4
Table of Contents / Description / Specifications
2
Caution Statements
2
Important Safety Instructions
4
Table of Contents / Description / Specifications
5
Front/Rear Panel Controls and Indicators
TABLE OF CONTENTS
The R.L Drake VM2050 and VM2550 Video Modulators are high quality, vestigial
sideband units with synthesized visual and aural carriers. They are designed to accept
NTSC video and audio baseband signals from a satellite receiver or similar equipment.
Front panel video and audio level controls with accompanying modulation
indicators permit easy setup of the proper modulation levels. The A/V ratio and
RF output level controls are also provided on the front panel. A rear panel EAS
alternate IF input is also provided.
Synthesized operation provides complete frequency agility, allowing front panel
selection of any standard CATV channel from 2 to 78 (VM2551) and T7 to 78
(VM2050) . FCC required offsets for aeronautical channels are automatically
provided for each channel that requires an offset. For special applications, IRC or
HRC CATV frequencies or off-air broadcast frequencies can be selected from the
front panel.
A high quality IF SAW filter with FCC predistortion eliminates adjacent channel
interference and provides optimum delay characteristics.
A manual or auto-switching alternate IF input, labeled EAS input, is provided for
connection of an Emergency Alert System 44 MHz IF signal. When the EAS IF signal
appears at the EAS input, the main video and audio modulated IF is replaced by
the EAS input signal.
The EAS/Alternate IF feature allows a choice between manual and automatic
selection of the EAS/ALT IF input signal. This is done through a 3 position terminal
strip on the rear of the unit. In the manual mode the EAS/ALT IF feature is
activated by a contact closure switch, which completes a ground connection. In
the automatic mode, two positions on the terminal strip are jumpered together
enabling an automatic detection circuit in the unit. When an EAS/ALT IF signal is
routed to the EAS/ALT port the unit automatically switches to that alternate signal.
DESCRIPTION
SPECIFICATIONS - VM2050 / VM2551
6
Operation
7
Adjustments
8
Channel Assignments
VIDEO INPUT
Connector:
Impedance:
Return Loss:
Video Input Level:
Signal-to-Noise Ratio:
Differential Gain:
Differental Phase:
Over-modulation Indicator:
L/C Delay:
“F” Female
75 Ω
18 dB
0.7 volt Peak-to-Peak
58 dB
2.0%
1.0 degree
87 to 92%
Per FCC Requirements
RF OUTPUT
Connector:
Impedance:
Return Loss:
Channel Modes:
Power Level Range:
Video Flatness:
Carrier-to-Noise:
Broadband Noise:
Spurious Outputs:
Aural/Visual Carrier Ratio:
“F” Female
75 Ω
12 dB
CATV (STD,IRC,HRC) UHF, VHF
(SUB VM2050 only)
+50 to +60 dBmV (in 0.2 dB increments)
fv-0.5 to fv+4.2 MHz : 1.5 dB p/v
-63 dB
-77 dBc
-63 dBc
-15 ± 5 dB
GENERAL
AC Power:
Fuse:
Temperature Range:
Dimensions (WxDxH):
Weight:
117 VAC ± 10%, 60 Hz, 23W max
0.4A Type T 250 V
32 to 122 °F (0 to 50 °C)
19.0 x 14.25 x 1.75 in
(482.6 x 361.95 x 44.45 mm)
7 lbs. (3.18 kg)
MONO AUDIO
Connector:
Input Impedance:
Input Level:
Frequency Range:
Frequency Response:
Total Harmonic Distortion:
Signal-to-Noise Ratio:
Over-modulation Threshold:
RCA
Greater than 10k Ω, unbalanced
0.5 to 4.0 volt Peak-to-Peak
50 Hz to 15 kHz
± 0.5 dB
1% @ 25 kHz deviation
59 dB
25 ± 2 kHz peak deviation
IF
Input/Output Connector:
Aural Frequency:
Visual Frequency:
“F” Female
41.25 MHz
45.75 MHz
Composite IF Output
Aural:
Visual:
+20 dBmV
+35 dBmV
Input/Output Impedance:
Input/Output Return Loss:
75 Ω
16/15 dB
EAS/Alternative IF
Connector:
Input Level:
“F” Female
+30 dBmV @ 45.75 MHz
Switch Isolation: Greater than 60dB
VM SERIES VIDEO MODULATOR
