Level setting, Transmitter audio level, Carrier detect adjustments – GAI-Tronics MRTI 2000 (No. PL1877A) Microprocessor Radio Telephone Interconnect Installation & Service Manual User Manual

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PL1877A Microprocessor Radio Telephone Interconnect

Installation

12/10

Level Setting

A service monitor or communications system analyzer is required for level setting adjustments. Connect
the radio’s antenna connector to the communications analyzer and a 50-ohm load. Set the equipment to
monitor deviation at the radio’s transmit frequency.

It is necessary to enter the diagnostic test mode for some of the level setting. To enter diagnostic mode,
press both the

and

DOWN

buttons simultaneously. To step to another test once the diagnostic mode

has been entered, press the

PATCH

ON/OFF

button. To exit, press both the

and

PATCH

ON/OFF

buttons simultaneously. (For more information on diagnostic test mode refer to the Internal Diagnostic
section in this manual.)

Transmitter Audio Level

The following procedure is for setting and measuring transmitter modulator/IDC circuit performance and
overall quality of the landline to mobile audio.

Before proceeding, disable the Private Line encoder output of the transmitter, if used. This may involve
removing the PL code plug in older model radios. For newer model radios, select a carrier squelch mode,
if available, or temporarily program the station to generate carrier only without PL/DPL. If the PL
STRIP function has been properly wired to the station, it is not necessary to perform the above mentioned
procedure. Simply verify that the transmitter is not sending PL/DPL while testing.

Enter diagnostic Test 1 by pressing both the

and

DOWN

buttons simultaneously. This procedure also

activates PTT, and generates a 1000 Hz tone to the transmitter.

If the PL STRIP function has been wired to the station, the transmitter should key and cause the station to
transmit without generating Private Line codes. Adjustment of the transmit level should be made by
pressing the

DOWN

buttons as needed to produce 60% system deviation. Adjust the level to

produce 3 kHz deviation, as indicated by the deviation monitor, for standard 5 kHz deviation radios. For
split channel, narrow-band radios, set the level to produce 1.5 kHz deviation.

After the desired deviation level has been achieved, press the

PATCH

ON/OFF

button. The value set

remains stored in memory unless it is again changed through an adjustment in Test 1. Exit the test by
pressing the

and

PATCH

ON/OFF

buttons simultaneously.

Carrier Detect Adjustments

Logic Carrier Detect

If using the logic carrier detect input, (most recent radios models use this mode) the parameters must be
set as follows:

1 = 1 (RX audio is post de-emphasis, or speaker (muted) source.)

2 = 1 or 0 (Set to match the available level from receiver, refer to Receiver Input Audio Level.

3 = 1 (External logic level carrier detect.)

4 = 1 or 0 (Must be set to match the logic polarity available from the radio. Consult the radio manual or
programming software to determine the polarity of the logic carrier detect output.)

Other parameters must be set as the system requires. Verify the proper selection of RX audio source
from the radio. Some radios, such as the GM300 and MaxTrac Series radios require the positioning of an
internal jumper to select muted, post de-emphasized audio. (JU551 in the “B” position in these models.)
Refer to the radio’s technical manual for information on internal jumpers.

Enter diagnostic Test 3 by pressing both the

and

DOWN

buttons simultaneously. Press the

PATCH

ON/OFF

button until Test 3 is reached.