Many banana plugs and jacks use nylon insulation which is a *terrible* RF insulator. Nylon is hygroscopic (absorbs moisture) so its insulating properties are highly dependent upon the relative humidity.
Running 15 watts into an end-fed wire I literally melted a banana jack that looks just like those shown at the top of the page here: http://www.oselectronics.com/ose_p111.htm In just a few seconds of sending, I smelled hot plastic and saw smoke rising as the insulation sagged. As it happened, I had a voltage loop (point of high RF voltage) at the rig on that band and it caused a quick and total failure. But even at voltages below that which caused failure, part of the RF was being converted into heat instead of electromagnetic waves. All of the Pomona hardware that I've seen uses polycarbonate insulation. This is superior, tough stuff! Pomona makes these adapters for use with test equipment at very low voltage levels. The popular 1296 that Matt, K7OE mentioned, is rated to 500 vac max (see data sheet at http://tinyurl.com/7mca5). They don't publish dielectric info or mention their losses at RF, but that sounds adequate for RF power levels up to some tens of watts into a high impedance (1,000-ohm) load. Of course lower impedances mean lower voltages. I still use nylon banana plugs and jacks for single wire and open wire feeder connections, even at QRO power levels, but I never rely on the nylon for insulation. The jacks are always mounted in an acrylic or polycarbonate insulating panel with ample spaces between them. Ron AC7AC _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
