The influence of nearby objects on the operation of the pin and lightning protection. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Civil radio communications

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A radio amateur with a whip antenna can perform a simple but visual experiment. To do this, you need to turn on the transceiver connected to the pin for transmission. Near the whip antenna, using the device (Fig. 1), you can see how your transmitter makes the indicator light up. If the transmitter power is not sufficient to light the LED, connect an RF voltmeter instead.

Rotating this simple probe, you will see that the indicator shines to the maximum when the probe is parallel to the pin and does not shine at all or shines very weakly when the probe is perpendicular to the pin.

Now look at the items located near the pin on the roof. In any wire parallel to the pin, quite significant currents will be induced, which will waste the power of your transmitter.

Often the vertical masts on the roof, which serve as a support for TV antennas or wires for radio, telephone, are stretched with bimetallic or steel wire. At the junctions of oxidized materials, a non-linear effect may appear. In this case, the frequency of your transmitter can be multiplied, added to some other powerful radio signal, and so on.

Since these "contact" semiconductors are exposed to the atmosphere, the non-linear effect (and hence TVI) can be observed, say, in dry weather, or only in damp, or be irregular.

If the vertical masts are located at a distance equal to the height of the pin, then there will still be distortion of the whip antenna radiation pattern.

To eliminate these undesirable effects, the following rules must be observed:

1. It is highly desirable that there are no vertical objects in the zone of the whip antenna, limited by the wavelength.

2. If this is not possible and TBI occurs when working on the pin, then you can try to lower the quality factor of the interfering pins. To do this, it is necessary to paint them with paint mixed with graphite, or rub heavily with graphite. (In cities, at the final stops of trolleybuses, you can often find large pieces of graphite, which are simply thrown away when repairing pantographs). It is necessary to ensure that there is no metal-to-metal contact, and where it is, break it with an insulator.

3. If 1 and 2 are not possible, try to position the whip antenna so that the vertical obstructions are under the shield of counterweights, which is the best solution.

Radio amateurs whose pin is insulated from ground but connected directly or via an inductor to the cable can make a very visual experiment. To do this, in the summer before a thunderstorm or in winter in dry snowy weather, you need to connect the "neon" to the cable coming from your pin. You will see that the light bulb will start flashing intermittently. Now connect a capacitor with a capacity of 200 to 5000 picofarads in parallel with the light bulb (this is the total capacitance of the P-loop). Flashes will become noticeably more powerful, and with a capacitor capacity of 1000 picofarads, a neon can even fail.

Now suppose that such an antenna is connected to the transmitter. If it is transistorized, then the charge accumulated on the capacitors can break through the output transistor. If you have a radio tube with a small anode-cathode gap (GI-7B type) in the RA, then such a charge can burn through it too. Even if this does not happen, high voltage can ruin the P-loop capacitors, especially if they are designed for low voltage.

To prevent this from happening, it is necessary to remove static electricity. To do this, it is necessary to connect the pin with counterweights with a resistor with a resistance of 10 to 100 kOhm, with a power of at least 2 watts. It is desirable to ground the counterweights through such a resistor to the electrical "ground" right on the roof. This will greatly secure your work.

It is not recommended to use the whip antenna during a thunderstorm, as a direct lightning strike is possible, especially if it is higher than other grounded masts.

Author: I. Grigorov (UZ3ZK); Publication: krasnodar.online.ru/hamradio

See other articles Section Civil radio communications.

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