Don... Many hams - as I have done/do - use coax to get out of the house, connect it to a balun, and then connect twinlead from the balun to an antenna. There is a lot of commentary on this setup, but perhaps another time through would be helpful. The questions arise: - if the coax is short, say under ten feet, is this setup more or less equivalent to running the twinlead all the way from the antenna to the transmitter? - again, if the coax is short, will RG8 or 213 be sufficient to the task? - is there any advantage of one balun ratio to another [1:1, 4:1, 9:1]?
Happy New Year, and thanks for your contributions here on the Elecraft reflector. ...robert On 12/31/2011 17:42, Don Wilhelm wrote: > George, > > Short question, long answer follows -- > > Do to constraints at home, I no longer use open wire or ladder line > feeders, but when I did use them, I found several things were true if > you did not want them to radiate (and create RF in the Shack). > My first rule is to use balanced antennas - off center fed antennas are > famous for feedline radiation and RF in the shack. > The second rule is to run the feedline away from the antenna at right > angles for as great a length as you can manage, but certainly for a > quarterwavelength - The feedline can pick up radiation from the antenna > if this rule is not followed. > Third is to run the feedline correctly - use nice gentle bends if you > must change direction, support it using as few hangers as possible (if > you can put the feedline under tension, you can get away with very few > supports) but support it so it is stable even in the wind. Do not run > it parallel to other conductors, but you may cross a conductor at right > angles if necessary. The line should be spaced away from other objects > by at least 3 times the spacing of the conductors. > > Lastly, If I could, use a true balanced tuner, link coupled is best, so > if you see a Johnson Matchbox at a hamfest, get it. If you must use an > unbalanced tuner, use a good balun at the output (see K9AY's info on > baluns). BTW, do not assume that a 4:1 balun is the thing to use, the > feedpoint impedance in the shack can vary wildly from very low to very high. > > If you do encounter a high impedance feedpoint on any band, that will > place a high RF voltage point at the shack end - add or subtract some > feedline to bring the feedpoint impedance down. > If you do not understand how the feedpoint impedance changes with the > length, take a look at the Antenna article on my website www.w3fpr.com > > 73, > Don W3FPR > > On 12/31/2011 11:25 AM, [email protected] wrote: >> Those of you using open wire feed lines. How do you keep RF out of the >> shack? 73 George/W2BPI K2/100 >> > ______________________________________________________________ > 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
