Deviser S7200 User Manual page 94

Part II: Settings and Measurements
6-17.2 Signal Shoulder Test
When the digital TV signal is amplified, the intermodulation output outside the channel is an approximate
continuous spectrum. The continuous spectrum outside the channel generates "shoulder" effects, called
the band shoulder. The "shoulder ratio" is the ratio of the power level at the center frequency to that of a
single point deviating from the center frequency outside the carrier. For example, a Chinese TV channel
bandwidth of 8MHz will have a band shoulder ratio (measured in dBc) of:
Power amplifiers are the main nonlinear component in transmitters used for terrestrial digital broadcasting.
Their efficiency and linearity are inversely related: a high-efficiency power amplifier will generally exhibit
strong nonlinearity, which causes signal distortion. The resultant in-band/out-band interference is reflected
on the spectrum as the shoulder ratio difference. Shoulder ratio is a key technical specification of digital TV
RF output; it expresses the linear level of the digital TV transmitter power amplifier.
As shown below, a signal shoulder measurement requires a transport stream source, a transmitter, and a
spectrum analyzer. For terrestrial digital broadcasting, transmitter shoulder performance is ≤ -36dBc.
An alternative measurement method employs a terrestrial digital TV actuator instead of a transmitter. This
measurement's performance spec is ≤ -48dBc.
Button Operation
[GAIN>] Set attenuation to Auto/Manual. In Manual mode, use ATT+/- to set attenuation.
[FR-OFFSET] Set deviation from center frequency (4.2 MHz in above example). Range 1-5 MHz.
[LIMIT>] Set pass/fail limit on test. Preset limit for Xmitter (transmitter) is ≤ -36dBc; preset limit for
Exciter (actuator) is ≤ -48dBc. Otherwise, choose User Def to set a custom limit value.
[HOLD] Pauses the measurement. Press again to resume.
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