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There are no audio gain adjustments in the Map27 wireless interface module, audio
always passes straight through the WIM.
Required Tools
• A PC or laptop with a serial port and Windows XP
• Zetron M827Base for Windows (version 3.60.146 or later)
• Serial cable (straight-through serial extension cable)
• Small flat bladed screw driver to adjust gain pots on front of MAP27 card
(0.12" max blade width)
• At least one configured MAP27 radio that can be connected
• A digital voltmeter able to read low AC sine wave levels (about 77 mV RMS)
M427 to Console Audio Level Adjustment
This procedure causes the M427 to output a test tone so that the Rx gain at the MAP27
channel card can be adjusted. The Fluke 189 True RMS (Digital) Multimeter or equivalent
device has the accuracy required for the measurements in this procedure. An oscilloscope
can also be used to perform this test, provided it has sufficient accuracy to measure such
small audio signal levels.
1. Connect the COM1 serial port on the PC or laptop to the M427 front panel serial
port using a straight cable.
2. Start the Zetron utility program M827Base.
3. Click FILE, CONNECT, SITE LIST, CONNECT in order to select the
Communications Utility and connect to the M427 being setup.
4. Once connected, click TELCO LEVELS, LINE, AUDIO TO PHONE in order
to select the LEVELS menu and navigate to the dialog that outputs a tone.
5. Set the M427 output slider level to 28.
6. Click the ON radio button to turn on the test tone.
7. At the S4000 MAP27 channel card, connect the AC meter to the front panel RX
and GND test points.
8. At the S4000 MAP27 channel card, adjust the 4-wire RX pot until the meter reads
245 mV (= -10 dBu). 245mV is a RMS level which corresponds to -10 dBu for sine
waves. For sine waves the "peak to peak" level is 2.825 times higher than the RMS
level, so it would be 692 millivolt peak to peak for -10 dBu (= about 700 mVpp).
9. Click OFF at the PC to turn off the test tone.
10. Close the Levels menu.
11. Click FILE, DISCONNECT.
12. Close the M827Base program.
This completes the M427 to console audio level adjustment. The Rx level now set should
be such that a sine wave 60% radio channel deviation causes a -20 dBu level (77 mV
RMS) at the MAP27 Rx test point. This is the same Rx level as the dual channel card
audio level setup (see
Dual Channel Card Audio Levels
MAP27 Wireless Interface Option
on page 181).
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