August 29, 2016 at 10:21 am #1130
Ch. Zeshan YousafParticipant
The main requirement to the Antenna of Broadcasting Station is its coverage with high-quality broadcasting service of a territory as great as possible.
Field intensity of broadcasting station at the day-time is determined by the ground wave field intensity, the value of which depends on the radiated power, soil conductivity and operating wavelength. The maximum permissible distance for a quality reception of broadcasting is restricted with the interference level at the reception point.
At night, apart from the ground wave, the space wave, reflected from the ionosphere, arrives at the reception point.
Area of stable reception for the ground wave is usually determined, proceeding from the condition of filed intensity of the ground wave exceeding no less than twice as much that of the space wave. Over the range of 200 to 600 m sharp variation of field intensity (fading) are observed at comparatively small distances from the Broadcasting Station. To extend the stable reception area of the continuous ground wave, it is necessary to employ an antenna with anti-fading properties. Such an antenna has a low radiation level at wide angles to the horizon (50 to 90 degree).
At present a wide dissemination in international practice acquires anti-fading antenna, fabricated in the mode of base-fed self-radiating masts of the order of half an operating wavelength.
For 1000 kW transmitter, a half-wave insulated self-radiating mast 273 m high is provided for, designed for frequency range of 525 to 1605 kHz (580 to 187 m) to operate on full power over the whole range mentioned at 100% modulation.
Rather than a narrow range within which the antenna possesses anti-fading properties is an essential demerit of the base-fed self-radiating mast. Its anti-fading range makes about +-5% of the operating frequency.
To ensure anti-fading conditions over a wide wave range, an APPT type, regulated current-distribution antenna has been developed and utilized in the Soviet Union.
Taking into account the above, the antenna type APPT has been designed for the Broadcasting Station in Faqeerabad instead of the base-fed antenna.
The APPT antenna height has been chosen equal to 257 m. With such height, the antenna ensures the operation at waves 200 to 600 m. The anti-fading range is 240 m to 600 m.
The chosen antenna has a lower surge impedance than that of base-fed self-radiating mast, which reduces potentials on its body and facilitates insulation.
- This topic was modified 3 years ago by Ch. Zeshan Yousaf.
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