Preparation |
Real-Time Spectrum Analysis
8
REAL-TIME SPECTRUM ANALYSIS
2.6
One of the issues with the standard sweep mode is the “blind time” between each trace. Blind time
refers to the time between spectrum sampling. During this time, we are processing the last capture, or
viewing the data. During this time it is possible to miss an event. The picture below shows a missed event
in green.
In this image we see an event missed due to the blind time between spectrum sampling. With Real-Time
spectrum analysis we can prevent this and capture ALL possible events.
The BB60C is capable of streaming the full IF bandwidth with no time gaps. If we limit our spans to the
maximum instantaneous bandwidth we can now process every spectrum sample for our resulting trace.
The BB60C performs overlapping FFTs at an overlapping rate of 50%, covering each point of data with 2
FFTs. We take the resulting FFTs and min/max or average them into a final returned trace. The number
of FFT results merged depends on Real-Time Accumulation and the RBW.
The minimum signal duration to guarantee the same amplitude as a CW signal (i.e. 100% probability of
intercept) in real-time analysis mode is a function of the resolution bandwidth selected, and is equal
to1.5 times the FFT interval. The FFT interval is approximately 2 / RBW, so for a 631 kHz RBW, this works
out to about 4 microseconds. Lower RBWs will require proportionally longer signal duration. However,
signals of even ¼ this duration will be displayed only 2-3 dB down.
See the Spike Software manual for further information on Real-time mode.