Modulation Sciences SRD-1 Stereo Reference Decoder

The SRD-1 is the industry standard TV stereo decoder for critical measurements. It serves a dual-role as a stereo measurement instrument and an audio-quality monitor.

And the SRD-1 offers full compliance to BTSC standards yet works with test equipment already owned by most stations, saving costs over other BTSC-capable monitors.

A TV station can calibrate the SRD-1 to verify its performance to BTSC Recommended Practices. Its performance has not only been field-tested, but has also been verified by an independent Professional Engineer. A copy of the full report is available from Modulation Sciences at no cost.

The SRD-1 lets users select four operating modes: Equivalent mode: either sum and difference or left and right and BTSC mode: sum and difference or left and right. It also has selectable deemphasis and two independent sets of audio outputs -- precision and balanced line. Two preset inputs allow for rapid selection between two composite stereo sources.

The SRD-1 maintains performance over temperature and has a test set-up to permit field verification of performance. SRD-1 achieves laboratory accuracy at a modest price that is half to a third what other BTSC capable monitors costs. SRD-1 is unique in being the ONLY television stereo decoder delivering laboratory grade performance independently -- without reference to the encoder.

The SRD-1 is simply the most accurate way to assure a TV station's stereo performance and compliance.

• Four operating modes for added versatility

Select any of four operating modes from front panel push buttons in order to examine the transmitted signal in every possible way.

1.1. BTSC Mode: Left and Right outputs.

1.2. BTSC Mode: Sum and Difference outputs

1.3. Equivalent Mode: Left and Right outputs

1.4. Equivalent Mode: Sum and Difference outputs

• Switchable Deemphasis

A precision 75 microsecond deemphasis may be switched in for any mode. This allows the SRD-1 to be used for either measurements or accurate listening.

• Two sets of audio outputs

Because the SRD-1 serves a dual role as a measurement instrument and an audio-quality monitor, two sets of outputs are provided--precision and balanced line. Each set is electrically independent. 

• Two selectable preset inputs

The SRD-1 provides for two preset, switch selected inputs. This allows for rapid selection between two composite stereo sources without the need to reset input levels.

• Field-measured compliance to BTSC

The SRD-1's calibration can be verified against the BTSC tables by station personnel--in the field.

• Easy verification procedure

A simple verification requires only an audio oscillator, a frequency counter, and an accurate AC digital voltmeter. A major recalibration requires an accurate phase meter in addition to those three.

• Level Setup Accurate to ± 0.03 dB

The accuracy of any BTSC stereo decoder is limited by how precisely its input level can be adjusted. An error in the composite input of ± 0.3 dB will limit the maximum measurable separation to 30 dB. A maximum performance of better than 50 dB separation is desirable if the SRD-1 is to accurately measure stereo generator performance greater than 40 dB.

• Use with any TV stereo generator

Because it operates independently of the stereo generator, the SRD can be used to set up and measure any BTSC stereo generator.

• Maintains performance over temperature

Modulation Sciences have designed the SRD-1 stereo reference decoder to maintain specifications over a range of 10 to 45 degrees Celsius. This impressive performance isn't just "spec" talk. We've proven it in our own environmental chamber.

• Fast, easy setup
• Operates with Tektronix Demodulators
• Compliance to BTSC certified independently
• Less than the cost of BTSC-capable modulation monitors
• Simple to test
• Typical MTS test setup using SRD-1
  

Size
Inches (mm) H x W x D
Front Panel: 3.5 x 19 (88.9 x 483)
Chassis: 3.5 x 17 x 14.37 (88.9 x 432 x 365)

Power
95 to 130 VAC, 50/60 Hz, 12 W maximum
190 to 260 VAC option available

Temperature Range
10° to 40°

RF Protection
All inputs and outputs RF suppressed, power supply RF suppressed and shielded from main circuitry.

INPUT/OUTPUT CONNECTIONS

Composite Input
BNC connector, rear panel
"floating" input, 10k W impedance.
Level range at 25 kHz deviation
.085 to .85 VRMS, .24 to 2.4 V P to P.

Calibration Input
BNC connector, rear panel
When CAL position selected, drives M & D inputs.
For use with Gibson calibration tables.1

Audio Outputs
Test outputs
Unbalanced BNC connectors, front and rear panels
Left/Right or Sum/Difference as selected.
<1 W source impedance
minimum load impedance 600W
L or R output at 25 kHz deviation of L + R 7 dBm
Sum output at 25 kHz deviation of L + R 13 dBm
Difference output at 50 kHz deviation of L - R 13 dBm
Balanced line outputs
No. 6 screw terminals, rear panel
Left/Right or Sum/Difference as selected
~100 W source impedance
minimum load impedance 600W
L or R output 25 kHz deviation of L + R 7 dBm
Sum output 25 kHz deviation of L + R 13 dBm
Difference output at 50 kHz deviation of L - R 13 dBm

INDICATORS

Stereo
SRD is receiving a stereo signal.

Mono
SRD is receiving a monaural signal.

Ref level
Green
Input signal is within setup window
Red
Input is above setup window

SEPARATION
(See graphs, page 5)

75 µsecond equivalent mode
Greater than 55 dB 50 Hz to 15 kHz.

BTSC encoded
Greater than 45 dB 50 Hz to 14 kHz.

CONTROLS

Mode Select
Selects among the following output modes:
Equivalent 75 µsecond
Sum & Difference
Left & Right
BTSC
Sum & Difference
Left & Right (normal operation)
Calibrate
Places the M & D inputs in parallel for calibration
to the Gibson tables.

Input
Selects between preset inputs A or B.

A & B Trimmers
Adjusts input composite level to fall within the setup window
for each of the preset inputs.
75 µSecond Deemphasis
Switches the 75 µsecond deemphasis in or out.

FREQUENCY RESPONSE

75 µsecond equivalent mode (L, R, or L + R)
±0.1 dB 50 Hz to 14 kHz
no more than - 1.0 dB at 15 kHz

BTSC encoded (L + R modulation)
Same as above.

BTSC encoded (L or R, 10% M channel modulation)
±0.1 dB 50 Hz to 5 kHz
±0.2 dB 6 kHz to 14 kHz
no more than - 2.0 dB at 15 kHz

TOTAL HARMONIC DISTORTION

75 µsecond equivalent mode
(100% M channel modulation)
0.02% max.

BTSC mode
(70% M channel modulation)
0.15% 50 Hz, 0.07% 100 Hz, 0.04% above 200 Hz.

INPUT SETUP WINDOW WIDTH

0.03 dB

SIGNAL - TO NOISE - RATIO

Equivalent Mode, with 75 µsecond deemphasis
Left channel - 84 dB
Right channel - 84 dB
Main channel greater than 84 dB
All below ± 25 kHz deviation.
L - R subchannel greater than 88 dB
below ± 50 kHz deviation.

BTSC Mode, with 75 µsecond deemphasis
Left channel - 86 dB
Right channel - 86 dB
Main channel greater than 89 dB
All below ± 25 kHz deviation.
L - R subchannel greater than 89 dB
below ± 50 kHz deviation.