Rack-Mount RDMS
TM
Telemetry Receiver
70
Quasonix, Inc.
Figure 125: Mod Scaling Menu, Mod Scale Index Selection
A dialog screen displays prompting the operator to enter a new modulation scale index using the rack’s front panel
numeric keypad. The Index Entry screen is shown in Figure 126. When the new value is entered, press the Enter key
on the keypad.
Figure 126: Modulation Scale Index Entry Screen
To clear any locked modulation scale index number, go to the Main Menu and toggle the Mod Scaling option back
to Tracking. After Mod Scaling is set to Tracking, the modulation index follows the receiver's present estimate of
the mod index.
4.1.5.18.2 Hold Threshold
When Mod Scaling is in Tracking mode, the modulation index estimate becomes poorer as the signal-to-noise ratio
(SNR) decreases (that is, as the received signal gets weak). This in turn negatively impacts demodulation
performance, making bit errors more likely than they would be if the modulation index were known a priori. The
purpose of the Hold Threshold is to set an SNR level (technically Eb/N0* level) below which the modulation index
estimate will hold rather than track, so it does not get perturbed by noise.
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Eb/N0 is the ratio of signal energy per bit (Eb) to noise energy spectral density (N0), which is sometimes
referred to as “SNR per bit”.