6 IC-6 Transistor SW Receiver

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This is a 6 transistor-6 IC dual-conversion superheterodyne receiver with continuous coverage of the Short Wave bands from 5.7 to 18.1 MHz. The receiver demodulates AM broadcast signals only, and has the following features: an FET RF amplifier for good sensitivity with a short wire or telescopic antenna, two Gilbert-cell balanced mixers/oscillators for clean signal conversion, two IF amplifiers with an efficient AGC stage for excellent handling of strong signals, a 4 KHz BW IF filter for high adjacent channel selectivity, a vernier dial coupled to a planetary drive for super smooth tuning, a back-lit DFD to show received frequency, a DFD contrast control adjustable from the outside, and an LED next to the tuning knob to indicate 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: 10"(L) X 5"(W) X 3"(H). Controls from right: antenna gain, tunning, volume and on/off power switch. Red power LED and audio jack are above and below switch respectively. Back-lit digital frequency display with black bezel in the center indicates received frequency. A vernier dial coupled to a reduction drive inside the receiver offers smooth tuning in the crowded bands at night. Green LED left of tuning knob indicates relative signal strength. Black banana jack on top accepts a telescopic antenna, which is more than enough for this sensitive radio to receive the world.


Receiver back. Ground and antenna wires connect to spring connectors on left. 12 volts DC supply connects to RCA jack on far right. Display contrast control is left of RCA jack. Two 5 watt resistors (white) wired in parallel supply power to the display screen and reside outside the case to elliminate heating the VFO frequency determining components.


Receiver inside. The receiver was built "Manhattan style" on a single PCB. 3/16" dia. PCB islands were glued at strategic places on the board and used to connect and hold the components. All ICs plug in sockets while transistors, diodes and passive components were soldered directly to the islands and board. An 8:1 vernier dial coupled to a 6:1 planetary reduction drive offer a tuning reduction of 48:1, requiring 24 rotations of the tuning knob to cover the full range of the receiver. Dual-gang tuning capacitor is on the left. Digital frequency display is bottom center, display contrast potentiometer is top right.


The back-lit digitial frequency display (DFD1A) was obtained from AADE (Almost All Digital Electronics). I wired the display in subtracting mode since the VFO frequency is higher than the received frequency. Two 100 Ohm/5 watt resistors wired in parallel outside the case supply 160 mA to the display light, which is more than enough for compfortable viewing in all lighting conditions. A black plastic bezel from AADE trims off the display.


A single-sided PC board between the digital frequency display (DFD) and receiver board was enough to shield the receiver and elliminate interference from the DFD. Red wires (left) connect to a potentiometer with knob outside the case to adjust display contast from the outside. Modified terminal strips and aluminum standoffs were used to firmly attach the DFD to the case.


Signals at the antenna are controlled with a potentiometer and fed to the RF amplifier, which isolates the antenna from the RF tuned circuit. The selected signal is converted by the 1st mixer to a 1st IF of 10.7 Mhz. The VFO feeding the 1st mixer is isolated by a 2-transistor buffer to eliminate frequency pulling of the VFO by the mixer. A crystal filter passes the 10.7 MHz IF signal and eliminates the image frequencies. The signal is amplified by the 1st IF stage and converted again to a lower IF of 455 KHz by a crystal-controlled mixer/oscillator. The converted signal is then filtered by a 4 KHz BW ceramic filter to get high adjacent channel selectivity. A second IF stage amplifies the 455 KHz signal before it is demodulated (detected), filtered and sent to the AF amplifier. A sample from the second IF amplifier is demodulated and amplified by the AGC stage which controls the gain of both IF amplifiers and keeps the volume at a constant level. Another sample from the VFO is amplified and sent to the DFD which subtracts 10.7 MHz and displays the received frequency. An LED at the output of the AGC amplifier indicates relative signal strength.

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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