CVA-3120
VA-700
I.R.T. Communications Pty Ltd | www.irtcommunications.com
Page 19 of 23
Revision 10
CONFIGURATION
The CVA-3120 requires no configuration or adjustment for normal applications other than as detailed in the
installation procedure.
Response time:
If the damped response time is unsuitable for the proposed application the value of C6 may be changed
accordingly, but should not be omitted altogether. The chosen value of 10
µ
F gives a time constant of
approximately 0.1 seconds which is considered a good compromise for normal broadcast use.
Maximum gain:
The 6 dB amplifier U2 may be adjusted to greater or lesser gain settings if required although this should rarely be
necessary. The combined gain and EQ circuits of the VA-700 and the CVA-3120 should be sufficient to compensate
for any losses in normal circuits.
The maximum gain is set by resistors R6 and R7 and the gain is determined by the equation:
V
O
= [(R
7
+ R
6
)/R
6
] * V
IN
Where V
O
is the output voltage; and V
IN
is the video input signal.
Maximum attenuation:
If greater attenuation is required the value of R 2 may be adjusted to provide the necessary gain range. Please note
however that some performance specifications may not be met if the gain range is greatly extended.
External DC control:
The attenuator network on the control input is adjusted for use with a 0 to 12 Vdc control signal and exhibits a
dead band at the maximum gain position (0 Vdc) to ensure that this can be achieved.
If control voltage ranges other than 0 to 12 Vdc are required to be used then the resistor values of R 2 & R 3 may
be adjusted to provide the correct division ratio for the input voltage range so that the voltage at pin 3 of U 1
varies between 0 and 0.5 Vdc for a 6 dB adjustment range.
Care should be taken to ensure that R 2 is kept to a sufficiently high value to offer protection to the IC input and C
6 should be adjusted to provide a suitable damping factor for noise which may be induced into the control line.
For more information on using this input please consult the Gennum data sheet for the GT4123.