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Encyclopedia of radio electronics and electrical engineering / Television antennas

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It happens that when you come to rest with a tent in the forest or on the river bank, you find that the portable TV does not work well for the standard antenna due to a weak signal. Then experiments with different surrogate antennas begin. The piece of wire found is placed in different places, bent with all sorts of loops. But it does almost nothing. And to make a more or less decent antenna, you need tools, materials and fasteners. But it turns out that the Loop Wave Channel antenna can be quickly made from a single piece of wire, without any fasteners, simply by twisting it. Figure 1 shows the antenna sweep (wire twist), which is then bent (side view is shown in Figure 2).

Fig.1. Antenna sweep

Fig.2. Side view

For optimal reception, a wire with minimal resistance should be used, and all antenna sizes for a particular channel should be taken from the handbook. Since at the resting place, most likely, there is no thick copper wire and a radio amateur's handbook, you will have to limit yourself to "medium-ceiling" dimensions. Any wire found is suitable for the antenna, even iron, as long as it is twisted, and the fabricated structure was rigid enough and did not bend under its own weight and in the wind.

For example, an antenna consisting of 4 frames with a side length of 10 cm will work quite well if it is made of iron wire 00,6 mm or more. The wire is bent in half, and the bend is made in the form of a square 1 with a side length equal to half the wavelength of the received signal. In the middle of the side of the frame 1, closest to the ends of the wire, 2 ends of the wire are twisted at a length equal to a third of the wavelength. Then the same frame 3 is bent again, and then the same twist 4. After completing the frames and twists along the entire length of the wire, the ends of the wire are bent in the form of a rectangle 5 half-wave length, and a width equal to a quarter of the side of square 1. This is a matching transformer, it is located in the middle of the side of the last square 6 opposite the twist 7. At the same time, the ends of the wire must still remain to make a round loop 8 with a diameter of 8 mm (such a diameter of the annular contact of the antenna socket of the TV), separated from the transformer 5 by a short twist 9 about 2 turns. Loop 8 ends with another twist of the same 10. The excess wire must be broken off, leaving the ends 11 about 2 cm long, used to mount the antenna on the TV.

If you place the planes of the frames against each other at a distance of a quarter of the wavelength, bending the twists 2, 4, 7 with an arc for this (as shown in Fig. 2), then you get the antenna "Frame wave channel".

To connect the antenna to the TV, you need a tube 12 with a diameter of 8 mm, twisted from tin from a tin can, stripped of enamel. The length of the tube is such that a manufactured antenna can be put on its end with a contact loop 8. The ends 11 of the wire abut against the TV case. Due to this and the tight fit of the loop 8 on the tube 12, the antenna is mounted on the TV. The length of the ends 11 must be sufficient for this fastening to be sufficiently secure. The end of the wire 13, stripped of insulation, wound with two turns on one arm of the transformer 5, is inserted into the central contact of the antenna jack of the TV. The other end of the wire 13, stripped of insulation, is screwed to the other arm of the transformer 5 at the point 14 of its transition towards frame 6.

If the frequency of the received signal, and therefore the wavelength, is unknown, then they can be approximately determined by the location on the TV of the arrow for smooth adjustment of the frequency of the received signal. The decimeter range starts with channel 21, in which the signal has a frequency of 470 MHz and a wavelength of 64 cm, and ends with channel 60 with a frequency of 790 MHz and a wavelength of 38 cm.

The margin for the length of the twists 2, 4, 7, fastening the frames to each other, is necessary to select the dimensions of the frames in order to improve signal reception. If necessary, you can unwind the extreme sections of the twists and, due to the released wire, increase the size of the frames. Conversely, an increase in the length of the twists leads to a decrease in the size of the frames. If the antenna socket on the TV is located vertically or at an angle, then the twist 9 can be bent accordingly, and if this is not enough, then the transformer 5.

The described design can be used as an indoor antenna by making it from thick copper wire in compliance with the optimal dimensions. The number of frames - the more the better (within 10 pieces).

Author: V. Solonin, Konotop; Publication: radioradar.net

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