Protecting Each I/O

Now let’s examine each of the I/O lines identified in the box-level schematic.  I will divide them into broad categories so that we can discuss them.  Each I/O line represents a potential source or sink (ground) for lightning strike energy, either directly from Mother Nature or indirectly via a connecting wire.  What we need to do is provide a protector that is physically and electrically appropriate for the type of I/O line we are protecting.  The protector has a relatively simple job to do – short circuit when threatened (over voltage).  While this may seem like a relatively simple thing to do, it is sometimes surprisingly complex to accomplish without first sharing much of the strike energy with your equipment.  This is especially important for receivers with sensitive FET front-end stages and electronic to electronic interfaces (RS-232, 422, etc.) where the maximum tolerable interface voltage is just a few volts above the nominal interface operating voltage. 

The best I/O line protectors are connected in series between the surge and the circuit they are intended to protect.  An in-series protector, by design, has the capability to limit the amount of lightning strike energy your equipment will receive.  The “better manufacturers” will specify the maximum amount of let-through energy your equipment will experience during a strike event.  It normally is specified as a quantum of energy in the milli- or micro- Joule range.  When choosing a protector, select the one with the least let-through energy that meets all of the circuit requirements.

Coax

The first category of protector we will examine is the coax line protector.  Coaxial protectors are unique in that they should not add to system SWR or signal loss, and at the same time they need to operate over a very board frequency range while handling both the receive and transmit power levels.

Each coax line leaving the circle around the protected equipment must have an appropriate coaxial protector.  As we will discuss later, the coax protector along with all of the other I/O protectors must be mounted on a common plate (or panel) and connected to an external ground system. 

A typical PolyPhaser protector, for amateur radio use below 1GHz, is either the IS-50UX-series, for flange mounting on a flat surface (upper) or the IS-B50UX-series, for bulkhead mounting through an entrance panel (lower).  While both of these protectors have UHF-female connectors on both the antenna and equipment sides of the protector, by changing the letter ‘U’ to ‘N’ in the part number changes the protector to N-female connectors on both sides.  Connector gender variations are available by adding the suffix –MA for male on the antenna side of the protector, and –ME for male on the equipment side of the protector, to the model number.

Special coaxial protectors to protect the I/O lines for GPS, direct broadcast satellite, over the air TV, and CATV are available, as well as those for tower-top amplifiers and remote antenna switches that require an ac or dc voltage on the center pin of the coax.  All protectors come with the appropriate type of connector commonly used for these applications.