Ramsey Electronics SCA1 User Manual - page 16
SCA1
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contained on the received signal. If you have a receiver with such an output
jack, you're in luck; simply hook-up the SCA-1 to that jack.
If your radio does not have a multiplex output jack but you are fortunate enough
to have the schematic of your receiver, then look for the point where the stereo
demodulator is connected to the FM detector. That point will be the baseband
demodulated output.
However, for most of us, we'll have to poke around within our receiver to locate
the proper point in which to find the baseband demodulated signal. Probably the
easiest way is to power up your subcarrier decoder with a speaker attached and
search around within the receiver for the point that allows operation (yes, that's
trial and error, but without a circuit diagram for the receiver under question, it's
pretty much the only way!). A few educated guesses will help us to at least look
in the right places. The demodulator is the last point in the receiver chain where
RF/IF frequencies and their attendant IF transformers are found. So, we can be
pretty certain that the IC chip following the last IF transformer is the detector.
Use a length of coax cable with the center conductor stripped back as a
convenient probe to allow touching various points within your receiver. The coax
shield, of course, is attached to the receiver's ground. The other end of this coax
is connected to the SCA1's input jack, J1. (If your radio is plugged into the AC
line, be sure to use caution when poking around! And, be sure your SCA1,
speaker and other wires are not touching you or your workbench - no need to
risk getting a nasty shock!) With the receiver tuned to a local FM station known
to be transmitting an SCA signal, the coax is probed around various circuit
points until a signal is heard. Leave the SCA1 tuned to 67 KHz (about midpoint
on R1) since most SCA signals are at 67 KHz.
We're sorry we can't be more specific on how to connect to an FM receiver, but
there are many different types of radios on the market and we can't explain them
all! Also, please don't call us and ask us to tell you where to connect up in your
"Blitz-Tone Model K743" FM radio. We simply do not have the man-power to
trace out each schematic for each and every one of our most anxious builders!
The speaker output at J3 will provide plenty of volume to a small speaker, but if
you wish to connect to your big Hi-Fi system, use output jack J2. This output is
suited to connect to your line-level input on your audio amplifier or stereo
system. Just remember that it is mono.
*A note concerning commercial use*
Although you may listen to these SCA broadcasts in you own home, any
commercial usage, such as restaurant, bar, store or even at parties is
considered theft of service and the owner of the copyrighted SCA service
is entitled to collect payment. So, be cool, OK?