Originally Posted by
India Four Two
FP, Is there a specification for the filter slopes (dB/octave) of an aeronautical VHF channel?
Unfortunately I can't answer that question directly, my post was largely from first principles and it's been many years since I worked on this sort of thing. A quick search brought up a FAA AC which wasn't all that useful, I suspect the quickest way of getting some idea might be to look at the specs of modern transceiver - Icom for example says "Selectivity More than 7.5 kHz/-6 dB, Less than 25 kHz/-60 dB", but what - if anything - is mandated I'm not sure. Otherwise, with luck, an avionics person might pop up with the answer - although I doubt it's the sort of thing many will have come across let alone needed to know.
Otherwise good to hear you're familiar with filters, one is never sure of the audience when spouting off about things here so tend to over-explain or over-simplify sometimes...
Re your field of expertise, FWIW I developed a triggered XYZ analytical seismometer for assessing and displaying building responses during earthquakes, about 5 years ago. This used FFT + Hanning filter, converted the time domain data into the frequency domain, integrated as necessary then delivered the plotted results to those that wanted to know. I never quite got the displacement calcs right so if you're an Omega arithmetic guru I'd be pleased to hear from you!
FP.