6 Transistor-6 IC SW Receiver

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This is a 6 transistor-6 IC dual-conversion superheterodyne system with continuous coverage of the Shortwave bands from 5.7 to 18.1 MHz. The receiver demodulates AM broadcast signals only , and has the following features: an RF amplifier for good sensitivity with a short wire antenna, an independent VFO with buffer stage to elliminate VFO pulling by strong signals, 2 Gilbert cell balanced mixers to minimize spurious response, a crystal controlled 2nd oscillator for higher stability, a Collins mechanical filter for excellent adjacent channel selectivity, 2 tuned IF amplifiers with an efficient AGC (automatic gain control) amplifier for high dynamic range, an IF selectivity control to improve AF fidelity, a backlit digital frequency display with contrast control for easy station location, a vernier dial coupled to an internal pulley for smooth tuning, and a backlit signal meter to show relative signal strength. The receiver runs on 12 volts DC and performs as good as or better than portable shortwave receivers on the market.

Receiver schematic


Dimensions: 12"(L) X 7"(D) X 4"(H). Controls from right: antenna gain, tune, display on/off and contrast, volume, bandwidth wide/narrow and power on/off. Signal meter is between display and volume control. Phones jack and power indicator light are below and above power on/off switch respectively. A vernier dial coupled to a large pulley inside the receiver provides very smooth tuning. Ventilation holes on the cover top and sides improve VFO stabilization times.


Receiver back. Antenna & ground compression connectors and antenna attenuation switch are on the left, power supply RCA connector on the right, and my signature and date of production of this receiver at the bottom.


Close-up view of the backlit display. Display's contrast can be adjusted with the contrast control (left) to suit any viewing angle, and the display can be turned off with the on/off switch (right) after a station is correctly tuned in to reduce the receiver's power consumption.


The receiver circuitry was built "Manhattan style" on 3 single-sided PC boards. Large left board contains the VFO and buffer, crystal oscillator, 1st and 2nd mixers, 1st crystal filter, Collins mechanical filter and digital display signal amplifier. Right board contains the 2-stage IF amplifier, AGC detector and amplifier, AM detector and filter, and AF amplifier. Small board on back wall (lower left) contains the RF antenna amplifier. The backlit digital display (top center) was assembled from a kit available from AADE.


Close-up view of the 3 boards. The copper planes were used as a common ground to improve stability. Small PCB islands were glued to the boards to hold and connect the components, and to simplify testing and modification.


The 3 1/8" dia. pulley on the tuning capacitor dictated the height of the receiver case. An 8 to 1 vernier dial is coupled to this pulley through a 1/4" dia. potentiometer shaft and provides a final tuning ratio of 100 to 1, requiring 50 rotations of the tuning knob to cover the tuning range of the receiver. The digital frequency display facing the pulley does not affect reception when stations are correctly tuned in. The tiny bulb wich lights the S-meter can be seen above the black and red wires (lower right).


The receiver tuned to a strong station with the backlit S-meter indicating relative signal strength and giving a nice hi-tech look to the receiver. A mono to stereo adapter allows Walkman stereo headphones to be used with the receiver.


Strong signals that might overload the receiver are reduced to acceptable levels by a resistive PI network before they are sent to the antenna amplifier. Signals are then converted to a 1st IF of 10.7 MHz and passed through a crystal filter to eliminate the image frequencies. A buffer stage isolates the VFO from the first mixer to eliminate VFO pulling by the mixer. The 10.7 MHz signal is then down-converted to a 2nd IF of 455 KHz and passed through a Collins mechanical filter with 5.8 KHz bandwidth to get high adjacent channel selectivity. The signal is then amplified by a 2-stage IF amplifier, detected and filtered before it is sent to the AF amplifier. A sample from the second IF signal is detected and amplified by the AGC stage to show relative signal strength and to control the gain of the IF stages to keep the volume at a constant level. Another sample from the VFO signal is amplified and sent to the digital frequency display which processes it and displays the received frequency.

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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