Antenna & Feeder Line Structure at HPT Faqeerabad:

PAKISTAN BROADCASTING CORPORATION Forums High Power Transmitters FaqirAbad HPT Antenna & Feeder Line Structure at HPT Faqeerabad:

This topic contains 0 replies, has 1 voice, and was last updated by  Ch. Zeshan Yousaf 3 years ago.

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    Ch. Zeshan Yousaf
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    Antenna Feeding and Tuning:

    The current regulation in the antenna and matching of the antenna input impedance to the main feeder surge impedance is achieved by means of sections of concentric wire feeders.

    The surge impedance of the main as well as the tuning feeders is equal to 60 ohms. The main feeder is to be laid parallel to the tuning one. The feeder screens at the section from the antenna base to the point at 210 m are insulated against the ground through rod insulators, forming a current regulation stub relative to the ground.

    The travelling wave conditions in the main feeder are provided by selecting positions of shorting devices on the tuning and main feeders and the bridge between the feeders. The bridge is set in the point of the tuning feeder, where the active component of antenna input admittance calculated according to the tuning feeder length is equal to the inverse value of the surge impedance magnitude of the main feeder.

    The place for the shorting device setting on the tuning feeder is chosen so, that the tuning feeder section from the bridge to the shorting device should repres4nt the susceptance equal in magnitude and opposite in mark to the reactive component of antenna input admittance calculated for the bridge setting point.

    The shorting device on non-operating section of the main feeder is set at a space of 1/4 of operative wavelength from the bridge between the feeders, which is equivalent to the insulator connection.

    The full length of the APPT tuning feeder is assumed to be equal to 300 m, which allows to perform tuning over the whole given wave range.
    The main feeder is made of 12 current carrying wires, dia – 6 mm, arranged over the circumference, dia – 500 mm, and 16 screen wires, dia – 4 mm, arranged over the circumference, dia – 1000 mm.

    The current carrying wires of the main feeder are fixed on insulators with insulation length equal to 300 mm. With such construction, the attenuation in the feeder on the operating wave amounts to 0.02 db for 100 m feeder length.

    The tuning feeder is made of 15 current carrying wires, dia – 6 mm, arranged over the circumference, dia – 800 mm, and 16 screen wires, dia – 4 mm, arranged over the circumference, dia – 1600 mm. the insulation of the tuning feeder, on which high potentials may appear, is performed with the aid of rod armoured insulators with 600 mm insulation length.

    All the feeders are made of bimetallic (steel copper) wires. The feeders suspension is provided on reinforced-concrete supports of special construction fabricated.

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