Broadband antenna for TV reception
Amateurs-Amateurs have long used in their practice broadband T2FD antenna (Top folder is terminated dipole - loaded at the top the folded dipole) . It is very similar to the classic the folded dipole, the exception is entered in the middle of the top of the load resistor RL, as shown in Fig. 1.
The figure shows that the antenna has a smaller size than the half-wave dipole. It counting on the low frequency channel of television broadcasting, adopted in concrete area. When the load resistance 700 750 Ohms... the input impedance of the antenna is equal to 675 Ohms, so as to align with 75 Ohm feeder use a transformer balun-matching system with TCC transformation ratio 9.
Transformer balun-matching system is performed according to the scheme depicted in Fig. 2, and consists of three RF transformers T1-T3. Their winding wound two wires simultaneously PEV-2 in diameter of 0.5-0.7 mm ferrite rings magnetic permeability WC and an outer diameter of 10-12 mm. They contain ten turns. You can use the so-called "binoculars" - matching device from TV antennas "Taiga" and the like. Those who want to calculate balun-matching system, you can to use the ratios that are listed in [2, 3].
For example, an antenna to receive TV programs with 4-channel meter for the 30-th channel decimetric waves made of copper wire with a diameter of 2.5 mm as presented on Fig. 3. On the plate of one-sided foil fiberglass thickness of 2 mm and dimensions of 130x70 mm cut plots, which solder half of the vibrator, a load resistor, RF transformers balun-matching system and feeder.
Load resistor (power dissipation) resistance 750 Ohm balun-matching system, you should close the lid from dielectric for protection from atmospheric precipitations. To increase rigidity on each half of the vibrator plate set size 48x20 mm sided foil fiberglass, which in the middle of the foil removed and soldered to the edges of half of the vibrator. The cable is secured with two hose clamps. The antenna screws to a wooden mast with four M3 screws. As a rule, in configuring the antenna is not needed.
These antennas were made five copies. They are placed on the roofs of houses. All meter channels and part of the UHF channels are accepted with good quality when the distance to the telecentre 10 km.
Author: A. Ivanov, Tomsk