8
$\begingroup$

How are PL tones (CTSS, et.al.) typically removed from the audio of received VHF FM repeater signals?

Is it done with a fixed high-pass filter? Or a notch, when using a transceiver with the PL tone configured correctly? Or dynamically, by assuming any constant low tone detected is hum to be removed by an auto-adaptive notch?

Or is it sometimes not removed by filtering because the tiny speakers on handheld receivers don't have sufficient low frequency response?

Improve this question
$\endgroup$

1 Answer 1

Reset to default
8
$\begingroup$

I would expect some low-frequency roll-off in the amp and the speaker. You could check by putting headphones on the speaker output.

Wikipedia says that a 300 Hz cutoff high-pass filter is common.

https://en.wikipedia.org/wiki/Continuous_Tone-Coded_Squelch_System

Also, the CTSS tone is injected at a lower level than the voice content, usually 15% of full deviation. That is about 8 dB below full modulation.

Improve this answer
$\endgroup$

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .