VM1550 Video Modulator

The Drake VM1550 Video Modulator is a high quality, fixed channel, vestigial sideband heterodyne audio/video modulator, designed for adjacent channel operation. The VM1550 is also designed to accept NTSC video and audio baseband signals from a satellite receiver, TV camera, video tape recorder, TV demodulator or similar signal source.

· Low Cost NTSC Modulator.
· 45 dBmV Output.
· IF Loop-Thru for Encoding Systems.
· SAW Filtering.
· Front Panel Control of RF Output Level, A/V Ratio, and Video/Audio Modulation Levels.
· Visual and Aural Over-modulation LED Indicators.
· Complies with FCC Rules Part 76.
· Made in the U.S.A.

The R.L. Drake VM1550 Video Modulator provides a modulated visual and aural RF carrier output on any single VHF Channel 2-13; Lowband Channel A8; Midband Channel A-I and A5-A1; Superband Channel J-W or Hyperband channel AA-HH. All 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. IF loop-thru in the VM1550 provides the capability to replace the standard internally generated IF output, with an alternate source of composite IF, or allows insertion of IF scrambling equipment. All level controls and modulation indicators are located on the front panel for ease of operation.

Specifications

RF
Frequency Range:	54 - 348 MHz
Factory set to one of the following channels:	Cable channels 1-44, 95-99
Output Level:	+45 dBmV. Typically adjustable from +35 to +45dBmV. Note: If an output level of less than +35 dBmV is required, add an attenuator of the appropriate value to the modulator output (e.g. add a 10 dB pad for +30 dBmV output).
Output Impedance:	75 Ohms, return loss of 12 dB
A/V Ratio:	Audio Carrier -20 to -12 dB referenced to video carrier, adjustable
Frequency Stability:	±5 kHz (Visual Carrier)
Intercarrier Frequency:	4.5 MHz
FCC Frquency Offsets:	All aeronautical channels are offset positive, ±5 kHz.
Spurious Outputs:	-65 dBc minimum, measured at -15 dB A/V ratio and with modulator output level of +45 dBmV
Broadband Noise:	-77 dBc, referenced to video carrier. (4 MHz BW and ±12 MHz offset). (-95 dBc @ ±36 MHz of offset)
Video:
Input Level for 87.5%:	1 Vp-p ±3 dB, manual gain adjust with front panel control. Overmodulation LED set for 87.5% depth of modulation indication.
Input Impedance:	75 Ohms, return loss of 18 dB minimum
Frequency Response:	20 Hz to 4.2 MHz, ±1.0 dB
Video S/N:	60 dB minimum, luminance weighted
Differential Gain:	±4% (10 to 90% APL)
Differential Phase:	±4 degrees (10 to 90% APL)
Audio:
Input Level for 25 kHz Peak Deviation:	140 mV minimum. Manual gain adjustment with front panel control. Over-Modulation LED set for 25 kHz peak deviation indication.
Input Impedance:	10K Ohms, unbalanced
Pre-Emphasis:	75 µSec. (Defeatable via internal jumper for BTSC baseband compatibility.)
Frequency Response:	20 Hz to 15 kHz, ±1 dB referenced to 75 Sec. pre-emphasis curve. (20 Hz-100 kHz if pre-emphasis is defeated)
4.5 MHz Intercarrier Stability:	±5 kHz, 0º C to 50º C
Total Harmonic Distortion:	1.0% maximum.
Hum and Noise:	-60 dB minimum, referenced to 25 kHz peak deviation.
Composite IF Loop:
Output Level (V Carrier):	+28 dBmV ±1 dB
Input Level (V Carrier)::	+28 dBmV ±1 dB
Input/Output Impedances:	75 Ohms
General:
AC Power Input:	115 VAC 10%, 60 Hz ,10W
Operating Temperature Range:	0º C to 50º C, ambient
Size:	19" W x 1.75" H x 6.75" D
Weight:	5 lbs. (2.25 Kg)

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