Technalogix TAV-1000, Manual

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IV-4
Power Divider/Combiner (internal to each TAV-500 enclosure)
A Wilkinson power divider and combiner (identical printed circuit boards) are used to split the RF signal into, and
combine the amplified RF signal out of the (2) P400-VHF final amplifier pallets. Flanged power resistors help
ensure that any differences between the inputs or outputs is balanced.
The Wilkinson design takes advantage of the fact that an impedance transformation can take place across a
quarter-wavelength transmission line if the line has a different impedance than the source or load impedances
being matched. In this case, quarter-wavelengths of 75-ohm coaxial are used to maintain 50-ohm impedances at
the input and output of the Wilkinson divider/combiner. Due to its electrical and mechanical symmetry, the
Wilkinson design’s performance over moderate bandwidths is superior to other types. This design maintains
phase and amplitude equality, in addition to providing isolation and matched outputs.
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. Even though the flanged power resistor is rated for only 250-watts, and there could potentially be 500-
watts being reflected back into the circulator, the software will recognize quickly that reflected power is present
and turn the carrier off. This way, there is instantaneous protection due to the isolator setup and long term
protection due to the software.
Final Combiner (internal to combiner enclosure)
The RF outputs from the (2) TAV-500 amplifier modules then pass into a final enclosure where the signals are
combined, then filtered and monitored once again. The combiner is a 2-way, 1000-watt isolated power combiner
with a maximum phase imbalance of +/-1 degree. Minimum isolation is -18 dB and maximum insertion loss is -
0.45 dB from 170 to 280 MHz. Minimum return loss from ports 1 to 2 (input to input) is -25 dB and -20 dB on
port 3 (output).