Running the ladder line horizontally

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AK9R

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Take for example my every day wire antenna, a 94ft flat top dipole at about 35ft fed with a critical length of 450 ohm ladder line (about 40ft) then a 25ft run of LMR-400 to the tuner. This antenna is known as a ZS6BKW and has a very good match on most bands 40m on up but a lousy match on 80m at around 7 to 10:1.
I have a nagging question about this type of antenna and I've never been able to find a definitive answer.

I could put up a ZS6BKW antenna, but I have two related constraints. I would not be able to put the center of the dipole at 35 feet AGL. It would have to be at around 16 feet.

Consequently, my ladder line would have to run vertically down from the center of the dipole to some point close to the ground and then run horizontally for the rest of the 40 feet. Does this matter at all? Or does it matter how close to the ground I'd be running the ladder line? Note that I'd be able to run the horizontal portion of the ladder line perpendicular to the dipole elements in plan view.
 

prcguy

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I have a portable ZS6BKW and G5RV with wire and guy string wound in plastic chalk line reels fed with 300 ohm TV twinlead and have run them close to the ground like the apex at 15ft and the ends a few feet off the ground.

You want to keep the balanced feedline off the ground and I don't have the bottom line distance but I think at least 6" would be a goal. I have seen some degradation in receive with ladder line fed antennas when the majority of the feedline is laid on the ground then it goes back to normal when its lifted slightly off the ground. You can probably find the safe height above ground for balanced line by running it a good 6ft off the ground for its full length, check the match on all bands then lower it until you see some VSWR change. You also want to run the feedline at a right angle from the antenna as far as possible as you mentioned.

I've had long runs of 450 ohm ladder line run across sheet metal roofs using 24" lengths of PVC pipe as vertical supports screwed to cinder blocks as ballast then saw cut the end of the PVC pipe, stick the ladder line in the cut and pound a PVC pipe cap on to keep the ladder line secure in the pipe. I saw no change in VSWR or performance comparing the balanced feedline run at an angle high off off the metal roof compared to 24" horizontally off the same metal roof.

I seen no problem running balanced line from a ZS6BKW horizontally or vertically to the station. On some frequencies the balanced line may radiate a little and when run vertical it may help with low angle takeoff and when run horizontal it may help with NVIS on lower freqs but feedline radiation is or should be a fraction of what the wire elements radiate. You should also use a good 1:1 choke balun at the balanced feedline to coax junction on a G5RV or ZS6BKW to eliminate common mode currents on the coax.

BTW, the ZS6BKW at 15ft with ends a few feet off the ground not only made a great NVIS antenna on 40, 60 and 80m, it also worked coast to coast DX on 40m on up. But so can dipoles laying completely on the ground.
prcguy

I have a nagging question about this type of antenna and I've never been able to find a definitive answer.

I could put up a ZS6BKW antenna, but I have two related constraints. I would not be able to put the center of the dipole at 35 feet AGL. It would have to be at around 16 feet.

Consequently, my ladder line would have to run vertically down from the center of the dipole to some point close to the ground and then run horizontally for the rest of the 40 feet. Does this matter at all? Or does it matter how close to the ground I'd be running the ladder line? Note that I'd be able to run the horizontal portion of the ladder line perpendicular to the dipole elements in plan view.
 

SCPD

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I've run a G5RV jr with the feedline portion horizontal, and worked into Europe with it.
 
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