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Recently we talked a bit about how to put some logic into your decision making when you are comparing equipment or antenna performance. The topic was the venerable A-B test, using a two-way switch that could be connect first one antenna, then another. The idea behind this kind of testing is to eliminate as many variables as possible so that we are really just comparing the two things that we want to compare. After all, using separate transceivers (each one connected to its own antenna) puts into play the extra variable of radio performance when what we really want to do is compare one antenna to another one. It makes much more sense to use a single radio and an A-B switch with the common side connected to a single radio and the switched outputs each connected to separate antennas.
Now I would like to introduce you to another related concept to help you work your way through troubleshooting. It is called a "decision tree". A decision tree gets its name because it branches out much like a tree. From the main trunk, let's say there are two large branches. From each of those branches there are two more, and so on. At the base of the tree it is easy to see just the trunk, but high up in the air atop the tree there are thousands of branches. The concept of the branching tree can help us to solve problems with our electronic equipment. Decisions must be made logically and empirically, beginning at one point where the symptom of the problem presents itself and is easy to see, much like the trunk of the tree. Sometimes there may be many, many possible causes for that very same symptom -- all of these possible causes are represented by the many branches at the top of the tree. If we look at the top of the tree, we will see a confusing collection of branches, or possible causes to our problem. The idea of the decision tree is to start at the trunk with the most obvious symptom and follow the branches outward and upward until we arrive at the single twig at the top of the tree that is the cause of our problem.
Now, let's see how this works with a problem that most of us have encountered with our radios.
Let's say that we go down to the ham shack in the basement and turn on the HF radio. Oddly enough, nothing seems to happen; no sound comes out of the speaker. Of course with a problem like this there can be many possible causes. Putting the idea of the decision tree to work for us can save time and effort as we work our way logically toward a solution to the problem.
1. Did the radio power up?
If the answer is yes, proceed to number two.
If the answer is no, we follow this branch:
Is the power switch in the on position?
If the answer is no, turn on the power switch and your problem is solved.
If the answer is yes, you now have another branch to follow:
Is the radio getting power from the power supply?
If the answer is no, you need to follow another branch:
Is the power supply is turned on?
If the answer is no, turn on the power supply and the power is now available to the radio and you may proceed to operate normally.
If the answer is yes, you are off to the next branch:
Is the power supply plugged into a live AC outlet?
If the answer is no, you need to plug it in or find another outlet that is live, then proceed to operate normally.
If the answer is yes, you need to check the fuse or circuit breaker in the power supply and proceed along a line of determining a problem with the supply rather than the radio.
2. Is the audio gain turned up high enough to hear sound?
If the answer is no, turn up the gain and proceed to operate normally.
If the answer is yes, you are off to the next branch:
Is there any sound at all when you listen closely, such as a weak hiss?
If the answer is no, you will want to follow a line of checking external speaker connections, whether headphones have been left plugged in by mistake, and so on. Several more branches can be followed here - you get the idea.
If the answer is yes, you will want to follow several other branches that will include checking the RF gain control, the antenna connection, any tuners or other accessories in the feedline, and so on.
As you can see, a decision tree can be quite long and branching, even for a simple problem. However, the idea is to begin logically with the things that are easiest to check and most likely to be the cause of the problem. It certainly wouldn't do to immediately run outside and check the antenna if you didn't hear sound from the radio. Audio gain controls that are turned down, squelch controls that are turned up too high, RF gain controls that have been turned way down, or an antenna switch that is in the wrong position are all more likely causes of the problem. Furthermore, you wouldn't want to start working on repairing your transceiver if a circuit breaker in your house's main breaker box has tripped, causing the outlet into which your power supply is plugged to be dead. It is all about following a logical, thoughtful path in problem solving.
Believe me, this is not something that new ham radio operators -- and even some with extra class licenses -- always know how to do. Logical troubleshooting is something that can be learned by experience. Sometimes equipment repair manuals include graphical decision trees to help technicians working at the service department proceed through the diagnostic process and a logical and efficient manner. These days, software can help us make decisions as well, but I would like to see our Handiham members be as independent and self-sufficient in troubleshooting basic problems as possible. At the upcoming Minnesota radio camp we will be considering how to solve basic problems in the ham shack. Practicing this skill makes us all more independent and ultimately better operators. After all, amateur radio is a technical activity, and we should be able to do some basic troubleshooting.
For Handiham World, I'm...
Patrick Tice, wa0tda@arrl.net
