Example of Bad Audio on JT65A 20m 2013-07-08




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Published on Jul 7, 2013

Please do not over-drive your transmitter by setting your soundcard output level too high. And, check for RF getting back into your audio. Bad audio causes transmitted signal spurs and interference on the transmitted signal for which you are responsible.

http://NW7US.us/jt65a.html is a reference with a how-to guide on setting up your JT65A digital station.

When using any digital mode, for instance in our interest of JT65A operation, it is critical that you do not over-drive your transmitter.

Concerning ALC readings and digital operation: In every case that I am familiar with, any ALC action at all indicates that the processing circuits are dropping back the audio drive so the radio will not be over-driven. This results in a non-linear mode of operation, since the output does not follow the input in a straight line. The output drops off or stays the same, regardless of an increase in the audio signal level -- in other words, *not linear* !

Digital modes require that the radio transmit a linear signal at all times. This translates to the fact that there should never be an ALC indication when you are transmitting! Now, on occasional "twitch" of the indicator is OK, but even that will cause the signal to be wide and the error rate for the other station will go up, and there will be splatter during those times of ALC movement.

So: keep the audio drive settings below that which causes any ALC indication to show, and your transmissions should be clean and pure.

73 de NW7US


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