6 dB co-linear VHF antenna. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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6 dB co-linear VHF antenna. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / VHF antennas

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This vertically polarized VHF antenna, which is not very difficult to repeat, has a gain of 6 dB. The "Slim-Jim" antenna is the most popular but only has a gain of about 1,7 dB. I had problems with my packet radio station and saw the solution in increasing the antenna gain. So now I have a gain of 6 dB on the VHF colinear.

6 dB co-linear VHF antenna

This drawing shows the basic structure. There is nothing new in technology here. My antenna is made from 4mm aluminum rods supported by nylon pieces I found in the kitchen (when my wife was away of course). The length of each element of the antenna and the cable are calculated in half a wave (1030 mm), but the cable is 5 cm longer. The cable is bent so that two parallel conductors are formed with a distance of 5 cm between them. The two radiating vibrators remain straight. All three formed elements (two vibrators and a train) are connected using two blocks cut from nylon.

6 dB co-linear VHF antenna

I did not show the dimensions of the cut out nylon blocks, but only their shape in the first picture. It all depends on the design and dimensions of the wood boom you have. It, of course, could be metal, but I had a piece of a wooden bar on my balcony, which I used. It is only important that it be no shorter than 1/4 wave.

Insert the central latch (boom) first, and then stick all the other elements into the dielectric blocks (they should enter with some effort). The vertical/horizontal holes at the ends of the block must have electrical contact between the vibrators and the cable. I used pieces of ferrous wire for this (it sticks to the magnet) with lead components, which has good contact between the two elements. Copper wire should not be used, as corrosion will form between it and aluminum over time.

The strength of the nylon block is more than enough to support all the elements even in strong winds.

6 dB co-linear VHF antenna

The cable is connected at a distance of 15 cm from the short-circuited end of the loop. The loop is powered by a 50-200 ohm coaxial cable through a balancing transformer. For this, an RG58 or URM76 cable is used. The length of the loop forming the transformer should be 0.33 wavelength. The half-wave radiating element for 145 MHz is 1030 mm, so the length of the coaxial transformer should be about 345 mm (folded in half).

I have recently seen several published articles using this type of antenna, but made from a copper tube. But I think that my method is much simpler and practically costs nothing both in money and in effort (of course, if your wife does not find you in the kitchen cutting off a piece of nylon).

Author: Harry Lythall (SM0VPO), Translated by N. Bolshakov.; Publication: N. Bolshakov, rf.atnn.ru

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