Audio Amp, Compressor and Noise Gate

A multi-function audio chip controls the audio input to the keyer.

Audio Amplifier:
The microphone input is routed through a high pass filter (HPF) to reduce any low frequency noise or hum that may be present on the audio input. Following the HPF is a single chip amplifier/noise gate/compressor. The audio gain of the amplifier is adjustable from the front panel. The audio level setting can be adjusted to find the proper level to match your type of microphone to the level 
required by the message-recording chip. There is also a 5 V pull-up pin on the microphone socket for those wishing to make use of an electret condenser microphone.

Noise Gate:
The audio chip also contains a "noise gate" feature, used in this unit to reduce background noise. Examples include blower noise and other operators in the same room in a multi-multi contest operation. The level of the noise gate threshold is fully adjustable and a typical reduction of 6 dB in unwanted noise is possible. This feature not only allows for a cleaner-sounding signal on the air but also enables the user to make higher quality voice message recordings. The noise gate can be disabled by a toggle switch on the front panel.

The compressor on the audio chip is also fully adjustable from the front panel and can be switched in and out of the audio circuit with a toggle switch. The compressor can be used in cases where the 
transmitter does not have a compressor or where the output level of a microphone is not able to drive the audio stage of the radio sufficiently. It is not advisable to use the compressor on the Super Combo Keyer as well as a compressor on the radio!

Last updated 15 January 2001 by [email protected]

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