Excellent points, Jeff, and well taken. Too many subtle interactions for a concise solution.
Still, some night in the near future when things are running smoothly and all we're doing is babysitting things, I'll run some tests with the VNA and see if measuring the XL of the loop and subtracting it from the cable length helps determine a closer empirical starting point. Fiddling with these old cavities and testing them on the VNA at work has been a valuable learning experience. Like many people, I had never really applied the things I've read about the Smith chart to real life. Although I'd made feeble attempts to follow the Smith chart examples in Wilfred Caron's book, and I'd filled up sheets and sheets of notebook paper with complex equations trying to comprehend the math only to find a procedural error in the algebra somewhere that threw things out of whack, it was hard for me to truly get a "feel", that is, gain enough familiarity with the process to develop an instinct to it. But in working with the VNA I quickly found that the Smith function could tell an elegant story. I got immediate visual feedback to my adjustments and experiments, and it all confirmed the principals that I'd been reading about for years. Great fun! (I admit it, I'm a nerd.) I wish I had $15k to buy one of my own, but I'm afraid the house needs siding, gutters, and roof... Thanks again, Brad KB9BPF --- In [email protected], "Jeff DePolo" <[EMAIL PROTECTED]> wrote: > > The problem is that the XL of the loop in free space (unloaded) really > doesn't really tell you anything. The loop is a coupling element; it's not > just a series inductor. Its effect in the circuit will vary with rotation, > cavity resonant frequency, load Z on the opposite port, etc. It's really > not as simple as you'd hope it would be. It it were, I'd have a spreadsheet > that tells me everything I need to know without having to resort to line > stretchers and a rack of dangling test cables... > > --- Jeff WN3A >
