Hi Felipe
It works like a voltage divider where the impedance to ground should be lower as possible to give you more attenuation like 1k/500ohms versus 1K/5 ohms divider. You should use the choke near a good ground before entering the station. If you switch box have a good ground it’s a good place to install it. More turns better, but it is limited by the diameter of the coaxial cable, like RG58/RG142 allows 12 to14 turns. RG213 only 8 turns. Jim K9YC and a fantastic documentation about chokes. Please read this document http://audiosystemsgroup.com/RFI-Ham.pdf You will be a specialist after reading this guide. Regards JC N4IS From: Filipe Lopes [mailto:ct1...@gmail.com] Sent: Monday, October 12, 2015 9:52 AM To: JC <n...@comcast.net> Cc: topBand <topband@contesting.com> Subject: Re: Topband: Commond mode choke for Beverage Hello JC, Thanks for your answer. I just ordered a few 2631803802 and 5943003801 from mouser. With these ferrites I ask the same question, should I put the choke close to the 9:1 Balun or near the switching box and how many turns? some bevs have the feed point at +- 60m away from the switching box. 73's Filipe Lopes CT1ILT - CR6K F4VPX - TM3M 2015-10-12 15:40 GMT+02:00 JC <n...@comcast.net <mailto:n...@comcast.net> >: Hi Filipe Zero , you should use material #31 or #77 , The core you have is not good for low bands. JC N4IS -----Original Message----- From: Topband [mailto:topband-boun...@contesting.com <mailto:topband-boun...@contesting.com> ] On Behalf Of Filipe Lopes Sent: Monday, October 12, 2015 8:46 AM To: topBand <topband@contesting.com <mailto:topband@contesting.com> > Subject: Topband: Commond mode choke for Beverage Hi guys, I am about to add a common mode choke to isolate the antenna from its feedline to each of my beverages and I only have FT240-61 ferrites. My question is how many turns should I do on the ferrite using RG58 (all my bevs are fed with RG58). Also should I put the choke near the 9:1 balun or near my bev switching box? Thanks in advance. 73's Filipe Lopes CT1ILT - CR6K F4VPX - TM3M _________________ Topband Reflector Archives - http://www.contesting.com/_topband _________________ Topband Reflector Archives - http://www.contesting.com/_topband