Taurus 80 - User Manual

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HF Receiver Taurus-80

Transceiver “TAURUS”

The QRP transceiver “TAURUS” is designed to operate in SSB on the 80-meter band (3,5…4,0 MHz)

with an output of 4-5 watts. The diagram of the transceiver shown below. The transceiver is splitted to four

independent units: the receiver (RX unit), the transmitter (TX unit), power amplifier (UM unit) and digital

counter (frequency meter with LCD). Each unit can work independently from each other, or can be used with

other transceivers.

Operating of Receiver “TAURUS-80”

Diagram of the Receiver “TAURUS-80” is shown on picture on separate page.

- Two MOSFET: VT1 (J310) and VT2 (J310) are RF Amplifier.

- A core of Receiver is DA1 (МС3362Р): VFO, 1st mixer, IF amplifier, BFO, SSB demodulator.

- AGC is designed on the transistor VT3 (2N3904) and diodes VD2 and VD3 (1N4148).

- The AF amplifier is designed with the popular LM386 (DA2). The output of LM386 is connected

to the speaker 0.25W, 8 Ohm.

- 4x quartz crystal filter is assembled on four crystals Z2-Z5 8.867 MHz. The same crystal Z1 is

used in reference oscillator (BFO), but its frequency is shifted down using the inductor Dr4 and by

trimmer capacitor C40.

- VFO frequency works on 5.070 - 5,370 MHz by tuning of multi-turn potentiometer R8 10-50K and

changing the bias on the varicaps VD4 and VD5.

- The bandwidth of the input bandpass filter at L2,L1 and L3,L4 and the load circuit in the HF

amplifier T1 must be in range 3.5…3.8 MHz.

The PCB dimensions are 130х50 mm. The Receiver is a very easy for assembly and starts working with a

“long wire” antenna just of few meters. The stability of VFO is enough to listen to the stations. After a short

time of warming up, the reception frequency could be changes to ~100Hz for 30 minutes.

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Summary

Details the receiver's core components: RF amplifiers, DA1 IC, AGC, and AF amplifier.

Describes the 4x quartz crystal filter and the VFO frequency range and tuning method.

Covers PCB dimensions, antenna requirements, and reception stability after warm-up.

Provides detailed winding instructions for bandpass filter inductors (L1-L4), VFO inductor (L5), and transformer T1.

Outlines steps for connecting peripherals and performing initial checks before powering the receiver.

Details the calibration process for the VFO frequency range and bandpass filter tuning.

General