1:1 baluns are dead easy to make: simply wind a few turns of the antenna end of your coax feeder around a suitable toroid core before connecting it to your balanced antenna. I use the FT241 cores from Amidon Associates, the "k" type for 160-40m bands or "61" mix for the higher HF bands. I can easily get 10 turns of RG58 coax on a core, and these seem to work nicely for me [I don't have the knowledge, test gear or patience to test them on the bench, but depend on Mr Sevick's advice in his book.] I've had no problems running our legal limit of 500W into these.
4:1 baluns require a just bit more work. These are made by winding a bifilar coil using two tightly-strapped wires of the appropriate size and type on a suitable core - a chunky T400A2 powdered iron core in my QRO balun (capable of well over the legal limit I'm sure), with an SO239 connector for the coax. All my baluns use watertight plastic boxes with rubber gaskets to seal their lids, stainless-steel hardware for the antenna connections (S/S wing nuts make them much easier to connect up antennas in the field), and some care to ensure they remain watertight in use (e.g. I use superglue to wick into the gaps and seal both SO239s and antenna connections to the case, plus self-amalgamating rubber tape on any PL259-SO239 connections with a layer of ordinary electrical tape over the outside to cut down UV damage to the rubber). For LF dipoles that will put a lot of stress on the center connections, I use an army-surplus ceramic open wire feeder spreader for strain relief on the antenna wire, using tie-wraps to hold the spreader to the box through the box corner mounting holes which don't penetrate the sealed section, at least in the boxes I can buy here. Even buying everything new and importing the cores from the US, they are *much* cheaper than any commercial units of similar power-handling capacity that I can obtain, here in ZL anyway. As a very happy customer, I have no hesitation in recommending Amidon www.AmidonCorp.com There are photos etc. on my site at http://www.g4ifb.com/html/homebrew.html#Baluns and I'd be happy to answer any queries as best I can. 73, Gary ZL2iFB ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
