiated harmonics. Careful tuning and shielding completely eliminate TV interference. An undeniable advantage is that the antenna is tuned at the workplace. The antenna is grounded but direct current and lightning-proof.

Literature:

1. "Radio", 1960, N 9, p. 44.
2. Sheiko V. P. "Antennas for amateur radio stations", ed. DOSAAF, 1962
3. "Amaterske Radio", 1967, N 2, p. 56.
4. X. Meinke and F. Guvdlach, "Radio engineering reference book" (translated from German), volume 1, State Energy Publishing House, 1960

Author: O. Safiullin (UA4PA); Publication: N. Bolshakov, rf.atnn.ru

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