Alpha-Delta DX-LB Tuning Issue

[KA2PFL]

Having an issue with a newly installed Alpha-Delta DX-LB. This replaced a sloper antenna on my tower mounted 55 feet up.



The lowest SWR below was measured on each band with a rig expert antenna analyzer and verified with my HF radio.



40 Meters 6.565 MHz would like to tune it for FT-8 at 7.074 appears antenna is too long.



80 Meters 3.856 MHz would like to tune it for FT-8 at 3.573 appears antenna is too short.



160 Meters 1.827 MHz would like to tune it for FT-8 at 1.840 appears antenna is too long.



Was going to start by shortening up the 40 Meter wire first. Then lengthen the wire between the 80 Meter loading coil and the 160 Meter coil. Then finally fold back (shorten) the wire from the bottom of the 160 Meter coil.



Is this the best way to go about tuning this antenna? Is there some way to calculate how much to cut and or lengthen the wire for each band section?



Thanks,

Louie KA2PFL

 

[K6GBW]

Final tuning will always depend on how it’s deployed, so being slight off is to ne expected. The Alpha antennas should come with plenty of wire to make those adjustments. Since the adjustments depend on a lot of factors (height, things around it) you can’t really use the meter to get an exact formula. So just do it in small amounts. On 40 meters you can probably shorten it by about 4-5 inches on each side and not overshoot your goal. It’s a pain raising and lowering it that much, but it’s pretty much the only way to do it. If you get it remotely close it will tune up easily with a rigs internal tuner and you won’t suffer any noticeable loss. Just try to get it under 3 and use the tuner. At 55 feet you'll have a great antenna! Most of us can't get ours anywhere near that high.

 

[K6GBW]

When I re-read your post, I realized I didn't actually answer your question. When I saw Alpha Delta, my mind went right to their fan dipoles, but you are talking the DX-LB model. So first off, you aren't going to get a really good SWR across all those bands. The band width of 160-80-40 is just too wide for that, so you will end up using a tuner regardless. But the correct way to tune these is to tune them inside out. Start with 40 meters, then 80 and finally 160. Pick the frequency in each band where you work the most and that's your target. Once you get the SWR down to a reasonable level at the target frequency then stop. This is made harder because you have the antenna up fairly high and you'll have to take it down to tune it. The measurement down low will change as you put it back up (likely needing a longer length). If it tunes using a tuner now I'd leave it alone. The slight loss from the tuner isn't really going to be noticeable. A DX-LB at 55 feet is going to be a good antenna, so I expect you're going to get out very very well.

 

[KA2PFL]

Thanks for your advice. Currently setting up an antenna tuner as you suggested.