Smooth compensation pavement attenuator for shortwave transceiver

The attenuator is a device that allows you to make a fixed attenuation to the signal. As is known, the use of the attenuator in the short wavelength transceiver (receiver) especially at low-frequency bands improves its dynamic range. Or, simply put, allows in conditions of strong interference to reduce the level below the threshold of occurrence of intermodulation and blocking distortion in the receiver, but at the same time leave sufficient sensitivity to "pull" for You useful signal. Practice shows that the speed of adjustment of the attenuator should be several (5-7) and the insertion step attenuator attenuation is not more than 5 dB, 10 dB, since a larger step is not always possible "to build up" of interfering noise. That's why for these purposes it is desirable to apply a variable attenuator that allows you to the maximum extent possible to ensure the reception of the desired signal under interference. For example, the attenuators in simple import radios (point-and-shoots) have only one degree of adjustment -20 dB.

The proposed attenuator (see Fig.) has good linearity at different signal levels. The adjustment range is limited internal capacity broadband transformer and can reach 60 dB, the maximum attenuation introduced by the attenuator for accurate balancing of the bridge.

The specified attenuator can be used for smooth regulation of the output power of the transceiver, while maintaining high linearity of the signal. Structurally, the attenuator is mounted on the findings of the variable resistor, which in turn is placed in the screen of tin-plate, and its handle is displayed on the front panel of the transceiver. When using the attenuator as power control, he switched between the driver (preamp) and power amplifier. Signal to the attenuator must be suitable for coaxial cable RK-50 (RC-75).

Transformer T1 is wound 7 turns of wire PELSHO-0,27, folded into three sections, on a ferrite ring To 10x6x5 (or CHH) permeability MNM.

Literature

1. Radio Amateurs 1993. No. 12, p. 36. G. Gonchar. Improves whether the attenuator dynamic range.
2. S. G. Bonini.P. Yailenko. Guide shortwave radio. Kiev "Machinery" 1978
3. B. Y. Belousov. Shortwave transceiver "Rosa"

Author: Victor Bashkatov (US0IZ), Gorlovka; Publication: N. Bolshakov, rf.atnn.ru