User's Manual

IV-3
Filter
The passive bandpass filter rejects spurious and harmonic output products and passes the VHF
channel RF output. The cavity resonator uses aperture coupling and is a linear resonator design.
Typical insertion loss is 0.6 dB to 1.0 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 on 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. The coupler requires 8 to 8.5Vdc to power the internal electronics of the coupler and
is supplied from the control printed circuit board at the front of each enclosure.