TuneAid


Posted on Feb 5, 2014

After I built my KN-Q7 kitset 40m QRP single sideband (SSB) transceiver, described elsewhere on this site, I went on to build a matching low power `Z-match` antenna tuner and a sensitive SWR meter. For some reason, I found I needed three hands to tune this apparently simple arrangement One hand to hold the PTT button down, and then two more ha


TuneAid
Click here to download the full size of the above Circuit.

nds to simultaneously adjust the controls on my antenna tuner, while simultaneously whistling into the microphone, after delivering the essential voice station identification, of course! For those new to ham radio, an audio tone or a reasonably continuous level of speech is required into the microphone so an SSB transmitter will generate some RF power. That RF power allows the SWR meter to measure the match between transmitter and antenna, and determine when the antenna tuner is correctly adjusted. My problem didn`t stop with the lack of three hands. A really bad cold had left me with a decided lack of "whistle-power". Those who suffer from asthma can probably appreciate this latter problem all too well. Adding a tone oscillator into the KN-Q7 QRP transceiver would have solved the problem, but space inside that radio is very limited. This external TuneAid oscillator was my solution. The TuneAid is a simple combination of a timer and audio tone oscillator. It`s a 100% discrete parts design, built with common small signal audio PNP and NPN transistors. The circuit diagram is shown in Figure 1. Pressing pushbutton SW1 turns on Q1. This then turns on the oscillator (Q3 and Q4). With C1 initially discharged, Q2 is turned hard on, keeping Q1 turned on after pushbutton SW1 is released. So, only a brief press of the power-on switch is required to start the tone generator. C1 slowly charges through R4, steadily reducing the voltage...




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