Vectronics VEC-422K - Manual (Page 23)

VEC-422K Owner's Manual SCA Decoder Kit
21
music for restaurants or hotels. You may monitor these programs, providing
they are for your own or immediate family’s enjoyment. Using them in a place
of business to provide background music for customers without being a
subscriber is theft of service. Stock reports are carried on some SCA systems.
Again, monitoring the programs for your own enjoyment is legal, using the
information to make investments is a form of personal gain and is illegal. (In
most instances stock services require special decoding equipment.) The
Communications Act of 1934 also strictly prohibits divulging the contents of any
intercepted private radio communications. The laws governing the interception
and monitoring of private radio communications are very dynamic and ever
changing. Protect your rights as a radio hobbyist by using the VEC-422K in a
responsible and legal manner.
IN CASE OF DIFFICULTY
Only high-quality components and proven circuit designs are used in Vectronics
kits. In very rare instances is a defective component the source of a problem.
Replacement of defective parts is covered in the Warranty section. Ninety-five
percent of the kits returned for factory repair are due to soldering problems or
parts in the wrong locations. We advise repeating the assembly instructions
step-by-step, looking for mistakes or soldering problems. Be especially wary of
electrolytic capacitors and semiconductors. Kit builders often miss obvious
mistakes. What is needed is a “fresh” set of eyes. Enlist a friend to go over your
work.
Always check the obvious! Is the battery dead? Is the power switch on?
The majority of reception problems can be traced to a few major causes. The
FM signal must be strong—if the signal is weak the SCA subcarrier will also be
weak, and the XR2211 decoder may not be able to lock to it. The SCA
subcarrier modulation is typically 10% of the total FM deviation. The SCA
subcarrier must be taken directly from the FM detector stage, before any RC de-
emphasis circuits or filters limit bandwidth and reduce the SCA signal. Not all
FM stations broadcast SCA signals. Nor, are the SCA subcarriers always
present when there is no programming activity. The advanced test procedure
shown earlier may be used to prove whether there is a problem in the unit, or
with the receiver hookup.
THEORY OF OPERATION
Recovered audio from the FM detector is sent directly to the SCA Adapter input.
The signal pick-off point must be directly from the detector output before any
de-emphasis takes place.