On 1/14/2019 9:02 AM, Barry wrote:
The simple answer is that the common mode chokes available to hams are of the unbalanced type.
Huh? We're hams -- we're not limited to products we can buy! And we can build far better than we can buy. In 2010, I published the design for a common mode choke to cover the HF bands using a pair of #12 THHN wound on a 2.4-in o.d. #31 toroid. k9yc.com/2018Cookbook.pdf has dozens of designs using THHN, teflon pairs, and RG400. These chokes are fairly easy to wind, and all can be built for less than about $35, including connectors.
A member of our contest club is building a serious contest station, and asked me to measure a "balun" from a well-known manufacturer. It came in a nice weatherproof non-metallic enclosure, and was nicely made. But it looked NOTHING like the data sheet that WAS on the website at the time (and which has been removed since I showed my data to a few engineering colleagues, one of whom obviously asked the mfr about it.)
The problem with choking a two-wire feedline is NOT one of balance -- if it's a good choke, the choke takes "balance" out of the equation. What matters is dissipation in the choke due to excessive voltage or current that is present because the antenna is not matched to the line.
73, Jim K9YC ______________________________________________________________ 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 Message delivered to [email protected]
