EMRFD Message Archive 12620
Message Date From Subject 12620 2016-04-08 09:45:57 iq_rx Troubleshooting
Interesting topic...but different from experimental methods in RF design. Some of us have had the privilege of working with truly gifted folks who can encounter a complex system that is misbehaving in some way, zero in of some possible defect, devise an experiment to quickly test that hypothesis, ask a few questions, and make one minor change to rapidly get things working perfectly again. In electronics we call those folks "technicians," and if the system is a person we call those folks "medical doctors."
People with that skill set are a treasure, and we don't appreciate that ability to locate and remove a needle in the haystack that is causing some problem, in an incredibly complex system that used to work, nearly enough.
But that is different from a scientific approach to design. Designers spend their time on things that haven't yet worked, and the first rule of experimental science is to carefully design the experiment so that everything else is a fully functioning reference. A new system is built up piece by piece, with every piece tested and working before the next part is added. Once a full system is up and running, further design work may involve experimenting with individual sections and doing substitution experiments, the standard scientific method of comparing an experiment with a control. In an experimental approach to design, the experiment may be a new filter, mixer, amplifier--but it isn't the whole receiver.
In my opinion, the single most eloquent description of the experimental approach to receiver design is Wes Hayward's two part QST series describing "The Progressive Receiver." Hayward's entire approach to radio engineering applies the most fundamental of scientific methods: start with something simple that works, that you understand. Add a piece, observe and think about what you hear. Don't move on until you understand the simple version. Try a different piece and choose the one you like best. Use it on the air until you are happy with its performance. Then add another experimental piece. It takes Wes years to evolve a receiver into something that satisfies his imagined standards for some particular application, and he's made maybe a thousand CW contacts along the way.
The beauty of this approach to design is that the simplest receivers: a mixer, oscillator, and audio amplifier, don't require any test equipment other than an antenna and headphones. It really helps to have another receiver so you can listen to the oscillator and switch antennas so you know what signals you should hear. Wes and I both started playing with new, simple receivers in our paper route years, when we didn't own any test equipment other than a volt meter.
Wes and I have both observed that many accomplished designers of the most complex, high performance receiver systems are also unusually experienced with the simplest receivers--direct conversion and crystal sets. The simple receiver is the starting point that already works. The experimental part that requires "troubleshooting" is a simple addition that might make an improvement in performance. The experimental part is often simple enough that the existing working receiver, antenna, and ears are the primary test equipment.
I hope that helps.