Measurements are Alfa and Omega of radio design. They are key to all understanding, designer's third eye. Although this is the Tech Note, I am not going to be too technical here. I will try to discuss some important concepts using just simple English and almost no formulas. There are a lot of methods and instruments, but we will start with:

Step attenuator
Maybe the single most useful instrument in radio lab is step attenuator. Never-ending discussions about the best antennas, noise figures, gain, power amplifiers - his majesty dB (decibel) is everywhere. But how many of us know how much is 1 dB, or 5 dB, or 60 dB? I am not talking about definitions here, I am talking about the feeling of a decibel. Imagine that you have a dipole antenna and enjoy working QRP. But for the next big contest you decided to improve your antenna system, to compete for some top contest place. So, you can put antenna with some gain, say 5 dB. How much is that? I can explain it here using some poetic expressions, or examples with S-units, or some hard to read fancy looking formulas, but really the best way is to built attenuator and find for yourself. And you will be surprised, as I did. Good attenuator is not expensive instrument, nor complicated to built. And I promise, you will use it a lot. We'll be back to attenuators soon, but just for now I can tell you - 3 dB (double power) is detectable by ear, but not much more than that. 10 dB really makes a difference.

Signal generator(s)
OK, we have our DUT (Device Under Test), and attenuator, now we need some signal to test our device. What kind of signal? It depends what we are going to measure. Unless we are measuring phase noise, the most important thing we want to know about our signal is it's amplitude. Also we need signal of defined frequency, and with the ability to change this frequency. For MDS (Minimum Discernible Signal), IP and Dynamic Range measurement output level of our signal generator should be about -20 dBm. It is a signal that is 20 dB (100 times) weaker than 1 mW, or 0,01 mW. It is fairly strong signal (S9 + 53dB) for receiver testing. Step attenuator of 20+20+20+20+20+10+5+3+2+1dB together with such signal generator can generate all the signals from weakest to strongest we can expect in our radio. For MDS measurement we will need only one signal generator, but for dynamic range testing we need two of them. It is fascinating how much confidence a designer can get with just two of these instruments.

.. to be continued and expanded