I've had such good results with my HF319 mag loop antenna that I decided to put one together for 10, 12 & 15 meters. Sadly, it doesn't work at all on any of those bands, and only tunes slightly on 30m & 40m. Not sure where I went wrong, but it's back to the ol' drawing board...

@N2PAS Have a good look at this loop, which is for 12-10m. It's very small - only around 1m circumference. Notice the coupling mechanism - no primary loop. The cap is a 10-50pF variable. If you use too high a value cap, it makes it tougher to tune (smaller steps mean bigger changes in value). You can tune by hand but it's tough without a drive reducer of at least 6:1, preferably a 10:1 or higher.

@MW1CFN Excellent! Thanks for the guidance. I'm taking the whole thing apart and starting from scratch. I've only got the one capacitor, 10-150pF, so I'll start by trimming the loop and see where that takes me.

@N2PAS No worries. The cap is a good range for a multi-band loop. For reference, my upper bands HF loop is ~56 inches in circumference. There are many ways to feed/make/tune/match a loop, so taking things apart and going again is entirely normal. This post may or may not help - it's but one way to feed a loop: https://mw1cfnradio.blogspot.com/2015/11/magloop-matching.html

@MW1CFN The blog article links to the online calculator I used to fabricate the antenna components, but the #nanovna tells a different tale. You were spot on about the capacitor--it's nearly impossible to dial it in by hand, and the loop itself appears to have little to no resonance in the desired frequencies. Guess I'll be looking for some kind of servo with gear reduction and a way to determine the correct loop dimensions. If nothing else, it's a great scientific adventure!