S-COM 7K - Command Sources; Local Control; Performing the Tests

7K • Appendix C
C-20
digit can be severely clipped while the low frequency tone is not. The result is
twist, and the solution is to keep the DTMF pad audio at a reasonably low level.
Twist can also be introduced by the repeater receiver if it has poor audio
response, or if a poor impedance match exists between the receiver and the
controller.
Command Sources
The DTMF decoder can monitor all receiver inputs and the phone line for
incoming digits. However, it can monitor only one device at a time. Therefore, a
priority scheme is used to determine which source feeds the decoder at any
given time. If no source is active, the decoder’s input is grounded.
Local Control
You can program the controller with a local DTMF keyboard, if desired.
• Connect the audio from the keyboard to the Receiver #1 Audio Input.
• Connect a switch between the RX #1 COR Input and ground.
• Whenever the switch is ON (closed), the controller will accept commands
from the keyboard.
• Alternately, you can use the same scheme with Receiver #3 and leave the
keyboard permanently connected.
Note: Return the switch to the OFF (open) position when finished
programming, so the repeater Receiver #1 can drive the DTMF decoder once
again.
Performing the Tests
Generate an RF signal on the repeater’s input frequency.
• While listening to the repeater output on an extra receiver, send some
DTMF digits to the repeater.
• You should hear a short burst of DTMF, followed by silence, as the
controller detects the digit and then mutes it.
• If the digits are passed through to the transmitter with no muting taking
place, the DTMF decoder is not recognizing the digits.
There are several areas to check:
• Check the audio level at the output of the Receiver #1 Audio Op Amp; it
should be 700 mV RMS (2V p-p) as discussed in the Repeater Transmitter
Audiosection on page C-7.
• Check the operation of the Receiver #1 COR Input. If the COR input isn't
active, the DTMF decoder will not be monitoring the repeater receiver
audio.
• Check the other receiver COR inputs and their associated DIP switches. If a
higher- priority input is active, the DTMF decoder will be monitoring that
input, not the repeater receiver.
• Check to see if a command was entered to disable the DTMF decoder from
the repeater receiver.