First one is an amplifier that is overdriven: Overdriven SSB transmitter operating close to saturation Wrong adjustments of the transmitter can be easily observed like the following pictures show. Then the two audio signals are nearly 100% equal which will result in the demonstrated signal amplitude waveform. The РІР‚СљbalanceРІР‚Сњ of the tone generator circuit must be carefully adjusted to regulate the amplitudes of the two audio signals in a manner that the cross section centering the waveform is as sharp as possible. It resembles an amplitude modulated carrier and should look like this when displayed with an oscilloscope: SSB 2-tone test signal: Transmitter correctly adjusted The heart of the device are two oscillators producing 2 sine waves which generate a new waveform that is formed by superposition of the 2 single signals. IРІР‚в„ўll refer to that in a later page, today we want to talk about the amplitude side only.Р”Р‡irst, hereРІР‚в„ўs the circuit: Wien bridge oszillator used as a two-tone-test generator for checking SSB transmittersРІР‚в„ў linearity If you own a spectrum analyzer with an appropriate resolution the Third Order Intermodulation products (IM3) can also be made visible.

850 Hz and 2200 Hz are a good choice, for example. Also they should have a significant spacing in the audio spectrum. The two frequencies must not be harmonically related and must both fall within the audio passband of the transmitter. The method involves 2 audio tones simultaneously applied to the microphone input of the DUT (device under test). The 2-tone-method is a standarized test method that can be used to determine the maximum output and the amplification characteristics of a sideband transmitter. With 2 transistors and an oscilloscope it is fairly easy to test the linearity of your SSB transmitter.

Test tone generator 177