DRAKE VMD860AS Instruction Manual

VMD860AG VIDEO MODULATOR
®
This instruction manual also is applicable to the
VMD860AS, VMR860AG, and VMR860AS.
The AS models include a built-in BTSC stereo
audio encoder to provide stereo audio.
The VMR models are electrically identical to the
VMD units except that they are designed for
19" rack mounting.
In this manual, only the VMD860AG model is
discussed except where there are differ-
ences. Any differences will be explained.
The R.L. Drake VMD860AG family of Audio-
Video Modulators includes high quality, vestigial
sideband units with synthesized visual and
aural carriers. The frequency agile units allow
front panel pushwheel switch selection of
standard CATV channels 2 through 135, CATV
subband channels, T7 through T14, or VHF/
UHF TV channels 2 through 69. Additionally,
IRC or HRC CATV channel plans may be
selected after moving an internal jumper.
Aeronautical channels are offset positive with
a tolerance of ±5 kHz as required by FCC
rules.
The heterodyne conversion system, in
conjunction with the use of a SAW filter,
ensures optimum vestigial selectivity for
adjacent channel headends.
Broadband noise and in-channel noise are
reduced to a very low levels to provide
excellent performance in multichannel CATV
headend environments.
® is a registered trademark of the R.L. Drake Company
© Copyright 2007 R.L. Drake LLC
The modulators are designed to accept any
standard audio/video source such as NTSC
video and audio baseband signals from a
satellite receiver, TV camera, videotape
recorder, TV demodulator, or similar signal
source. The VMD860AS and VMR860AS can
accept stereo audio inputs and produce a
BTSC stereo audio signal.
When stereo audio is required, the preferred
method of providing a BTSC stereo signal is to
use the VMD860AS or VMR860AS model. No
special setup or test equipment is required.
Also, field-defeatable audio pre-emphasis in
the AG models allows transmission of BTSC
encoded baseband stereo audio signals from
an external BTSC stereo encoder, such as the
Drake MMTS20. Optimum performance requires
proper test equipment for setup with external
BTSC encoders.
The AG models will accept either mono or
stereo inputs and output a mono audio signal
with left and right inputs being summed in the
modulator.
The modulators are designed to accept
standard (negative sync) polarity video at 0.6
to 1.5 Vp-p level. All level controls are located
on the front panel for ease of operation. Audio
and video overmodulation indicators are
provided. Output level is +45 dBmV and is
adjustable downward.
FCC predistortion is provided in the video IF.
P/N: 3852411E-04-2007 Printed in the U.S.A.
1 2 FRONT PANEL CONTROLS and INDICATORS
F1
F1 - POWER/Error Indicator
Lights when the unit is connected to the
required source of DC power via the rear panel
DC INPUT connector. A flashing condition
indicates an invalid channel setting or other
conditions that would cause the unit to operate
on an invalid channel. The RF output is
switched off for flashing (ERROR) conditions.
F2 - VIDEO Level Control
The setting of this screwdriver adjustment
determines the video modulation level.
Clockwise rotation increases the
modulation depth.
F3 - Video OVER MODULATION LED
With a video input applied, adjust (F2) until this
indicator just illuminates, then set just below
this point.
F4 - AUDIO Level Control
The setting of this screwdriver adjustment
determines the aural carrier deviation. Clock-
wise rotation increases the carrier deviation.
F5 - Audio OVER MODULATION LED
With audio applied, adjust (F4) until this
indicator just illuminates on peaks.
F6 - A/V RATIO Control
This screwdriver adjustment varies the level of
the aural carrier over a range from 12 to
20 dB below the visual carrier. The aural
carrier should be adjusted to approximately 15
dB below the visual carrier (normal operation).
Clockwise rotation increases the aural
carrier level.
F2 F3 F4 F5 F6 F7 F8
Figure 1
F7 -T CHANNEL Switch
Set this switch to the "T" channel setting to
enable "T" channel coverage. Use the Channel
Number switch (F9) to select 7 - 14. For normal
CATV or broadcast TV channels, this switch
must be set to the right to enable selection by
the mode switch (F8).
F8 - Mode Switch
Sets the type of channel, CATV or Broadcast
TV ("BCTV"). This switch does not function if
switch (F7) is in the "T" channel position. The
last position of the switch ("+100") sets a
leading "1" for CATV channels 100 through 125.
See Item (F9) for setting the channel number.
Example 1:
Setting for CATV
channel "125"-
Example 2:
Setting for CATV
channel "25"-
F9 - CHANNEL Number Switch
Sets the desired operating channel for standard
CATV channels 02 through 135, "T" channels
T7 through T14, or Broadcast TV channels 02
through 69. See Item (F8) which sets the type
of channel (CATV or Broadcast TV) and sets
the leading "1" for CATV channels 100 through
125.
F10 - RF OUTPUT LEVEL
This screwdriver adjustment permits decreasing
the RF output level a minimum of 10 dB as the
control is rotated counterclockwise. Set the
control for a desired output level.
F9 F10
CATV +100
CATV
BCTV
2 5
T CHANNELS CHANNEL
CATV +100
CATV
BCTV
2 5
T CHANNELS CHANNEL