Cavity Combiner - Theory Of Operation; Replacing The Cavity Combiner - Motorola DIMETRA MTS 4 Installation, Configuration, And Service Manual

Applicant: Motorola Solutions
254 | Radio Frequency Distribution System

Cavity Combiner - Theory of Operation

A minimum of 2 watts is needed at a cavity input. The ATCC will automatically tune in 40 seconds maximum. For
more detail, see the ATCC specification.
Once an RF signal greater than 2 watts is detected, the ATCC tunes the cavity and continuously keeps it tuned over
humidity, temperature and changing transmit frequency, so long as it does not sense one of the following alarm
conditions:
• Channel Spacing alarm
• VSWR alarm
• Failure to Tune alarm
Being tuned means that a cavity is within the insertion loss specification at the frequency of the applied PI/4DQPSK
or QAM4,16,64 signal that is within the average input power range specified above. Being tuned also means that the
cavity peak response is no greater than 25 kHz away from the TX carrier center frequency. If the TX carrier does not
change channel or average power level, the auto tune algorithm will not initiate a re-tuning on its own which exceeds
+/- 300 kHz from the carrier frequency. The only exception occurs when the fine tune timer event happens. The fine
tune timer is used to compensate for large variations in humidity and is default set to 480 Minutes. The Cavity
Combiner is temperature compensated but large variations in humidity can de-tune the cavities up to 150 kHz with
the result of an increasing insertion loss.
When the fine tune timer event occurs, all cavities with RF applied will be re-tuned for maximum output power of
each TX carrier. The fine tune timer can be adjusted to compensate for fast humidity variations; for instance if the
MTS 4 is installed in outdoor sites without air-conditioning. The recommended setting of the fine tune timer, if the
MTS 4 is installed in a controlled environment, is 480 Minutes. For sites where the MTS 4 is exposed to more than
+/- 20% variation in RH, the recommended setting of the fine tune timer is 60-200 minutes depending on the speed of
the variation.
Having a second cavity tune up and pass through the desired channel, the desired channels insertion loss dips no more
than 3 dB more than the max insertion spec for a period of 0.25 seconds. The cavity tuning rate should be faster than
1 MHz per second.
The following list contains control and monitoring features available through the CAN Bus:
• Request current tuned position/frequency of a specific cavity.
• Fine tune time feature, to re-tune each cavity with a specified interval.
• Park an individual cavity, but if RF power is still present, cavity will park and then retune again.
• Input power: request current measured input reflected power of a specific cavity.
• VSWR: request input VSWR of an individual cavity.
• Tuning status of each cavity; parked, tuning, tuned, and parking.
• Alarm conditions of each cavity are reported when requested, including : VSWR, subband, channel spacing and
failure to tune.

Replacing the Cavity Combiner

Process:
1 Remove the Cavity Combiner.
See Removing the Cavity Combiner on page
2 Reinstall the Cavity Combiner.
See Reinstalling the Cavity Combiner on page
Removing the Cavity Combiner
Procedure:
1
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Warning: RF energy hazard and potential equipment damage precaution.
Equipment Type: ABZ89FC5827 / 109AB-5827
254.
255.
Exhibit D2