1960's 80 meter dipole

[N4JKD]

I recently acquired something you don't see very much of anymore. I was given an 80 meter dipole that was built by the U.S. military, to be used as part of a large portable wire array, which had wires for 160-10, plus several other frequencies. I was told the array was originally around 200 feet tall, and had two antenna towers on both sides. It is my current setup, at about 35 feet in the air, and fed with a 1:1 balun made by The Wireman, and currently fed with RG8. I have a plan in the works to run 450 ohm ladder line to the inside, and couple it with a short run of coax, since my antenna tuner does not accept ladder line. This would make it a classic doublet, but it works well with coax, and haven't fully decided if I want to do this yet. That, and my tuner does not accept ladder line, so I would have to make a junction for ladder line to SO-239 to run a very short run of coax. I already have the balun, but I am concerned about impedance issues It is already resonant on all bands from 80-10 meters.

 

[prcguy]

For transitioning ladder line on a 10-80m dipole to coax you want to use a 1:1 ferrite loaded current balun. The reason is you don't know what impedance will be at the end of the ladder line and it could be very low to very high impedance. Using a 1:1 will work fine and better than a 4:1 on a band where the impedance is very low and it will still work fine if the impedance is very high.

All your doing with the 1:1 balun is isolating the balanced line from the unbalanced coax and a good 1:1 current balun should achieve about 20-30dB of isolation depending on frequency. You also want to use super low loss coax even if its a short run because the VSWR on the coax will be really bad at some frequencies and coax loss goes way up when operated under high VSWR conditions.

 

[N4JKD]

For transitioning ladder line on a 10-80m dipole to coax you want to use a 1:1 ferrite loaded current balun. The reason is you don't know what impedance will be at the end of the ladder line and it could be very low to very high impedance. Using a 1:1 will work fine and better than a 4:1 on a band where the impedance is very low and it will still work fine if the impedance is very high.

All your doing with the 1:1 balun is isolating the balanced line from the unbalanced coax and a good 1:1 current balun should achieve about 20-30dB of isolation depending on frequency. You also want to use super low loss coax even if its a short run because the VSWR on the coax will be really bad at some frequencies and coax loss goes way up when operated under high VSWR conditions.

Currently I only have a 40 ft section of RG8 and I have read that using that, I don't need to coil it. I only need maybe a 10 ft section of RG8 or better to connect from the balun to the radio. I tried the other night, and the best I could get on 80 meters was a 9:1 SWR, and I figure that is the mismatch at the coax. I wish this tuner had an option to run ladder line directly in, because I would be in business.