Control Circuits

Control circuits for all external, especially tower mounted, circuits must be protected.  In the radio station, this usually consists of an antenna rotator.  Since most of the control circuitry managing the antenna rotator is relay based (as opposed to electronic), we can use a less expensive shunt type protection device effectively.  The PolyPhaser IS-RCT is capable of protecting up to eight circuit lines with an operating voltage of up to 82Vdc. 

There are some new rotors in the market that use optical encoders and a modestly protected digital interface.  These must also be protected, however, the method of protection will change since it is an electronic interface and not a mechanical (relay) interface.  Once the peak operating interface voltages are determined, it is relatively straightforward to choose the appropriate inline protector for the individual signal pairs.

Other

Depending on the complement of equipment in the radio room there may be additional I/O lines remaining to be covered.  While I’ll address a few of the more common ones, the others will probably require some special attention based on the physical conditions of the site. 

For those radio rooms that have over the air TV or CATV, its protection is similar to the coaxial protectors described above with the exception that the impedance of the unit is 75 Ohms and uses F-type connectors.  The PolyPhaser IS-75F-C1 protector is a flange-mount coaxial protector similar in size to the coax protectors described above.

For single and dual-LNB DBS satellite dishes the protector is required to have a very broad band-pass and allow DC on the coax center-pin.  The PolyPhaser IS-SB75F is intended for single LNB systems while the IS-DB75F is for dual LNB-systems.  Physically these units are similar in size and mount to the rotor-line protector described above.

The GPS is somewhat special because there is usually a dc voltage present on the coax center-pin.  A high quality protector will separate the RF from the dc and protect each to its own voltage and power specification.  There are several PolyPhaser models that can provide protection for this circuit.

I/O Wrap-up

Other than a few erasure marks or some re-drawn lines, every line that penetrates the circle and goes to the edge of the page should have an identified protector.  If you are having trouble, identify the problem area and mail the drawing to me.

The next step in the process will take us away form the theoretical work that we have been doing and into the real world of practical design and component layout.  It’s not hard, but there are a lot of things to consider as we take each step.  Most of the considerations will be unique to the physical circumstances associated with your radio room.