Jim... Thanks for your reply. I think I've been unclear in my question. I'm not concerned as to what "it" is called, how to build "it" or what "it" costs. These things can all be agreed upon and implemented.
What I'm curious about is whether some such device, at the feed point of a doublet, in turn fed by window line is of any use [assuming an appropriate tuner at the radio end of the line]. You have said, accurately so, that a current choke at the feed point of a dipole [let's leave off-center fed antennas out of it at this point], in turn fed by coax, keeps RF from flowing on the outside of the coax and subsequently becoming "part of the antenna" and in turn picking up noise/etc. Another way of phrasing my question is, does the coax situation apply to open feeders, also? For example, let's say we have a Johnson Match Box with balanced output, connected to open feeders, running up to a doublet antenna; is there any point in putting some sort of coupling device at the feed point between the line and the antenna? Still another way of asking this is: assuming a real antenna will be unbalanced due to all the usual factors, is there any way, and is there any RF benefit, in forcing a current balance into the open wire feeder? Thanks for your patience and input. ...robert On 9/29/2012 21:43, Jim Brown wrote: > On 9/29/2012 11:26 AM, Robert G. Strickland wrote: >> Is there anything to be gained in putting a 1:1 "balanced isolator" at the >> feed point >> of an antenna that is fed by a "parallel wire" feed line? Does such an >> arrangement >> achieve feed line isolation while preserving the ability of such an antenna >> to be >> driven on various bands other than its resonant frequency? Thanks for your >> input. > > Phrases and words like "balanced isolator" and "balun" are not only > confusing, they are used to separate people from their money. The > chokes described in my RFI tutorial can be built for the price of a > single #31 core, a few yards of THHN wire, and a couple of connectors. > You can put it in a box if you like, but it's only cosmetic. These > chokes will handle legal power IF the antennas are not badly > unbalanced. Off-center feed creates massive imbalance, and will fry > even the best of chokes. The relatively small imbalances created by > surrounding objects will not -- they simply couple noise. > > #31 cores cost about $4.50 in 1,000 lots, about $7 if you buy 100, and > $15 from the rip-off vendors who advertise in QST. It's become fairly > common for ham clubs to get together and make a group purchase. Over a > period of about 8 years, I've been part of several at the 1,000-piece > level. There are guidelines in Appendix One of the tutorial about how > and where to buy. It's worth buying in quantity, because these 2.4-in > diameter cores are almost universally useful for RFI suppression. > > 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 > -- Robert G. Strickland, PhD, ABPH - KE2WY [email protected] Syracuse, New York, USA ______________________________________________________________ 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
