AM TX low cut filter non-op

[rdwing]

I have recently realized that the low cut TX filter in all AM modes doesn't do anything. It doesn't affect any change on the transmitted signal. However, the high-cut filter does work to control the ultimate bandwidth of your transmitted AM signal.

Is there a certain reason for this behavior, and does your Thetis work like this too? I checked on my Flex too and the TX low cut works properly on that system. This leads to a bit of an unclean carrier if your audio input contains any frequencies down low.

[K1LSB]

Mine also works (rather, doesn't work) as you describe.

Mark

[w-u-2-o]

This question comes up every so often. It is not a bug. It is by design intent, as described on page 87 of the WDSP Guide: https://github.com/TAPR/OpenHPSDR-wdsp/ ... 201.20.pdf.

I remember long ago seeing something from Warren with the rationale for this aspect of the design but unfortunately can't remember the details. Perhaps someone else does?

[K1LSB]

The carrier shouldn't be adversely affected by low frequency audio. I often transmit 4.5k (9k wide) audio on AM and have never had any issue with the transmitted carrier.

Mark

[kc2rgw]

The TX EQ will have an effect.

I just save a separate AM transmit profile with more of the low end reduced in the TX EQ and the carrier level set to 85.