Microphone Placement - Radio Communication Labs SAFE SPEAK HF3 User Manual

The PTT transmit line to the radio is an "open collector" output that is driven
logic low (i.e. to ground) during transmit, as required by most transceivers.
In the rare instance you need to invert the sense of this PTT line, you can
solder a jumper on the PCB at position "A" (between IC2 and Q1) which will
invert the logic of the PTT line to the radio.
Rear Interface Connectors
NAME PURPOSE
12V DC External DC power.
Only used when no DC
power is available from the
Mic connector
RADIO Provides interface between
the HF3 and the radio
transceiver
PTT Input socket allows an
external PTT momentary
switch to be utilised
MIC Input socket for the electret
microphone (supplied)

Microphone Placement

Position and install the microphone as close as possible. The car's "A Pillar" is
an ideal location. Connect the 3.5mm plug to the MIC socket on the HF3.
CONNECTOR NOTES
DC Power Connector Voltage range from 5v to 30v DC.
Centre pin is positive. In vehicles, fusing
and additional DC filtering is required.
RJ45, 8P8C modular 1 – DC Power, 5v to 10v typically
socket 2 – Not used
3 – Not used
4 – PTT (Transmit)
5 – Ground
6 – Mic Audio
7 – Ground
8 – Not used
2.5mm mono Tip – Connect to Ground to transmit
tip/sleeve socket Sleeve – Ground
Use a normally open momentary
contact pushbutton switch
3.5mm stereo Tip – Audio
tip/ring/sleeve socket Ring – 3.3v DC to supply power to an
electret mic element via 2K2 resistor
Sleeve – Ground
6