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TVM-250 drawing


The Belar TVM-250 SAP/PRO monitor is a dual modulation monitor system for television stations broadcasting the MTS Second Audio Program (SAP) and/or PROfessional channels. Operated in conjunction with the Belar TVM-100, TVM-101, or other wideband aural demodulator, the Belar TVM-250 combines simultaneous demodulation and peak modulation measurement of both SAP and PRO subcarriers. An internal RMS metering system indicates injection of both subcarriers and provides direct RMS readings of audio crosstalk and signal-to-noise ratios.

Accurate decoding of the encoded SAP signal is assured by an on-board professional dbx expander card. A crystal-controlled calibration system provides precise references for SAP and PRO carrier deviations, injection levels, and dbx expander performance. SAP and PRO rear-panel audio outputs are active-balanced and drive 600-ohm lines at +10 dBm.

The Belar TVM-250 SAP/PRO Monitor combines all its functions in a single chassis only one rack unit high. Two large LED displays simultaneously indicate peak modulation percentage of the SAP and PRO channels. Four LED's indicate modulation peaks and presence of the SAP and PRO channels, with user-adjustable thresholds. All operational and metering functions can be controlled via the front-panel menu system. One set of UP/DOWN keys provides menu control, another set of keys adjusts operating parameters. Adjustable parameters include peak flasher settings and muting thresholds for SAP and PRO. To facilitate broadcast performance measurements, the menus offer the capability to bypass the subcarrier bandpass filters, to change the SAP detector bandwidth, and to substitute 75 micro-second de-emphasis for dbx companding.

The Belar TVM-250 SAP/PRO Monitor provides an RS-232 output, permitting full operation and readout under computer control. With the addition of a 2400-bps modem and the supplied Wizard software, computer control may be from any off-site location via a standard telephone line. The TVM-250 may also be used in conjunction with other Belar monitors via the Wizard interface. The Wizard system turns an ordinary PC into a powerful tool for display and logging of SAP and PRO modulation parameters


The Wizard Software can operate the TVM-250 remotely and is also used to display real-time graphs. A direct connection or a pair of modems and a phone line may be used. The software is fully password protected with three levels of access. (Software available 1Q97)




Input                                    wide-band demodulated aural composite

Input Level	                         400 mV to 4Vrms for 73 kHz peak deviation

Audio Outputs

  Balanced Outputs	                 +10 dBm, 600   active-balanced, XLR-type connectors

Test Outputs	                         5 Vrms, unbalanced, BNC connectors (75 ohm source)

  Audio Test (auto-ranged)	         1.2Vrms, unbalanced, BNC connector (75 ohm source)

Serial Interface                         RS-232

Unit Interface                           Wizard Standard Interface

Remote Meter Outputs:

  SAP Analog Modulation Meter

  PRO Analog Modulation Meter

  Open collector and relay closures for SAP and PRO peak modulation and carrier presence ndicators

  Data Out - direct coupled PRO demodulator output.  0.9Vrms at 3kHz peak deviation.

SAP Specifications (20 Hz - 10 kHz):

Subcarrier Peak Modulation                 5%

Injection (15 kHz)	                   0.2 kHz

Frequency response:

Bandpass Filter In                        

   Flat	                                   0.4 dB

   De-emphasized                           0.5 dB	

   BTSC	                                   1.5 dB

Bandpass Filter Out

   Flat	                                   0.1 dB

   De-emphasized	                   0.25 dB

   BTSC	                                   1.0 dB

Distortion (THD+N), 10 kHz bandwidth

   BPF In, de-emphasized	          1.2%

   BPF Out, de-emphasized	          0.3%

                   (residual distortion   0.1%)


Signal-to-Noise, de-emphasized	          65 dB

PRO Specifications (30 Hz - 3.5 kHz):

Subcarrier Peak Modulation	           5%

Injection (3 kHz)	                   0.2 kHz

Frequency response:

  BPF In, de-emphasized	                   0.5 dB

  BPF Out, de-emphasized	           0.25 dB

Distortion (THD+N), 10 kHz bandwidth

  BPF In, de-emphasized	                  1.5%

  BPF Out, de-emphasized	          0.3%

                   (residual distortion   0.2%)

Signal-to-Noise, de-emphasized	          65 dB

Dimensions	                          1.75"H x 16.5"D x 19"W

                                  	 (1 EIA Rack Unit)

Power requirements	                 20 Watts, 100-240VAC, 50-60 Hz

Shipping Weight	                         13 lbs

© Copyright 2000 Belar Electronics Laboratory, Inc. All rights reserved. Specifications subject to change without prior notice.

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