WiNRADiO G69DDC User’s Guide
Noise Blanker
The
Noise Blanker
can be used for removal of random high-level noise-spikes
resulting from atmospheric effects and man-made interference.
There are two types of noise blankers available, one using the
Short Time
DDC Averaging
method and another using the
ADC Input Threshold
method.
The
Short Time DDC averaging
method is based upon comparing the
instantaneous signal level at the DDC output (demodulator input) to a short-
time exponential average. If the instantaneous level exceeds the short-time
average, these samples will be replaced with zeros.
With the
ADC Input threshold
method, the blanking effect occurs much
earlier in the signal processing chain: The signal samples arriving from the
ADC are compared to a threshold value, and if greater, then these samples
are zeroed.
The
Short Time DDC averaging
method is preferable and will yield
improvement in most cases of atmospheric or man-made interference. It is
activated by pressing the
Enable DDC averaging
button located under the
Noise Blanker
tab. If the instantaneous signal level at the input of the
demodulator exceeds the short-time average level by a user-adjustable
percentage amount, these signal samples will be replaced by zero values.
The
Sample Excess
setting should be adjusted as a compromise between the
noise blanking effect and the minimum acceptable distortion of the wanted
signal. The current value of the signal excess above the short-time average is
indicated in the associated display, to assist with the adjustment.
The
ADC Input threshold
method is activated by pressing the
Enable ADC
threshold
button. If the input at the ADC exceeds that defined by the
ADC
threshold
control, the ADC input will be blanked. The current ADC level is
shown in the adjacent display to help with this adjustment. The maximum level
(100%) corresponds to the entire input range of the ADC.
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