Apache Labs Community Forum

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.

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

Mark

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?

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

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.