6
HA DWA E ALIGNMENT
This section describes how to determine and set the audio levels.
Audio Levels Overview:
To ensure the best audio quality the scrambler must be configured to match the audio levels used by the radio.
The scrambler 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 scrambler only has control of audio
voltage levels not input and output impedances. These impedances can dramatically influence the levels.
After the latest MPS has been installed default programming files for specific radio models can be found at:
C:\Apps\Midian\MPS\MPS_vX_xx\Additional Default Files\VS-1xxx\Icom\VS-1xxx
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%
1. A method for controlling transmitter 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
2. Using a service monitor send a fully quieting signal (-50 dBm) to the receiver with a 1000 Hz tone at 60%
modulation adjust the volume of the receiver to a comfortable listening level and measure the audio level at
the speaker using an AC coupled oscilloscope.
3. Measure the TX and RX audio levels at the jumper break points. This will be the preliminary Voice Audio
Level set in the MPS for TX out and RX out.
4. Break the RX TX and PTT jumpers
5. Install the VS-1xxx and power up the radio using the EXACT set up as in step 1 and while in transmit mode
measure the signal level at TP-1*.
6. While in receive mode and using the EXACT set up as in step 2 measure the signal level at TP-2*.
7. In the MPS under audio levels set the TX IN to the same level as measured in step 5 for a preliminary
adjustment set the TX OUT for the level measured in step 3. Set the RX IN to the same level as measured in
step 6 and for a preliminary adjustment set the RX OUT for the level measured in step 3. Program the VS-
1xxx.
8. Using the EXACT set up as in step1 and while in transmit mode verify the modulation is still at 60% if not
adjust the TX OUT level accordingly.
9. While in receive mode and using the EXACT set up as in step 2 verify the audio level at the speaker is the
same level that was measured in step 2 if not adjust the RX OUT level accordingly.
*Please reference the pictorial at the end this manual for location of test points.*
