Smooth compensation bridge attenuator for a shortwave transceiver. Encyclopedia of radio electronics and electrical engineering
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An attenuator is a device that allows you to introduce a strictly defined attenuation into a signal. As you know, the use of an attenuator in a shortwave transceiver (receiver), especially in the low-frequency bands, improves its dynamic range. Or, to put it more simply, it allows, under conditions of strong interference, to reduce their level below the threshold for the occurrence of intermodulation and blocking distortions in the receiver, but at the same time leave sufficient sensitivity to "pull out" the useful signal you are interested in. Practice shows that there should be several attenuator adjustment steps (up to 5-7) and the step of attenuation introduced by the attenuator is no more than 5 dB, a maximum of 10 dB, since with a larger step it is not always possible to "detune" from interfering interference. That is why for these purposes it is desirable to use a smooth attenuator, which allows, to the maximum extent possible, to ensure the reception of a useful signal under interference conditions. For example, attenuators in simple imported transceivers ("soap dishes") have only one adjustment step of -20 dB.
The proposed attenuator (see Fig.) has good linearity at various signal levels. The control range is limited by the internal capacitance of the broadband transformer and can reach 60 dB, while the maximum attenuation is introduced by the attenuator when the bridge is precisely balanced.
The specified attenuator can also be used to smoothly adjust the transceiver output power level, while maintaining a high signal linearity. Structurally, the attenuator is mounted on the terminals of a variable resistor, which, in turn, is placed in a tinplate screen, and its handle is displayed on the front panel of the transceiver. When using an attenuator as a power regulator, it is connected between the driver (preamplifier) and the power amplifier. The signal to the attenuator must be connected via the RK-50 (RK-75) coaxial cable.
Transformer T1 is wound with 7 turns of PELSHO-0,27 wire, folded three times, on a ferrite ring K 10x6x5 (or K7x4x2) with a permeability M1000NM.
Literature
1. Radio amateur 1993, No. 12, p. 36. G. Gonchar. Whether the attenuator improves the dynamic range.
2. S.G. Bunini, L.P. Yaylenko. Shortwave Ham Radio Handbook. Kyiv "Technique" 1978
3. B.Yu. Belousov. Shortwave transceiver "Rosa"
Author: Viktor Bashkatov (US0IZ), Gorlovka; Publication: N. Bolshakov, rf.atnn.ru
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