HI Don, I wish to look into the TLW application you mention. However, I am not what it is exactly. Would you please be so kind as to point me in the proper direction.
I most likely will be going back to the 1:1 balun but the promise of swr of 1.3 on 160m was nice, which I have on the 4:1. Also it is a current balun. Thanks ~73 Don KD8NNU On Wed, Jan 11, 2012 at 5:02 PM, Don Wilhelm wrote: > Don, > > According to L B Cebik's modeling, a 2 wavelength horizontal loop will > have a feedpoint impedance of 180 - j125 ohms, and a 4 wavelength loop > (the same loop used on 80 meters will have a feedpoint impedance of > 235 - j135. > Both are good candidates for the use of a 4:1 balun - but that only > applies if you mount the balun right at the antenna feedpoint. The > fact that you have 60 feet of 450 ohm feedline changes the situation > drastically - that is about 1/8 wavelength on 160 and close to 1/4 > wavelength on 80 - so the feedoint impedance at the end of that 60 > feet of feedline is quite a bit lower - that is most likely why your > 1:1 balun worked so well. You can work with L B Cebik's antenna > feedpoint impedances and the TLW application available from the ARRL > to find the feedpoint impedance at the end of the 60 foot feedline, > but I think you will find it closer to 50 ohms than to 200 ohms. > > The other question is what type of balun is your 4:1 balun - if it is > a voltage type, it has no chance of stopping common mode current. > > My guess for why your current choke did not work is either that you > did not place it at the right point on the coax, or it was at a point > where the RF voltage was high, and in light of a high RF voltage > (think impedance equal to 2000 to 4000 ohms, a choke of 5000 ohms > impedance does not have much of a chance to stop any current. > > So bottom line - go back to what you had before, or put the 4:1 balun > at the antenna feedpoint where it should work if your antenna is > anything like L B Cebik's simulations. > > 73, > Don W3FPR > > On 1/11/2012 4:12 PM, [email protected] wrote: >> 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. >> >> ______________________________________________________________ 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
