RFC-1 Installation page 3.14
3.7.2 Telephone Line Protection
Be sure your local telephone company has installed gas surge arrestors on your incoming telephone lines. Old
installations may contain carbon protectors that tend to provide less reliable protection. Be sure the ground
connection used by the telephone company is an integral part of your station ground system. Sometimes the
telephone company will use a nearby cold water pipe, metal conduit, or isolated ground rod for their ground and this
may be, electrically speaking, quite a distance from your station ground system. Do not disconnect their ground
connection. Instead, add a supplemental conductor from their ground point to the station ground.
We highly recommend that you purchase and install your own telephone line surge protector in addition to the one
installed by the telephone company. Place this between the incoming telephone line and the RFC-1. These spike
protectors are designed to pick up a ground connection through the ground prong on a standard AC outlet so be sure
this is in fact connected to your station ground by the shortest possible means. For best result, install a "dummy" AC
outlet with no AC connections but with a short jumper from the ground terminal on the outlet the metal rack in which
the RP-8 relay panel is mounted. Most protectors have internal, non-replaceable fuses which will blow during a
heavy surge. If this happens, replace the protector. Do not attempt to repair it.
3.7.3 SP-8 Surge Protector
For installations where the maximum in reliability is required we recommend the Sine Systems SP-8 Surge Protector.
The SP-8 provides significant protection against voltage surges from the telephone line, the local telephone and eight
telemetry channels using a combination of ground plane construction, gas surge suppressors, metal oxide varistors,
and carbon film resistors. It mounts directly to the RP-8 Relay Panel.
Damage to the RFC-1 and RP-8 by lightning is not covered under warranty. See the complete warranty for
more information.
3.8 RF Interference
There have been few reported RF problems with the RFC-1 associated with FM transmitters. The RFC-1 has been
tested and found to operate normally in AM RF fields of 632 volts/meter (the ANSI limit for human exposure) with no
additional external filtering. However, extreme conditions exist that require additional external filtering to obtain
reliable operation. Extreme conditions are rare but these problems can be overcome by a combination of one or
more of the following remedies:
• Install an RF filter before the "Line" jack near the RFC-1
• Install an RF filter before the "Phone" jack near the RFC-1
• Loop the ribbon cable several times through a ferrite core at each end
Telephone line RF filters can be obtained through a wholesale distributor or telephone products. Be sure to get an
RF filter and not simply a spike protector.
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