If I get in really close, I can see some low-level ADS-B signals. If you look at the right side of the first two plots, you’ll see underlined MAX HOLD A – the spectrum analyzer is tracking the maximum level at each point along the spectrum. The first two plots show data captured over probably tens of seconds. In that period, at those display settings, ADS-B is a little bump down in the weeds. And yes, those transmissions are very short, on the order of milliseconds – I’m sure a number of the folks on this board know the durations.
Remember that most SDR dongles, such as R820T dongles, provide gain up to 40 dB.
With fancier/newer spectrum analyzers, you can get data demod packages that let you capture and display data.
My spectrum analyzer is at the other end of my lab from where the antenna feed for the SDRs is – I’ll dig up a long jumper cable tomorrow and see what’s up at the output of one of the SAW filters.
–bob k6rtm