GAI-Tronics MRTI 2000 (No. PL1877A) Microprocessor Radio Telephone Interconnect Installation & Service Manual - Manual (Page 24)

Installation PL1877A Microprocessor Radio Telephone Interconnect
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While in Diagnostic Test 3, ensure that the Carrier Detect Input LED (marked PWR for this test) goes on
and off at the desired RF threshold levels (generally 10 to 12 dB sinad). The actual squelch sensitivity is
determined by the radio in this case. Any adjustments to squelch sensitivity must be made with the radio.
When complete, exit the Diagnostic Test Mode by pressing the
UP and PATCH ON/OFF buttons
simultaneously.
Internal Noise-Operated Squelch Adjustment
This procedure applies only if using the PL1877A internal noise-operated carrier detect. Its use requires
that receive audio is taken from the discriminator or detector prior to any high-frequency filtering. The
primary use for this method is Signal Search Simplex, where its use is required. Refer also to page 83 of
this manual for the Signal Search Simplex mode. Ensure that these basic parameters are set as follows:
1 = 0 (RX audio source has been pre-emphasized.)
2 = 1 or 0 (Set to match available detector level, refer to Receiver Input Audio Level)
3 = 0 (Internal carrier detect.)
5 = 0 (Internal squelch selected.)
With the PL1877A in the idle state, with no RF signal applied, observe the BUSY LED. Adjust control
VR201 marked SQL with a small screwdriver until the LED extinguishes. (This adjustment is accessible
on the rear of the PL1877A housing.) Then, from the communications service monitor, generate a signal
on the receive frequency, and verify that the LED lights at 10 to 12 dB sinad. Readjust the control as
needed to obtain the desired level of squelch sensitivity. Finally, ensure that the LED extinguishes when
the RF signal is removed.