I've been testing a new JT4G beacon source , a single PIC chip generating quadrature audio tones for directly feeding a quad-upconverter. Testing by feeding the tone output directly into the soundcard, running Ver 2.4.0 RC4
In the past, with earlier versions of WSJT-X, the JT4 decoder hasn't always been very happy with pure tones and very high S/N. and would often miss decodes. The situation resolved itself when the S/N was degraded by deliberately adding in noise from an audio noise generator
Now, though, with the latest decoder behaviour with a pure tone input is different. Decoding is always successful - there are no missed decodes - but the frequency estimation and the S/N reported are way-out. I use exactly 1000Hz for tone 0 , but the decoder reports a spread from 914 to 1050 at least, and S/N is reported as -15 or so, when it is really a very high positive value.
Getting the S/N wrong I can understand why it may be happening, with the S/N estimation going off scale with no noise to measure, but the random value of frequency reporting is a new one. Why is this ?
See the attached screen shots