This is one of the clearest explanations I have seen of the issue. Thanks Erik.
73 Bill AE6JV On 9/2/18 at 5:53 PM, ebasil...@cox.net (Erik Basilier) wrote: > As Jim K9YC has pointed out in his writeup on baluns etc, there is a > threshold effect when one applies a choke to reduce common mode current. The > current is determined by driving voltage and total (complex) series > impedance. The choke RF impedance will have a reactive as well as a > resistive component, and so does the circuit before the choke is applied. > The reactances may be of opposite signs and cancel out, in which case adding > the choke may actually make it easier for the common mode current to flow. > It is easy to think that one can add a marginal choke and look for a small > improvement as a reliable indication that a good choke will be worth the > investment or not. Wrong! Only then the choke tried has high enough > impedance to dominate the circuit can one judge whether whether adding > chokes helps. Also, adding the perfect choke near the antenna feed point is > not likely completely to eliminate common mode RF current at the rig end of > the cable. For common mode purposes, the perfect choke acts effectively to > disconnect the outside of the coax from the antenna, but that metal is still > there, close to the antenna, and it will be part of the antenna system as a > parasitic antenna element, affect the radiation pattern, and carry > substantial RF current. > 73, > Erik K7TV ----------------------------------------------------------------------- Bill Frantz | There's nothing so clear as | Periwinkle (408)356-8506 | a design you haven't written | 16345 Englewood Ave www.pwpconsult.com | down. - Dean Tribble | Los Gatos, CA 95032 ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
