Diode Switched Audio Limiter

 After messing with the Audio Clipper:

https://wb9kzy.blogspot.com/2023/06/simple-audio-clipper.html

I continued looking at the old QST articles (searching on "limiter")  until I found this one from December 1966 QST:

html version:
https://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/qst/1966/12/page22/index.html

In this article W9NLT presents the idea of using semiconductor diodes to automagically switch in attenuator sections:

Here was his schematic for a buildable circuit:
.

As with the clipper I'd sub the BAT42 for those now unobtanium 1n34s. Essentially the clipper was modified by adding another resistor and then cascading sections to kerchunk in attenuation as the signal increases.  Unlike the clipper the  attenuator doesn't add as much distortion.

I tried this directly from the rig audio but the results were unseen unless the volume was raised to concert hall levels.  So keeping in mind that W9NLT was working with 600 ohm tube gear, I added one of these beauties from Mouser to the circuit:

The TL013 1K:8 transformer boosts the 10 MHz WWV sine wave voltage up by the turns ratio:

input in blue, output in yellow

A 3db attenuator was designed (1000 ohm impedance) and two standard values I had on hand were used: 2700 and 180 ohms (2):

source: https://chemandy.com/calculators/t-attenuator-calculator.htm

Two sections were cascaded for a 6 db (voltage / 2) attenuation:

input from transformer in blue, output after attenuation in yellow

Here is a waveform of the BAT42 schottky diodes being turned on:

input from transformer in blue, bat42 diode clamping waveform in yellow

W9NLT shows up to 10 sections in a row of 2 db attenuators so the next step will be to try maybe 6 or 7 of the 3 db sections ?  We'll see - it does seem promising although not as simple as the clipper.

Best Regards,
Chuck, WB9KZY
http://wb9kzy.com/ham.htm