I have very little knowledge of DSP, so would appreciate if anyone here can help out.
One of our club members M0KGW suggested that the RBW of the tinySA or homebrew simpleSA could be improved using convolution.
The idea is if you know the response of the SI4432 FIR filters, (we can measure this) then by sampling at smaller frequency step increments and using convolution then it should be possible to recover some of the information to get improved resolution bandwidth (RBW).? Improved RBW is desirable for measuring intermodulation of transmitters.
Consider say two signals at close spacing, say 1kHz apart.? The SI4432 has a minimum RBW of 2.6kHz so by stepping at say 2kHz intervals it is not possible to pull out these two signals.? If a smaller frequency step is used, then as the signals come in and out of the filter passband the RSSI value will change - the RSSI at each frequency step will be the sum of the filter response for each signal.? Given the frequency response of the filters it should be possible to extract the two signals using convolution in the frequency domain.
45 years ago I might have been able to work out the maths for this, sadly no longer.? Also sad to say I had not even heard of convolution before M0KGW mentioned it.
Is this idea practical and if so how to go about coding it?? I would certainly like to give it a go and see how it works in practice.
73
Dave M0WID
