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Comment by Nrsolis | Hacker News Reader

Agree.

Amateur radio operators have dummy loads and SWR meters to make sure that the signal they are putting out isn't stomping on some other critical portion of the RF band. Experimentation is a good thing, but this is the equivalent of someone being disturbingly careless experimenting with chemicals in their home "lab." The chance you could cause a serious problem with contamination for your neighbors is small but definitely non-zero.

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I fail to see how a dummy load and a SWR meter will help to make sure you don't disturb other (portions of) RF band(s). To assess this you must look into the spectral purity of your signal. You do this with a spectrum analyzer (or equivalent). The SA is already 50 Ohms terminated so you at most need attenuators for your transmitter. The SWR meter will tell you if your transmitter is matched to your antenna. If not you might kill the final stage of your transmitter. SWR doesn't tell you something about radiating unwanted frequencies.

You are correct about the SWR only measuring the matching of your output to the antenna. But consider this: a signal with lots of harmonics (read: outside of your band intended RF signals) is going to make a 1:1 SWR match harder to achieve. If you've cut your antenna to the right length and you're not getting close to the match you need, something is wrong. It's a rough measurement to be sure, but decent in a pinch.

That said, you should always use a dummy load when working with a new transmitter project. SA is always a good idea, but I've been in a lot of shacks that didn't have one.

Of course, this guy used a FM radio to check his signal. He should have used a scanner and checked out the multiples of his center freq.

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