User's Manual Part 2

IV-4
Isolator
The power amplifier pallets are protected in part by the isolator located in the filter enclosure. It is
actually made up of a circulator and 50-ohm dump resistor. The circulators’ specifications include an
insertion loss of less than 0.2dB with an isolation rating better than 20dB. Any reflected power gets
dumped into the flanged power resistor. This way, there is instantaneous protection due to the isolator
setup and long term protection due to the software.
Filter
The passive bandpass filter rejects spurious and harmonic output products and passes the UHF
channel RF output. The cavity resonator uses aperture coupling. Typical insertion loss is 0.3 dB to 0.6
dB depending on channel frequency. Average roll off is –33 dBc at a point 4.5 MHz below the peak
visual carrier frequency and –30 dBc 9.0 MHz above the peak visual carrier frequency. The filter is DC
grounded on both the input and output for additional lightning protection.
Directional Coupler
The Technalogix dual directional couplers provide DC voltages proportional to forward and reflected
RF power monitoring. These analog voltages are converted for processing using analog-to-digital
converters and provide the control system with valuable data for monitoring purposes. The directional
couplers installed in the power amplifier and filter enclosures have peak detection circuits on the
forward RF power side of the coupler and average detection circuits on the reflected RF power side of
the coupler. This is to allow the end user to set power in a manner that is more independent of
modulation and closer to a true tip-of-sync meter. Hence the readings of the displays in the power
amplifier system are peak for forward and average for reflected. Output power should be set following
the operating procedure found elsewhere in this manual. The directional coupler has a typical
insertion loss of 0.5dB and its Type N connectors can handle 1,500 watts peak.