If a GWInstek GSP-730 spectrum analyzer becomes unresponsive this is probably because of it trying to restore a connection via USB interrupted by a last shutdown when it was connected to a PC. To return it back to live just connect it to a PC before powering on and disconnect from a PC before switching it off.
Showing posts with label Signals and Systems. Show all posts
Showing posts with label Signals and Systems. Show all posts
Wednesday, July 9, 2014
Saturday, April 5, 2014
An ideal filter is hard to build
Why is it hard to build an ideal digital filter, e.g. an ideal lowpass band filter
From the mathematical point of view such a filter has an infinite spectrum in the time domain, i.e. it is not casual. What does it mean for software or hardware implementation? Consider two close frequencies one below cutoff frequency f and one above it, f-d and f+d respectively, where d is an infinitesimal and the filter must remove the second from its output. If a digital filter performs sampling of an input signal then for such close frequencies it would see the same values for an infinite time as a difference is below its resolution threshold defined by its internal ALU implementation, the filter will see one frequency
and it will take an infinite time as d approaches zero before both signals split up far enough so the filter recognises the difference, i.e. you must have an infinite delay in a filter.
From the mathematical point of view such a filter has an infinite spectrum in the time domain, i.e. it is not casual. What does it mean for software or hardware implementation? Consider two close frequencies one below cutoff frequency f and one above it, f-d and f+d respectively, where d is an infinitesimal and the filter must remove the second from its output. If a digital filter performs sampling of an input signal then for such close frequencies it would see the same values for an infinite time as a difference is below its resolution threshold defined by its internal ALU implementation, the filter will see one frequency
Monday, March 17, 2014
A spectrum of a 2.4 GHz WiFi
Just for fun, below is a picture for a 2.4 GHz WiFi spectrum captured by a GWInstek-730 spectrum analyzer at my house
The bar lines don't represent WiFi channels, the channels are much wider - at least 20 MHz, these bar lines is just a feature of the sweep-tuned spectrum analyzer capturing fast changing signal. I believe that GWInstek-730 is an analogue sweep-tuned analyzer that does not perform DFT / FFT of a signal.
The bar lines don't represent WiFi channels, the channels are much wider - at least 20 MHz, these bar lines is just a feature of the sweep-tuned spectrum analyzer capturing fast changing signal. I believe that GWInstek-730 is an analogue sweep-tuned analyzer that does not perform DFT / FFT of a signal.
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