Shortwave Radio Receiver Plans
SOURCE: MTM Scientific, Inc./ http://www.mtmscientific.com/swradio.html
Presented here are plans for building a shortwave radio receiver using 3 transistors, a simple homemade coil, an air variable capacitor and some common electrical parts. This circuit is from Charles Kitchin, who has provided a multitude of great radio plans to the hobbyist community. A unique feature of this simple circuit is the ability to control the regenerative feedback at the first transistor amplifer stage for high gain. Here we present the circuit diagram with discussion, and describe our compact printed circuit board version of the radio.
The resonant RF front end is tuned using the variable capacitor and small air wound coil. The coil is wound on a 1 inch diameter coil form with 12 turns. The coil is tapped 4 turns from the bottom to provide a regenerative feedback signal. The first transistor comprises the RF amplification stage, and signal regeneration is controlled by adjusting the variable potentiometer. (The trick in using the regeneration is to adjust the gain just short of causing feedback oscillation.) The signal from the RF front end is detected by a 1N34A germanium diode, and amplified by a two stage audio amplifier with two additional transistors.
Here is a view of the compact layout of the printed circuit board. Several convenient features were added in the board layout. The 9V transistor battery is mounted upright using a snap type battery connector, which is soldered directly to the board. The air variable capacitor is also mounted directly to the board. Headphones are easily used with the radio because of the convenient plug type connector. A nice additional feature would have been a low power LED to indicate when power is applied.
The printed circuit layout was done using free designer software from PCB Express. Their electronic schematic and pcb layout software is terrific. Also, PCB Express offers a hobbyist miniboard service which is quick, inexpensive and convenient.
This radio has surprisingly good performance considering it's simplicity. We have found that even a short length of wire strung indoors makes a satisfactory antenna. Many stations were easily tuned inside an apartment building. The nominal tuning range is 5-15 MHz. The tuning range can adusted lower by adding more coil turns, or removing turns for tuning higher. A more substantial outdoor antenna would undoubtedly provide terrific DX reception.
A few comments about using the radio: In today's digital tuning world we've found it great fun to use this radio's analog tuning to quickly sweep the shortwave band with the simple turn of a knob. Also, adjusting the tuning and thereafter tweaking the regenerative feedback for maximum signal requires some skill and practice, which makes our shortwave listening all the more enjoyable.
Shortwave Radio Parts Kit
The SHORTWAVE RADIO PARTS KIT from MTM Scientific is offered in response to numerous requests from customers for help building a radio. This kit contains all the parts needed for a radio, but it does not include any additional instructions. The PCB has the circuit traces, but it does not have a silk screen parts layout. We are offering this kit for advanced electronic hobbyists that enjoy experimenting with radio circuits.
SHORTWAVE RADIO KIT (Catalog #SWRAD)...$44.50, Worldwide Shipping Included!
Ham, CB, SWR, amplitude, frequency, SSB, digital packet radio, FRS, MURS, pirate, etc
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More radio info available at:
The ARRL is the national organization for ham radio operators. I have the TenTec 1253 they mention and it's a decent little radio. Have also built the simple regen that is described in an article mentioned on that page. It does a decent job and is very simple to build.
Shortwave receivers are pretty cheap these days, but knowing you can build one out of parts scrapped from an old television or other piece of "junk" is a good feeling...
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