What’s an Inhibit?

When an Amplifier is in transmit mode, it’s important that the amplifier output doesn’t “see” a short or open circuit.  It wants a clear path to the antenna.  When a Waveguide Switch (which is located at the output of the amplifier (S1B on front panel) switches, the rotating mass of the waveguide switch will cause a harmful reflection back to the amplifier.  So it’s important that the amplifier be turned off while the Waveguide switch completes it’s mechanical travel over to the desired position.  This time period is typically measured in milliseconds, but they are very important milliseconds.

           An Inhibit is a dry contact closure that is provided for each amplifier. 

The inhibit output from the UPL-2 is a form C type relay output.  Most amplifiers require a “short” across two pins that allow normal operation, and an “open” for the inhibit function.  Some amplifiers require an “open” for normal operation, and then a “short” for the inhibit.  The form “C” type inhibit output satisfies both of these cases.

The inhibit is generated from the switch positions that come in from the rear chassis through the waveguide switch connector.  The inhibits are active whenever the waveguide switch doesn’t give a position.

The controller can also be configured in a way where an “External Alarm” (low elevation) causes an inhibit.