High-performance balanced modulator detector
To improve the efficiency of mixers on field-effect transistors in the passive mode is widely used rectangular control pulses. A more effective way to improve the readability, in my opinion, is the use of narrow pulses when the duration of a unit is hundredths and even thousandths of zero duration. (Nicely said, doesn't it ?) At the hearing, it is perceived as the rise of high frequencies. Dramatically increases the intelligibility of the speech signal. Frequency response becomes more uniform. The balanced modulator detector, Fig.1, assembled by well-known scheme A. Pogosova (see the magazine "Radio", No. 10-81).
Fig.1 Balanced modulator-demodulator
The control circuit includes a crystal oscillator assembled on the chip DD1, the frequency divider 4 (Phaser) - MS DD2 and phase discriminator on the MS DD3 and DD4. A square wave signal with a crystal oscillator 1 MHz is supplied to a digital phase shifter (divider 4). With its release removed two anti-phase signal with a frequency of 250 kHz. It is known that in an anti-phase signal there is always some error in the phase difference associated with unstable operation of the phase shifter, and is distinguished by a phase discriminator.
Dedicated phase discriminator signal proportional to the error of the phase shifter, is the reference frequency for the balanced modulator detector, collected on a field-effect transistor VT1. Simultaneously to the second input of the modulator receives the voice signal from the microphone amplifier, when it comes to the transmitting tract. Or the if signal if the circuit is used as a SSB detector (demodulator). Shown in Fig. 1 balanced modulator-demodulator operates at a frequency of 500 kHz and works well at half the frequency of the local oscillator. You can increase the oscillator frequency doubled using a quartz resonator for a frequency of 2 MHz.
The method described above can be offered to try balanced with respect to the frequency converters (mixers) receiving and transmitting equipment replacing chips in the microwave.
Author: M. Sattarov, the Inozemtsevo, Stavropol territory; Publication: N. Bolshakov, rf.atnn.ru