C.E.S. Model SDI-50 Manual, Level Adjustments
LEVEL ADJUSTMENTS
Now that all connections have been made to the Model SDI-50, the next
step is to perform all level adjustments required for proper operation
in your system. An FM service monitor, an oscilloscope, or AC RMS
voltmeter, and the DTMF encoder provided with the SDI-50 are required
for level adjustments.
The numbers in parentheses show the location on the assembly drawing
the pots can be found.
5.1 NOISE CONTROL R91
(5,C) The noise control is used for muting the audio (squeich noise),
when no carrier exists on the radio channel. This condition is
indicated by the MOBILE DETECT LED on the front panel of the Model
SDI-50. When the LED is illuminated, this indicates that the SDI-50
detects carrier. When it´s extinguished, no carrier is detected.
Jumper JMP6 shouLd be in position D/A if carrier alone is used to
detect mobile presence. If a CTCSS or DCS decoder is going to be
used, see the CTCSS section in this manual for other JMP6
configurations.
To adjust the Noise Control, use a small alignment tool to rotate R91.
Start from a fully counter-clockwise position and note that the Mobile
Detect LED on the front panel is "On". Turn R91 clockwise until the
LED turns "Off". Continue rotating the adjustments about 1/8 of a
turn further. Please note that the Noise Control can be turned even
further clockwise to inhibit very weak and noisy signals from
accessing the interconnect. Use your own judgement as to the quality
of transmissions from mobile stations required to use your system. If
you can not adjust R91 so that the LED extinguishes, then re-check the
Receiver Discriminator Audio connection in the Installation Section
and re-check JMP6 for proper placement.
5.2 RECEIVE AUDIO LEVEL R60
(5,D) The RX AUDIO LEVEL controls the signal level from the radio
receiver to the telephone line and DTMF level to DTMF decoder. To
adjust the RX AUDIO LEVEL, set your service monitor to genérate an 800
Hz. audio signal at 4.0 Khz. deviation on the receive frequency of
your system. Connect an oscilloscope or AC RMS voltmeter to pin 7 of
U16. Push the Connect switch on the front panel of the SDI-50, and
carefully adjust the RX AUDIO LEVEL adjustment, R60, for a 3.0 volt
peak to peak reading sine wave (1.0 Vrms). Adjusting R60 beyond this
level will result in a distorted and clipped signal. If
Page # 15
