1296 MHz 2-way combiner.
The combiner is build using 25 x 25 mm aluminum profile with a 8 mm copper tubing as center conductor. The hole in the middle is for soldering the center conductor. This hole and the ends must be closed before installing the combiner outdoor.
This design is a combiner made up from two quaterwave transmission lines connected together. The transmission line is therefor one halfwave long - or 116 mm. 50 ohm N-connectors for the two antennas are placed at each end and in the middle another N-connector for the output.
The two quaterwave sections must transform each antennas impedance of 50 ohm into
100 ohm, so when paralleled in the middle a 50 ohm impedance is again established.
The correct transmissionline impedance is the square root 50*100 or 70.7 ohm. With
the suqare tube having 22 x 22 mm inside dimension, the centerconductor must have
a diameter of 7.38 mm. In this design a standard 8 mm cobber tubing was used.
Measured return loss is -20 dB with 3 dB splitter loss.
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