11
HARDWARE ALIGNMENT
This section describes how to determine and set the audio levels, the default programming file contains the audio
levels found at the time this manual was written. Default files can be found at:
C:\Apps\Midian\MPS\MPS_v5_xx\Additional Default Files\GPS-2\Icom
Audio Levels Overview:
To ensure the best audio quality, the GPS-2 IC2 must be configured to match the audio levels used by the radio.
The GPS-2 IC2 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 GPS-2 IC2 only has control of
audio voltage levels, not input and output impedances. These impedances can dramatically influence the levels.
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. Set the radio programming software for an option board and set all parameters to accommodate a GPS-2 IC2
board then program the radio.
4. Install the unit 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.
5. While in receive mode, and using the
EXACT
set up as in step 2, measure the signal level at TP-2.
6. In the software under audio levels set the TX IN to the same level as measured in step 4, for a preliminary
adjustment set the TX OUT for the same level. Set the RX IN to the same level as measured in step 5 and for
a preliminary adjustment set RX OUT for the same level. Program the unit.
7. 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.
8. 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.
Programming the Audio Levels:
After determining the audio levels at the audio hookup points, it will be necessary to program the GPS-2 IC2 to
match these levels. In the programming software, there is a slider control on the Audio Levels Screen for each of
the of four audio hookup points. Locate the column that corresponds to the modulation and units of measurement
