dullara news Delaware Amateur Radio Association, Delaware OH   VOL 37 NUMBER 4


Craig MIller  W8CR

Convert Your Old Rig into a New SDR, Software Defined Radio

The future is here today.  The era of the superhetrodyne receivers is quickly coming to a close.  The brain-child of famous inventor Edwin Howard Armstrong came to life way back in 1921.  Since then radios have been basically refined versions of the ingenious circuit Mr. Armstrong designed which made an evolutionary leap in radio science by making receivers more selective and sensitive using intermediate frequencies via a mixer circuit. Just shy of 100 years later, a new dawn is here with the advent of Software Defined Radios, SDR for short.  These new apparatus pull signals in from the air and via the magic of high speed electronics, convert the signals into digital data and decoded by computers and software.  Long gone are finely tuned circuits and complicated filters in big boxes with knobs and switches.   This old Heathkit HR-10B receiver was my pride and joy as a novice back in the 70’s.  I built it from a box full of parts carefully following the step-by-step instructions supplied by the fine folks in Benton Harbor, Michigan.  For a novice, this receiver performed well enough, but as years went by, it was replaced by more sophisticated gear with solid state components and digital displays.  This radio has a soft spot in my heart, it’s not worth much on the market but it’s still functional and by no means heading to the scrap bin. The plan is to give this old girl a new life by taking advantage of the new SDR technology while retaining some of the original features of a vintage radio.  I hope to retain the audio amplifier circuits along with the first IF stage that gave this classic the frequency drift we all remember and love.  In essence, this will become a hybrid radio, melding the best of both worlds, yesterday’s and today’s.   Most SDR radios take advantage of clever computer software and high resolution flat panel displays.  I needed a display approximately 3” x 9” to replace the “slide-rule” dial on the radio.  Fortunately, since the kid is at college, the TV in his room was free for the taking.   Another benefit, the TV has all sorts of electronical components that will be repurposed in the new SDR.   The liquid crystal display was extracted with only a screwdriver:   This screen was way too large for my needs so a little re-engineering is required:   Now that the screen is at the proper size, installation of the electronics is next:   Make all of the appropriate connections into the existing analog circuits, mount the screen, we are ready for the smoke test:   Plug the unit in the wall, connect an aerial…   Success!!!  Everything came together perfectly.  Smooth audio with that soothing 60 Hz hum along with the desired wandering drift that today is popularly known as “scanning”.  The high resolution display blends in perfectly with the vintage cabinetry.  The front panel controls are fully functional, no need for a computer mouse to clutter your operating space. An added feature:  during the lull in the sun spot cycle when there are no signals to be found on the amateur radio bands, you can always catch up on classic reruns of Threes Company: