Depending upon why you are doing the measurement and what it is you are measuring, sometimes you want to see the >20MHz noise especially if it is for a design that has to go through EMC compliance testing. A spectrum analyser and a near field test set and an LPDA in an anechoic chamber are very useful to have around, albeit spectrum analysers are damned expensive. It used to be the world was only interested in emissions above 30MHz, but these days, it is almost DC to daylight. Which is good because of the amount of HF EMI in Melbourne cities is now beyond the joke - a lot of it due to illegal imports from China.