[600MRG] FT Question Answered?

[Roger Graves]

Interesting that Collins tried using audio tones to generate CW. IDK how they were generating the audio. Now we are using DAC’s. A major problem with these is not that the main audio signal is not stable but that there is wideband noise in addition to the pure tone. SM5BSZ has documented this well and tested lots of soundcards. Some soundcards are so bad that they should never be used for TX. In general, he advises running the TX soundcard at the max bit depth (e.g. 24 bit) and max sampling rate (e.g. 96 kHz) to minimize quantization noise and to run it at close to the maximum output level to maximize the s/n ratio as some of the noise output is independent of the main signal level (this requires using an attenuator or reducing the gain of the transmitter audio input). Further, an audio low pass filter is advisable to reduce the high frequency noise, which can be extreme above the sampling freq in some soundcards. All that noise can be mixed into other frequencies by nonlinear RF stages, so we need to have clean audio for both linear and non-linear amplifiers.