GAI-Tronics MRTI 2000 (No. PL1877A) Microprocessor Radio Telephone Interconnect Installation & Service Manual - Manual (Page 150)

Pl1877A – Radio Installation PL1877A Microprocessor Radio Telephone Interconnect
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Earth ground - Run the supplied #12 (or larger) wire from the GND terminal on the rear of the PL1877A
to the base station chassis ground. This wire must be as short as practical, not coiled, and fastened
securely to the base station chassis. If this is a control station is a repeater system that transmits PL/DPL
during transmit turn-off delay, it is necessary that the repeater be set for zero turn off delay. (See Note 2).
All other parameters are programmed as applicable to system requirements. Refer to the Parameters
Modification Procedures and then the Level Setting sections of this manual.
Parameter Setting
1 0 (de-emphasis)
2 1, JU202 OUT (low-level source)
3 0 (internal carrier detect)
4 Don’t care
5 0 (internal squelch for carrier detect)
6 0 (No PL detect input required)
1 (PL detect input required)
7 1 (PL detect input is active high)
9 1 (simplex)
10 0 (active low PTT sense input
70 0 (signal search)
1 (enhanced VOX, requires the enhanced VOX option)
N OTES :
1. MAXAR Quadrature Detector Adjustment can cause receiver response time problems, especially in
DPL systems. This can adversely affect PL1877A operation, especially in the Signal Search mode.
The following procedure ensures the shortest possible receiver PL/DPL response time and is the
procedure currently being used on all MAXAR, MOXY and MAXAR 80 radios being shipped from
the factory.
a. Transmit into a 50-ohm load at 13.8 V.
b. Note meter 2 (quadrature output) using a high impedance DVM (may be necessary to measure on
the radio circuit board if the meter 2-wire was used in the PL1877A installation).
c. Dekey the radio.
d. Inject a 10.7 MHz signal into the IF of the MAXAR radio.
e. Adjust the quadrature coil (L18 or L23) for a meter 2 reading as measured in step “b”, ±0.1 V dc.
This procedure reduces or eliminates the pulse to the PL/DPL deck caused by the difference of
quadrature voltage between transmitting and receiving an on-frequency signal. Note that a mobile
transmitting off frequency can cause the same problem.
2. Repeater transmit turn-off delay in repeater control station installations:
When the PL1877A is being installed in a control station controlling a repeater, it is necessary to
ensure that the repeater does not stay on the air after the control station unkeys. If the PL1877A
detects carrier (and PL/DPL, if applicable) after unkeying the control station, it erroneously is seen as
a mobile transmission. In systems that require PL/DPL and retransmit (not generate), no problem is
encountered with the PL/DPL signal (such as most community repeaters) since carrier only is not
seen as a system mobile. Some repeater stations have a jumper for turn-off delay but many delay
turn off more than a second even though the “0” position is selected. In these cases, reducing the
timing capacitor to a much smaller value produces the required results (for example, changing C11
on a MICOR repeater TLN4662A squelch gate module from 68
µF to 4.7 µF).