Preselector Field Tuning Procedures - Motorola MTR2000 T5544 Instruction / Field Service Manual

Troubleshooting
5

PRESELECTOR FIELD TUNING PROCEDURES

Depending on the configuration, the station may have an external preselector assembly, an internal preselector, or
both. The external preselector assembly is a 5-pole bandpass filter equipped with tuning slugs to adjust the pass-
band corresponding to the operating frequency(s) of the station. For the internal preselector, circuitry in the Re-
ceiver Module provides a varactor-tuned bandpass filter which adapts to the required frequency range under the
control of the Station Control Module.
The external preselector must be retuned if the preselector assembly or Receiver Module are replaced in the field,
or if the station operating frequency(s) are modified. The internal varactor-tuned preselector is factory-tuned to
cover the relevant frequency band in its entirety, and is retuned only if the Receiver Module is replaced in the field
or if there is a suspected problem with the Receiver alignment. The tuning procedures follows.
STOP
IMPORTANT
External Preselector Tuning Procedure
STOP
IMPORTANT
34
If the station has both an external preselector assembly and an internal
varactor-tuned preselector which must be retuned, you must bypass the
external preselector and retune the varactor-tuned preselector first, then
reconnect the external preselector and retune it. Also, since this is a non-
standard configuration, you can expect a slight degradation in the re-
ceiver sensitivity (approximately 1.5 dB) due to preselector insertion
losses.
Tuning for best SINAD response DOES NOT result in optimum tuning
of the preselector assembly. You must use this field tuning procedure to
obtain optimum preselector performance.
Required Test Equipment
The following test equipment is required to properly tune the external pre-
selector assembly:
• RF signal generator – Motorola R2600 or R2001 Communications An-
alyzer (see note below), or HP8656A signal generator (or equivalent)
• Dip/Peak Monitor – HP435B Power Meter (or equivalent) with
HP8484A sensitive power head, Boonton Model 92E with BNC input,
or R2001/R2600 using the spectrum analyzer function
• Torque driver capable of delivering 1.36Nm (12 in-lb) of torque and
10 mm deep well socket
• Tuning probe – Motorola Part No. 0180763D22, p/o TRN7799A
• Flat-blade screwdriver
68P81096E17-E
09/30/05