I got this unbalanced common-mode choke from Amateur Radio Supplies. It completely clobbered all of the "bite" I was getting in the shack, and is keeping stray RF out of my bench computer. I got it when I was having trouble with the keyboard I had connected to my PX3 -- when I transmitted CW or PSK31, the RF would cause random characters to get stuffed into the keyboard buffer, and the transmission wouldn't stop until I stopped it manually. It helped, but the way I finally got around it was by using a 2.5ghz non-Bluetooth wireless keyboard for the PX3. Any wired keyboard I used would result in garbage in the transmission as the RF induced current in the keyboard cable.
https://www.amateurradiosupplies.com/product-p/iso-max.htm 73, Gwen, NG3P On Mon, Jan 14, 2019 at 12:03 PM Barry <[email protected]> wrote: > Vic, > The simple answer is that the common mode chokes available to hams > are of the unbalanced type. That means they are designed to be > unbalanced in to unbalanced out. Some companies make baluns that are > both current baluns that act for choking common mode currents and > transform a balanced load to an unbalanced load. If you place a common > mode choke at the antenna feed point, the system will be unbalanced, > usually. > > Next, most tuners that have built in baluns use voltage type baluns > and can be less than good in a high SWR situation. However, using a good > current balun at or neat the tuner usually prevents common mode issues. > However nothing is 100% when dealing with RF. > > Putting reactance in the line to counter what is already there is > good when dealing with the impedance, but you are correct about > complexity. The very simplest configuration that I know in a multiband > situation is to erect a dipole for the lowest frequency to be used and > feeding it with ladder line, or equal. Where you enter the house mount a > 4:1 current balun and connect coax from there to the tuner. As long as > your tuner can handle the SWR and the coax run is short, you need not > worry about losses due to SWR; I am speaking to the 1 or so db losses > over just the transmission line loss. If you use the tuner in your > Elecraft gear, I just wouldn't worry, period. Elecraft tuners appear to > be able to handle anything I've put in my backyard so far. > > The Johnson matchbox line of tuners were excellent. I no longer have > mine; selling mine was a less than brilliant move on my part, in > retrospect. However, I don't usually recommend this approach. Getting > through some of the walls/windows in the houses around here with > balanced line can be problematic. So, I usually recommend the approach > above for overall simplicity and assurance of maintaining feed balance. > > 73, > Barry > K3NDM > > ------ Original Message ------ > From: "Vic Rosenthal" <[email protected]> > To: "Al Lorona" <[email protected]> > Cc: [email protected] > Sent: 1/14/2019 1:12:37 AM > Subject: Re: [Elecraft] Slightly Unbalanced dipole? > > >Why would a common mode choke at the antenna feedpoint present more > problems than the common practice of feeding a balanced line through a > single-ended tuner and balun? > >I’ve done a lot of experimenting with the latter and have learned that a) > the best configuration is with a 1:1 balun, and b) the balun will become > lossy and heat up if the impedance it sees is highly reactive. The solution > to b) is to cancel the reactance by putting the appropriate opposite > reactance in both sides of the line between the balun and the antenna. Of > course this means added complexity. > >I would love to figure out how to make a choke that would work with > balanced line at the antenna feedpoint, on multiple bands without any > additional components. > >FWIW I’ve switched to a real balanced tuner (Johnson Matchbox). > > > >Victor 4X6GP > > > >> On 14 Jan 2019, at 1:42, Al Lorona <[email protected]> wrote: > >> > >> By the way, whenever Jim says, "...a very good common mode choke at > the feedpoint of an antenna...," he means an antenna fed with coax. For the > rest of us, of course, that choke would (should) go at the output of the > antenna tuner, whether in the shack or close by. > >> > >> Al W6LX > >> > >> > >> ______________________________________________________________ > >> 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] > >______________________________________________________________ > >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] > > ______________________________________________________________ > 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] -- -+-+-+-+- Jenny Everywhere's Infinite: Quark Time http://quarktime.net ______________________________________________________________ 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]
