Receiver Audio; Transmitter Audio - ACC RC-85 Owner's Manual

RC-85 Repeater Controller Owner's Manual

Receiver Audio

Audio from the receiver needs to be supplied to the controller. The receiver
audio is mixed with other audio sources before being sent along to the
transmitter.
The receiver audio input circuitry to the RC-85 controller allows for a variety of
signal levels and impedances. The audio input is capacitively coupled, which
means that a dc level may be present on the signal supplied. The level is
internally adjustable so that a fairly wide range of input levels is acceptable, but
for best results the input audio should be .5 to 2.5 volts peak-to-peak. If the
level available is lower than this, the gain of the input stage can be increased by
adding a resistor to the controller board at R6, which increases the gain of the
non-inverting op amp input buffer to greater than one (gain = 1 + (100K / R6)).
For example, if 300 mV p-p audio is available, installing a 33K resistor at R6
(gain=4) is equivalent to supplying 1.2 volts at the input and is well within the
desired range.
The input impedance for receiver audio is 100K ohms so that audio may be
picked off from anywhere inside the receiver without loading problems. No
impedance matching is necessary. Find a point past the FM detector where the
audio is de-emphasized and squelch gated to route to the controller.

Transmitter Audio

Audio is supplied by the controller to the transmitter. The audio consists of
receiver, speech synthesizer, tone, link, and phone patch audio, switched and
mixed under the control of the computer in the RC-85 controller. The audio from
the board is high level and low impedance so it's easy to find a good place to
inject it into the transmitter. The microphone input may be OK, but it may be
necessary to knock down the level with a resistor voltage divider. The level out
of the controller is fixed. If the transmitter audio input is very sensitive, it may
be best to reduce the gain of its audio input stage by changing a resistor value.
The audio output is dc coupled - it may be necessary to capacitively couple to the
transmitter depending on where the audio is injected. Remember to use a large
enough capacitor to let the lows through - about 10 uF for input impedances as
low as 600 ohms, and if it's an electrolytic capacitor, install it so that it's
polarized correctly (controller output is at dc ground).
(Installing in Your Repeater) 2 - 3 V3 4/87