15 Transistor-4 IC SW Receiver

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The drifting analog VFO is history!

This is a 15 Transistor-4 IC dual-conversion superheterodyne receiver with continuous coverage of the SW bands from 5.7 to 22 MHz. It has a DDS VFO (Direct Digital Synthesis Variable Frequency Oscillator) and a back-lit LCD frequency display for accurate and drift-free tuning. The receiver copies AM broadcasts and SSB (Single Sideband) Radio Amateur signals and has the following features: 4:1 and 9:1 baluns to match long wire antennas, a manualy and AGC controlled hybrid-cascode RF amplifier for good sensitivity with a wire antenna, 2 Gilbert-cell balanced mixers for clean frequency conversion, a hybrid-cascode and IC (Integrated Circuit) IF amplifiers with AGC (Automatic Gain Control) for good strong signal handling, AM and SSB mechanical filters for superior adjacent channel selectivity, an FET (Field effect transistor) AM detector for distortion-free AM reception, a high stability manualy adjusted BFO (Beat Frequency Oscillator) and diode-ring product detector for stable and clean SSB reception, and a signal LED to show relative signal strength. The receiver runs on 12 volts DC and performance is on par with high quality commercial SW receivers.

Receiver schematic


Dimensions: 12"(L) X 7"(D) X 3"(H). Controls from left: Top row: Volume, LSB/USB mode, SSB Mode, LCD display, Display Light, RF Tune and RF Gain. Bottom row: Power On/Off, Slow AGC, Memory Down, Tuning, Memory Up, Memory Call, Narrow Filter, Antenna Off and Balun. Phones jack and signal strength LED are below Volume and LSB/USB controls respectivly. Memory push-buttons are used to adjust functions of the DDS VFO such as IF shift and Tuning step. In SSB mode (HAM/Radio Amateur communications), Slow AGC and Narrow IF filter are switched on. Antenna Off push-button disconnects the antenna so I can peak the RF tuner by ear for maximum static. Balun switch selects between 4:1 and 9:1 baluns to match the long wire antenna.



Receiver back. Ground and Antenna wires connect to the black and red spring terminals. 12 volts DC power supply connects to RCA jack at right. Two 5W resistors (white) wired in parallel supply power to the LCD display screen and reside outside the case to elliminate heating of the BFO (Beat Frequency Oscillator) so it will stabilize faster.



Inside the receiver. Circuitry was built Manhattan style on 4 copper boards. Copper surface was used as a common ground to improve stability. All ICs (Integrated Circuits) plug into IC sockets. DDS VFO is green board at center. RF tuning capacitor can be seen bottom left. The BFO (Beat Frequency Oscillator) which is active only during SSB reception is on the bottom right. BFO variable capacitor is below BFO board. LCD display was attached to receiver case with aluminum standoffs and modified terminal strips.



Listening to Radio Amateur SSB (Single Sideband) stations on 20m (14.1-14.4 mHz) transmitting in USB (Upper Sideband) mode. These transmissions are intermittent and closely spaced, so slow AGC (Automatic gain control) and narrow IF (Intermediate Frequency) filter are switched on.



My cat Misty was helping out! Here she was telling me the 12V power supply isn't connected to the receiver :)


A short history | My radio background | Homemade radios | Tube radios
Transistor radios | World band radios | Kit radios | Reel tape recorders
My other interests | Pictures of Lebanon | Radio links
Home | Showcase | About this site

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