Technalogix TAV-1000, Manual

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IV-5
Directional Coupler (internal to TAV-500 and combiner enclosures)
The Technalogix dual directional couplers provide DC voltages proportional to forward and reflected RF power
monitoring. These analog voltages are converted for processing using a 10-bit analog-to-digital converter 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 by the following procedure:
THE POWER OUTPUT SHOULD NEVER BE ADJUSTED EXCEPT
UNDER THE TEST CONDITIONS OF NO AURAL CARRIER, WITH THE
VISUAL CARRIER MODULATED WITH SYNC AND BLANKING.
The directional coupler has a typical insertion loss of 0.05dB 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.
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.