Broadband spiral antenna
In many large cities has received extensive development of commercial television. Moreover, transmission is carried out in the usual meter range and UHF. You need to use a or two different antennas, or one broadband.
In this regard, I want to offer a description of a simple effective TV antenna. The proposed cylindrical helical antenna perfectly takes me in Makhachkala 5 programs: 3 - MB and 2 - on UHF. Sizes were calculated at the UHF band (700 MHz). The antenna showed visually better quality than the 4-element square, especially when you consider that it takes all broadcast programs in both bands. With decreased interference caused by reflection from the surrounding buildings.
Formula for calculation:
1. The pitch of the helix S=0,24 L, L[cm]=30000/f[MHz];
2. The size of the coil D=0,31/L;
3. The length of the coil l=root((пD)2+S2);
4. The diameter of the wire helix of the (approximately) 0.01 to L;
5. Screen diameter of 0.8 NS, N is the number of turns;
6. The input resistance Rin=100 Ohm;
7. Distance to screen h=0.2 L;
The gain can be calculated approximately by the formula:
The antenna was made of aluminum wire with a diameter of 4mm. the larger the wire diameter, the lower the input impedance. Ku=12 dB in the 4 coils and DW - 7 coils.
The screen was made of sheet aluminum.
1. A. Z. Fradkin. Antenna-feeder devices. 1977., Moscow.
Author: Y. Popov (UA6WIA), Makhachkala; Publication: N. Bolshakov, rf.atnn.ru