An audio mute circuit is a device utilized in transceivers (which can be gadgets that each
transmit and receive signals) to quickly silence the audio output. this may be beneficial in
situations where you need to forestall audio transmission for a brief time frame, such as while
adjusting settings or when receiving audio interference.
The audio mute circuit commonly works with the aid of interrupting the audio signal glide while
a transfer is activated or whilst a certain threshold is reached inside the audio enter sign.
this may be carried out the use of diverse styles of components, consisting of transistors,
relays, or op-amps.
whilst the audio sign is muted, the audio output is either silenced absolutely or decreased to
a totally low degree, relying at the design of the circuit. as soon as the mute condition is
cleared, the audio signal is authorized to drift commonly once more.
In precis, an audio mute circuit is a tool that temporarily silences audio output in
transceivers. it’s miles usually activated via a switch or by a positive threshold in the audio
input signal, and it works with the aid of interrupting the audio signal glide the usage of
numerous kinds of components.
The need to install an audio mute circuit was felt by lot of builders who were building the
Bitx version 3 SSB Transcievers a few years back. We present a cicuit that was build by a ham
friend from USA Blake Bartosh.
Om Blake Bartosh has shared with us the explanation as to how the delay circuit works as
you may be eager to try it out on your Bitx.
The Audio Mute circuit operates in the following way. The 555 timer is connected to the PTT
switch and generates a 100 msec pulse when PTT is engaged and another 100 msec pulse when PTT
is released. The 555 timer is configured as a debounce circuit, so contact bounce of the PTT
switch does not initiate any new pulses.
The output of the 555 timer and the PTT switch signal are combined in logic to form two
signals, a mute command and a transmit command.
The mute command turns on Q16 of the Exciter board which shorts the audio signal to ground, and
no sound is heard from the speaker.
The mute command occurs immediately upon engaging PTT, but the transmit command is delayed by
100 msec. This delay ensures audio transients due to switching from receive to transmit mode
do not cause a “pop” in the speaker, but is not so long as to be noticeable to the operator.
The transmit command energizes the relay coil of K2 of the PA board via a 2N3904 transistor and
the rig switches to transmit mode. Upon releasing PTT the transmit command is immediately
turned off, K2’s relay coil is de- energized and the rig reverts to receive mode. 100 msec
later the mute command is turned off and the speaker is activated again.
The Audio Mute circuit is powered by 12V+, and a voltage regulator reduces the 12V+ voltage to
+5VDC required by the 555 timer and the 74LS00 quad NAND gate IC.
The audio mute circuit has been installed in a number of bitx and ubitx ssb transcievers and
can be considered a good project to be build for any transceiver having a thumping sound on
pressing the PTT key.
Schematic of the Audio mute circuit.
We have made a audio mute kit which can be purchased from our website with link below.