Mike Dietrich wrote: > What is the best way(hookup) to "test" cables like these to see if they > are resonant on a particular freq? > With or without the coupling loops attached etc. for duplexers say
The technique I've seen used and participated in is to test the entire section of the duplexer as a unit (with appropriate 50 ohm loads on the other side) using a tracking generator/spectrum analyzer, after getting the individual cans in tune. If connecting multiple cans and testing through them "pulls" the tuning of the cans (there are multiple "humps" in the image shown), the cable lengths are wrong. When the lengths are correct, two cans "add" to make a steeper/taller pass... for example. (It's easier to see this than to describe it in e-mail. Maybe someone will send some screen-shots of what it looks like someday... I've tried taking photos of my IFR 1500 with my cheap digital camera (4MP point-and-shoot Nikon) and it just doesn't look right. Someone with an HP service monitor would have a bigger screen and along with a good camera could probably capture what it looks like better. This technique is a "wholistic" approach to it, I suppose you could call it. You're shooting for the length that ends up looking the best after tuning the individual cans, and locking them down. As long as everything else has proper 50 ohm loads on everything that's not under test. Also always a good idea to use a 6dB 50 ohm pads between the signal generator and the device under test... of course. Normal practice... just in case. (Depending on the test gear and the device being tested, things can get really squirrelly if the test gear is expecting a 50 ohm load and doesn't have one...) It includes the loops this way, of course... because the end-result you're shooting for is that particular duplexer to work at your desired frequency. I hear this process is even nicer to do with a Vector Network Analyzer, but I've never even seen such a beast, let alone used one. Nate WY0X
