12
AUDIO LEVELS ALIGNMENT
This section describes how to determine and set the audio levels.
Audio Levels Overview:
To ensure the best audio quality, the SVR must be configured to match the audio levels used by the radio. The
SVR uses programmable gain amplifiers to accomplish this. Determining the gain settings for these amplifiers is
an involved process, so Midian simplified this process by developing an algorithm that requires the technician to
make only four voltage measurements. From these four measurements, all of the many internal settings are
determined.
Still, getting the best audio quality will likely require a bit of trial and error. The SVR only has control of audio
voltage levels, not input and output impedances. These impedances can dramatically influence the levels.
The Four Voltage Measurements:
An oscilloscope and a communications test set/service monitor are required for the measurements. It is
recommended that the measurements be recorded in units of mV peak-to-peak. Each measurement must be
taken with system modulation at either 60% or 100%, but Midian recommends using 60%
A method for controlling transmit modulation is required for accurate measurements in the TX mode. A small
speaker held in place near the microphone by a rubber band can serve this purpose in most cases. Use a sine-
wave generator to inject a 1000 Hz tone into the speaker. Adjust the output of the sine wave generator so that the
transmitter produces 60% of rated modulation while PTT is pressed. Note that if the audio source (such as a
speaker) is moved even slightly, the TX modulation may change significantly. Care must be taken to avoid
changing the TX modulation while taking the measurements.
The first two measurements must be taken using a radio that has not been modified. The 2
nd
two measurements
require that the SVR is installed and power is applied to the radio/SVR. These measurements must be taken
within 15 seconds of powering the SVR on. This is because the SVR may enter power saving mode after that
time. Measurements made while the SVR is in power saving mode will not be valid. The unit ships with the power
save feature enabled by default. The power save feature can be disabled via the KL-3 programming software so
that it will not interfere with taking measurements, if desired. Please note that the levels provided to the option
board are different between narrow band and wide band.
1.
TX Input:
The goal of this procedure is to determine the audio level that the unit will see at the TX audio
pickup point after it is installed. The unit must be installed and powered-on while making this measurement.
Use the TX Alignment Set-Up procedure and measure the audio level at TP1 on the unit.
2.
RX Input:
The goal of this procedure is to determine the audio level that the unit will see at the RX audio
pickup point after it is installed. The unit must be installed and powered-on while making this measurement.
Use the TX Alignment Set-Up procedure and measure the audio level at TP2 on the unit.
3. In the programming software under audio levels set the TX In to the same level as measured in step 1 and for
a preliminary adjustment set the TX Out for the same level. Set the RX In to the same level as measured in
step 2 and for a preliminary adjustment set the RX Out for the same level. Program the unit.
4.
RX Output:
The goal of this procedure is to determine the audio level that would normally appear at the RX
audio insertion point in an unmodified radio. Using the same RX Alignment Set-Up procedure verify the audio
level at the speaker is still at the same level measured initially in the RX Alignment Set-Up procedure. If not
adjust the RX Out level accordingly.
5.
TX Output:
The goal of this procedure is to determine the audio level that would normally appear at the TX
audio insertion point in an unmodified radio. Using the same TX Alignment Set-Up procedure verify the
modulation is still at 60%, if not adjust the TX Out level accordingly.
