Enhanced Single Sideband Audio on the ATS-909

Excellent audio is a beautiful thing - especially on the ATS-909!

Looking at the spectrum of incoming signals, as well as the spectrum of your own signal, can reveal the secrets of design and operator skill. There's no place to hide: clean carriers stand out as well as those that are unstable or simply unfiltered. Clicks, pops, buzzes and swishes are all revealed in a waterfall spectral display...

Below are images illustrating both how enhanced single sideband signals can sound as well as the modified ATS-909's ability to deliver excellent audio. If there was one thing I could still change on this receiver, it would be the AGC attack time - it is slow enough to create mild "popping" on strong CW and phone signals. Note that the receiver is stable and its oscillators are clean, with a bandwidth of about 4.5 kHz - perfect for the wider ESSB stations.

Typical signals of the stations with enhanced sideband are clean, stable, and even in spectrum. A few operators tend to have strong spectral lines near 100 Hz - they enjoy the effect of those low bass lines in their speech. One effect that doesn't show well in these spetrograms is the effect of audio amplitude processing prior to enterig the transmitter. Hardly any of these operators use the transmitter's compressor circuit; nor do they allow their signals to activate the ALC circuitry in the RF amplifier stages. That is a key reason for the lack of distortion artifacts near their signals.

Concepts to consider regarding ESSB operation may be found here.