What's the fundamental measurement you make regularly but are still challenged by?
Mine, RF Power with a Spectrum Analyser.
Even though frequency-domain measurement of RF power is one of the most basic measurements performed by traditional spectrum analyzers and modern vector signal analyzers unless I apply appropriate measurement techniques to each set up or device I can get significant errors.
It's not simple today and it's not tomorrow so always an enjoyable challenge to get teh set up right and the errors minimised
