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The industry standard for MTS test and measurement.
Certified compliance to BTSC standards can be used with any
TV stereo generator. Provides four modes of operation. Maintains
performance with varying temperature.
SRD-1 sets the standard
for precision MTS test and measurement. The SRD-1 stereo
reference decoder is the most accurate monitor on the market.
It works with test equipment your station probably already
owns, so it costs less than other, less precise test equipment.
Modulation Sciences has designed the SRD-1 with painstaking
detail and individually calibrates each production model in
basic units: voltage, frequency and phase. Verifying the original
calibration requires only an audio oscillator, frequency counter
and an accurate AC digital voltmeter.
Station personnel can
calibrate the SRD-1 to verify its performance to BTSC Recommended
Practices (Appendix D). When an SRD-1 is used to calibrate
any television stereo generator, it provides traceability
to the BTSC standards.
Why is this important?
This traceability to
the original system specifications "closes
the loop" of BTSC stereo generation, demodulation and standards.
Contrast this with other approaches, where the user is asked
to accept such compliance on faith--without the means to verify
that compliance.
Only the SRD-1 gives you proof by direct user
measurement. And only the SRD-1 gives you verified performance
by documentation. Modulation Sciences used the services of
an independent professional engineer whose certified report
verifies the SRD-1's performance and details the measurement
procedure. You can put your trust in the SRD-1.
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
The BTSC Left
and Right mode delivers audio as it would be recovered in
a viewer's home. The Equivalent Mode (test mode) demonstrates
the performance of the system with the BTSC companding system
replaced by 75 microsecond deemphasis network as specified
by the BTSC. The BTSC Left/Right mode provides the signal
through a BTSC precision expander.
In the Sum and Difference
modes of equivalent and BTSC, the L+ R baseband and the L-R
subchannel may be examined individually.
This variety of methods
to test the transmitted signal means that you never have
to guess about how the signal is being received or whether
or not it complies with the FCC rules. With the SRD-1, you
always know how your signal performs.
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.
BTSC standards specify separation
measurements be made with preemphasis and deemphasis removed.
However, many operational measurements, such as dynamic separation,
as well as off-air listening require preemphasis/deemphasis
to be on, as in the "real
world".
Switchable deemphasis provides a way to meet all of
these needs.
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.
The BNC connectors on the front and back panel are
for precision measurements. They are driven directly by accurate
operational amplifiers employing resistors in their feedback
network matched to 0.1%. These have an extremely low output
impedance so measurements are accurate regardless of loading.
The
screw terminal outputs on the rear are balanced, line level
outputs. They provide a nominal level of 0 dBm and are coupled
to the circuit using high quality transformers intended to
drive a standard audio monitoring system.
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.
Because setting
the input level to a BTSC decoder requires using the Bessel
null procedure, it cannot be done during the normal program
day. Therefore, to be able to select between two sources
of composite stereo, the input level for each must be preset.
An example of this might be choosing between the output of
a demodulator, and monitoring directly the output of the
stereo generator.
This arrangement allows the engineer to determine--during
normal programming--if a problem on the air is being introduced
by the transmitter exciter itself or is coming from the stereo
generator.
Field-measured compliance to BTSC
The SRD-1's calibration can be verified against the
BTSC tables by station personnel--in the field.
The BTSC standard
for television stereo is not embodied in a circuit card, no
matter who the manufacturer is. Instead, the standard is a
set of equations that can be found in the FCC report OET-60.
The equations themselves would be awkward to use, so an engineer
(Jim Gibson of RCA Labs) used the equations to produce an extensive
set of tables that describe the input-output performance of
an ideal BTSC encoder/decoder. These tables are part of the
EIA Bulletin No.5, BTSC Recommended Practices, as Appendix
D.
With the SRD-1, engineers can verify compliance to these
tables. The SRD-1 is the only stereo decoder easy to calibrate
to BTSC standards.
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.
By using a true RMS detector and a precision window
comparator referenced to a precise 10 volt reference, a system
accuracy of ± 0.03 dB composite level
setting is achieved. Two LED indicators show when the level
is correct. A green LED is visible when the signal is in
the window, and a red one when the level is above the window.
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.
The
level setup is done at ± 25 kHz
deviation using the Bessel null method and thus is not limited
to setup with any specific generator.
Maintains performance over temperature
Most manufacture's skirt the question of a decoder's
BTSC performance over a temperature. That's because the BTSC
encoder/decoder circuitry is notoriously temperature sensitive.
Modulation
Sciences, however, 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
Correct input level is indicated by the front panel LED's.
When only the green LED is lit, the input level is correct.
A true RMS detector reduces the effect of random noise on the
level setting and improves accuracy. A simple Bessel null procedure
sets the modulation to the correct level for alignment.
Operates with Tektronix Demodulators
The SRD-1 needs only a wideband composite signal for operation.
The most common source of that signal is the deviation output
of the Tektronix 1450-1 or 1350 demodulator. The output of
a TV stereo generator can also drive the SRD-1 directly.
Compliance to BTSC certified independently
Modulation Sciences commissioned Radio Techniques, an
independent firm of licensed professional engineers, to test
its SRD-1 Stereo Reference Decoder for BTSC compliance.
Those
tests produced the most extensive characterization of any stereo
decoder on the market; they also proved the laboratory grade
performance of the SRD.
But don't just take our word for it:
A complete copy of the report is available for the asking.
Contact MSI.
Less than the cost of BTSC-capable modulation
monitors
By building an uncompromised decoder without a lot of unnecessary
bells and whistles, the SRD-1 achieves laboratory accuracy
at a modest price--one half to a third less than BTSC-capable
modulation monitors.
Instead of creating an expensive, complex
dedicated modulation monitor, Modulation Sciences knew
that TV stations had a sufficient amount of test equipment
to make accurate measurements and instead needed a decoder
to drive those test instruments. Our design goal was a decoder,
which would be as nearly perfect an audio decoder as possible.
The
SRD-1 successfully achieves these design goals. And the
money your station saves by buying the most accurate decoder
available can be put to good use ensuring that your station
has equally accurate general purpose test equipment.
Simple to test
This test setup provides continuous
performance data on the stereo system. The frequency range
is swept several times per second and the result displayed
on a CRT. This allows viewing the effect of any adjustments
of the stereo generator or transmitter as they are made. Such "real time" displays
of separation, frequency response and crosstalk can be done
with the SRD-1 in either BTSC or equivalent mode.
The SRD-1
is your most accurate assurance of stereo performance and
compliance. No other stereo monitor rivals it.
Typical MTS test setup using SRD-1
The AUDIO TEST SET can be any real-time audio instrument.
A Sound Technology 1510 or 1530 is an inexpensive approach
that provides 1/3 octave data in real time; it also has all
the functions necessary to align stereo tape machines and make
most other stereo audio measurements. Alternate instruments
are Tektronix 715 or 5L4N low frequency spectrum analyzers.
As
an alternative, data may also be plotted on a point-by-point
basis on audio log paper using a conventional audio oscillator
and an AC voltmeter. If this method is used, it is important
that at least 25 points be taken, so no fine detail is lost.
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