--- In [email protected], "Jeff DePolo" <[EMAIL PROTECTED]> wrote:
> > Do you have any thoughts on why or how a well designed Z > > match could produce cable > > radiation? > > For the feedline to radiate, there would have to be currents flowing on the > shield. It would seem to me the only way to get that to happen would be if > there was an imperfect shield connection at the mating connector at one end > or the other. Most Z-matchers I've dissected use a length of wire as an L, > with shunt trimmer caps. Assuming the enclosure itself is bonded well to > the connectors at either end, I can't come up with a good reason why such a > device inserted in a transmission line would cause shield currents to flow > absent a connector issue. > > --- Jeff How about an instance in which there's a thru hole ground connection from the inside to the outside of the case. e.g. a bolt from a floating pcb ground plane or a capacitor that protrudes thru the case & is nutted on the outside of the case. If that bolt is not well bonded to the inside of the case, it can carry rf current to the outside that is not in phase with current at the connectorized ends. As the length of the bolt or rivet increases, so does the Z & phase difference between the pcb groundplane & the insides & outside of the case. Now you have at least 3 circulating currents. The pcb groundplane itself(end to end), the pcb thru the bolt to the inside of the case & last, the unintended pcb thru the poorly bonded bolt to the outside of the case. Yes, I do enjoy playing Devil's Advocate. Hey! It's a slow Sunday.
