Broadband helical antenna. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Television antennas
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Commercial television has been widely developed in many large cities. Moreover, transmissions are conducted both in the usual meter range and in the decimeter range. There is a need to use either two different antennas, or one broadband.
In this regard, I want to offer a description of a simple effective television antenna. The proposed cylindrical helical antenna perfectly accepts 5 programs from me in Makhachkala: 3 - on MB and 2 - on UHF. The dimensions were calculated for the decimeter range (700 MHz). The antenna showed visually better quality than a 4-element square, especially considering that it receives all broadcast programs in both bands. At the same time, interference caused by reflection from surrounding buildings has decreased.
Formulas for calculations:
1. Spiral pitch S=0,24L, L[cm]=30000/f[MHz];
2. Coil size D=0,31/L;
3. Turn length l=root((nD)2+S2);
4. Spiral wire diameter (approx.) 0,01L;
5. Screen diameter 0,8NS, N - number of turns;
6. Input resistance Rin=100 Ohm;
7. Distance to screen h=0,2L;
The gain can be approximately calculated by the formula:
Ku[dB]=10lg(15(1/L)2NS/L).
The antenna was made of aluminum wire with a diameter of 4 mm. The larger the wire diameter, the lower the input impedance. Ku \u12d 4dB at 15 turns and 7dV - at XNUMX turns.
The screen was made of aluminum sheet.
Literature
1. A.Z. Fradkin. Antenna-feeder devices. 1977, Moscow.
Author: Yu. Popov (UA6WIA), Makhachkala; Publication: N. Bolshakov, rf.atnn.ru
See other articles Section Television antennas.
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