ZETRON 748, Technical Manual

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Installation
12 025-9368H
TESTS AND ADJUSTMENTS
• All steps using a computer or terminal for the setup and adjustment assume you to be in the
Diagnostic menu. From the Main Menu type “5” followed by
ENTER . The Diagnostic menu will
be displayed.
• All steps using DTMF from the phone line for setup and adjustment assume you to be in
program mode already.
• Be aware that you cannot be in DTMF programming and CRT or terminal programming at the
same time.
1. PTT: Verify proper PTT operation by pressing the Connect button on the front panel. The
transmitter should key up at this time. If not, check the wiring between the Model 748 and the
transmitter. Press the Connect button again to unkey the transmitter.
2. TRANSMIT AUDIO: The transmitter deviation must be properly adjusted. If set too low, the
transmit audio will be under deviating and sound low. If set too high, you risk over deviation
there by degrading overall system performance. Refer to the alignment procedure described in
the radio's service manual.
Using a computer or terminal:
Select “TX signaling gain and pre-emphasis adjust” by typing “5” followed by
ENTER
. The
transmitter will be keyed, and a 250 Hz tone will be generated out the transmitter. Each time a key is
pressed, the tone will change to the next one on the list (250, 500, 1K, 2K, 3K).
Using a DTMF telephone:
Using a DTMF phone. call the number the interconnect is on and enter the DTMF programming
mode as explained earlier (when the interconnect answers the phone and prompts you, dial “12748”).
Enter the transmitter setup tests by entering the function code “111#”. The transmitter will be keyed,
and a 250 Hz tone will be generated out the transmitter. Each time any DTMF digit is pressed other
than “#” or “*”, the Model 748 will cycle to the next tone in the list (250, 500, 1K, 2K, 3K).
Adjusting TX audio level:
Press a key twice to jump to the 1Khz tone. Adjust R60 (TX AUD) for 60% of maximum channel
deviation (3Khz typical). JP25 can be used to increase or decrease the output if needed. JP25 in
position A increases the output and decreases it in position B. Once you have the level set for a 1Khz
tone, cycle through the tones and verify a flat response. JP24 can be used to set the tones for a flat
response. If the TX audio injection point is “Mic audio” or another pre-emphasized input, JP24
should be placed in position B (de-emphasis). If the TX audio injection point is “Flat TX” or similar
input, JP24 should be placed in position A (flat).
Using a computer or terminal:
Press ENTER to leave the test.
Using a DTMF telephone:
Press “#” to leave the test mode.
3. CTCSS/DCS ENCODE: To set the CTCSS/DCS modulation level