Don: You have standing waves on the coax. That means that there will be varying levels of RF voltage on the coax that change with frequency and that are not prevented by a balun at the transition from coax to open wire line. The 4:1 balun has altered the load impedance and changed the voltage a the shack.
You said the original arrangement worked fine. Why not go back to it? Personally, I'd take all the baluns out and see if I had any "RF in the Shack" issues. Any "passive" device like a balun eats RF. Sometimes it's not enough to care about - sometimes it's a LOT. So I try to keep my installations a simple as possible. Also, every foot of coax (or any other transmission line) eats RF. How much depends upon the impedance of the line, whether it's connected to a load with the same impedance, and the frequency of operation. Coax is generally the worst type of line to use in an unmatched system with standing waves due to its rather low impedance, so keep it as short as possible. 73, Ron AC7AC -----Original Message----- Gents, I have a ladder line and balun question that I hope someone can guide me thru. I had a good working antenna system with two antennas. First being an Alpha Delta Dipole and the second a 2WL 160m loop antenna at 40 ft in the air strung in trees. So the wire does touch the trees. Dipole is fed with coax and choked at the feed point and the loop was fed with 60 ft of ladder line to a 1:1 current balun then 25ft coax to the shack tuner. Then the amp and radio. This combination was working real well no RF problems in the shack. I was advised that I would obtain better results for better SWR at resonance and easier matching if I removed the 1:1 balun and went to a 4:1 balun. I made this change with everything else being the same. I now had RF in the shack again. I then added an isolation balun to the system by adding 6ft coax from the output of the 4:1 to a balun designs 116du which is supposed to have 4500 ohms of choking impedance on 160m and over 5000 ohms choking impedance on 80 and 40 meters. This did not eliminate the RF and I am still having problems. So here is the question, is it possible that with the combination of length of the ladder line at 60ft plus the 6 ft plus 25 ft of coax I am at a feed line length that will be a problem no matter what I do. I keep looking at the internet to try and figure this out but I am confused as some information I find says it only applies to 1:1 baluns or other factors. So anyone who can help me understand this feed line question I will be greatly appreciative. Thanks Don ~73 Don KD8NNU ______________________________________________________________ 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
