High frequency chokes. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Nodes of amateur radio equipment
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High-frequency chokes with an inductance from several tens of microhenries to units of millihenries are widely used in short-wave receiving and transmitting equipment. If the radio amateur does not have standard chokes with a ferrite magnetic circuit (D-0,1, etc.), then corrective chokes of tube TVs can be used (they are sometimes on sale as spare parts). So in unified black-and-white TVs of the second class there are chokes with an inductance of 39, 95, 140 and 360 μH. Usually they are coils wound in the "universal" way on high-resistance MLT-0,5 resistors (see Fig. 1, a).
Ris.1
These chokes do not have a ferrite magnetic circuit, so they (unlike D-0,1 chokes) can also be used in circuits where relatively large high-frequency voltages operate, for example, in the pre-terminal and even sometimes in the final stages of transmitting equipment. Such chokes are easy to make yourself. On fig. 1, b, for example, shows a self-made choke with an inductance of 330 μH, designed for the printed circuit board of the Radio-76 M2 transceiver (the distance between the holes in the mounting board is 15 mm). The structural dimensions of the throttle are shown in fig. 2.
Ris.2
It is wound on a bar with a section of 3x3 mm, made of sheet organic glass, polystyrene, fiberglass or any other good dielectric. In order not to damage the insulation of the wire, the edges of the bar are rounded off, and so that the turns of the coil do not spread, it is necessary to install cheeks from some kind of dielectric (in Fig. 2 they are shown by a dotted line, and in Fig. 1, b they are completely absent, they were removed after filling the coil with paraffin ). Two pieces of tinned copper wire with a diameter of about 0,8 mm are pressed into the bar - the future ones.
The required number of turns N can be estimated from the approximate formula
N=32root(L/d),
where L is the inductance of the inductor (µH), d is the diameter of the coil frame (mm). For frames with a cross-section in the form of a square, instead of d, the value of 1,2a should be substituted in this formula, where a is the side of the square.
For a choke with an inductance of 330 μH, it is necessary to wind 310 turns with a PEV or PESHO wire with a diameter of 0,1 ... 0,2 mm (type of winding - "bulk"). Indicated in fig. 2, the diameter of the coil corresponds to the wire PEV-2 0,14. Such a choke has a quality factor of about 50 (measured at a frequency of 0,3 MHz).
With an acceptable outer diameter of the coil (about 10 ... 12 mm, like that of a correction choke from a TV - see Fig. 1, a), in this design, chokes with an inductance of up to a few millihenries can be made.
Author: A. Grekov, Moscow; Publication: N. Bolshakov, rf.atnn.ru
See other articles Section Nodes of amateur radio equipment.
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