If it's of any use to anyone, here I described a simple 40 dB / 20W attenuator I once built
You can also convert a QRP Labs or QRP Guys dummyload into an attenuator that way, it may not be the "perfect" 50 Ohm IN/OUT attenuator, but surely good enough to test a QRP rig. Even with ordinary resistors, it will be useable in the HF range.
Another option is to build a "power sampler", see a link in the post mentioned above.
As for that "better" video on Youtube that Evan mentioned.
It shows the problems all right, but it does NOT explain it, the maker of that video cleary missed some points.
"... it goes up and down ... some weird filter ... " huh ?
The simple explanation is that the NanoVNA is limited to 101 points, so runs over the spectrum in too coarse steps, missing several signals if they are not on one of those 101 frequencies. Reducing the sweep range may show more signals, but still miss some.
And nothing weird about the IF filter, but the IF of the NanoVNA is at 5 kHz, so you will see an image signal at 10 kHz offset.
So the NanoVNA is not a spectrum analyzer, but yes, it can be used as a very crude signal monitor ... if you know what you're doing, and don't expect too much.
73,
Luc ON7DQ
