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A sequencer is the key to protecting those expensive microwave or other antenna relays from hot-switching (which destroys the contacts). There is an additional description of a sequencer in the 300w 23cm amplifier article listed on the left.
This sequencer is even better, and will handle up to 4 events; one output is able to sink up to 100v at several amps, and the remaining 3 up to 40v at about 500 ma each.
Typically, one would have the high-capacity port switching the antenna relays, and the others handling amplifier, transverter, or radio switching. The outputs are protected from transient spikes, and the delay is adjustable from a few milliseconds to about one second. LED indicators allow a visual indication of timing on initial set-up.
One additional capability is useful to anyone using a radio that has a transmit inhibit feature (like the FT-897 or FT-817). These radios will hold off RF while an accessory pin is held high. Any of the outputs on this sequencer will do that...the LED feed resistors supply a 12v pull-up potential until pulled low by the sequencer. This not only turns on the LED, it also supplies the required signal for the inhibit feature of the radio. If you have a radio without an inhibit feature, check the work of WA7TZY; he was able to adapt it to his FT736R, which does not have an inhibit feature.