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 4 mm in diameter. The larger the wire diameter, the lower the input impedance. Ku \u12d 4 dB with 15 turns and 7 dB - with 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: cxem.net

See other articles Section Television antennas.

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