Power Seduction, Part 97 — by Jim Goudie, AF3Z
This is not part 97 in a long series of articles. Rather, it’s about how power can be seductive, and how we often ignore this section of Part 97 of the Amateur Radio Service rules:
“§97.313 Transmitter power standards. (a) An amateur station must use the minimum transmitter power necessary to carry out the desired communications.”
Honestly, that rule doesn’t always work. Some equipment can only be set at high or low power. On 2m FM, ‘low’ power may be higher than needed for a good QSO but your radio won’t go any lower. On HF, the amount of power needed can be changing from moment to moment; it’s not always easy to know how much power you need.
So this rule can be hard to follow and to enforce, but ‘the spirit’ of the rule is good. Without nit picking and getting legalistic about it, keeping output power at a reasonably low level helps to reduce interference (QRM) and maximize the good use and enjoyment of the amateur radio bands.
That’s the easy part. This is all complicated by the fact that power is seductive, and not just in politics. I enjoy running QRP CW, at times. In a recent two-hour QRP CW contest, I ran about 1.3 watts, worked 9 states, and got signal reports S6, S7… I guess I could have reduced my output but I didn’t! Other times when I’m not required to run low power for a QRP activity I tend to feel that I need more power which often isn’t true. I run mostly HF CW. With SSB or AM more power will be needed; digital modes get through with less. My point is that it’s often tempting to run more power than needed.
Where we can get fooled is thinking that power is more powerful than it is. Yes, if your signal is marginal, a little more power may make the difference and get you out of the noise. Otherwise, a modest power increase may not help as much as you hope.
Doubling your power output doesn’t make your signal twice as loud! For extra credit, read up on logarithms and decibels, because the relationship between the power level and the loudness we hear is not linear, it’s ‘logarithmic.’
Doubling your power yields a 3 db increase. That is just enough to start noticing that the signal is a bit louder; less than 1 S unit; nowhere near twice as loud!. S meters vary, but it may take 5 or 6 db to get an increase of 1 S unit. Crank up your power 10 times— 50 to 500 w, 100 to 1,000 w — and that gets you about 2 S units (10 db) on the meter.
So, think clearly; power can be seductive as well as helpful. Getting the power question right helps us have effective stations while avoiding unnecessary QRM and expense. §97.313 may turn out to be a mentor and friend we do well not to ignore.