Two antennas for 2 meters. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / VHF antennas
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Portable antenna
The antenna is made of copper wire with a diameter of 2,5 mm and a length of about 45 cm. The L1 coil contains 5,5 turns (5,5 mm pitch). Its inner diameter is 12 mm. A metal "umbrella" is soldered on top of the antenna, which provides it with broadband and reduces radiation resistance. A CP50 connector is soldered to the lower end of the antenna.
The antenna, schematically shown in Fig. 1, designed by radio amateurs W6AAQ and W6TWW for installation in cars. In terms of its parameters, it is close to vertical antennas having a length of 5/8A.
"Pounder"
K1TD, using the theory of log-periodic antennas, designed a four-element antenna, which, due to its low weight (about 500 g), was called Pounder (translated from English means pound). A schematic drawing of this antenna is shown in fig. 2.
The antenna elements are made of duralumin pipes with a diameter of 6 mm, which are attached to the supply line with M4 screws. To adjust from the outside of the elements, it is advisable to provide the possibility of screwing M4 screws about 50 mm long into them.
The supply line is made of two duralumin corners 12x12x1,5 mm, between which there is an insulating gasket (made of organic glass, fluoroplast, etc.) 3 ... 6 mm thick. Between themselves, the corners are fastened on the side of the L4 element with an M4 screw, on the side of L1 - with an RF connector, to which a power coaxial cable is connected. The antenna is attached to the mast using a traverse about 1 m long made of insulating material.
To balance the antenna, the coaxial cable near the connector is wound (six turns) on a ferrite ring.
The antenna has a gain of about 5 dB. SWR at the edges of the operating range is within 1 ... 1,8. The front-to-back radiation ratio is approximately 20 dB.
Author: Georgy Chliyants (UY5XE) Ukraine, Lviv; Publication: cxem.net
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