Tuning the sloper

Last Updated on Wednesday, August 31, 2011 7:38 PM Written by N1WQ Wednesday, August 31, 2011 7:30 PM

Last weekend I spent several hours trying to tune up my antenna for lower bands, Alpha-Delta DX-B quarter wave sloper. It is a quite narrow range antenna, and initially I did not have time to tune it for all bands, so I ended up with DX portion of 160M band (around 1,83MHz), and some rarely used part of 80M band, around 3,65MHz. On 40M the resonant frequency was around 8MHz with some insane VSWR inside amateur band. The 30M was not a problem at all though.

Well, the result is a bit disappointing. First of all, I figured out I cannot tune the sloper on 40M, it needs to be extended too much for that, so VSWR on this band is between 3 and 4 now, with resonant point at around 7,6MHz.

Then I discovered, that resonant frequencies of this antenna on 80M and 160M seem to be harmonics, so I cannot tune it for both DX part of 160M band and CW part of 80M band at the same time. I gave preference to CW portion of 80M, because I need new DXCC countries on this band for 5B-DXCC. However to achieve this result I used small vertical part of the wire almost at the end of the antenna, as shown on the picture below. So if I need resonance point back on 1,83MHz, all I have to do is to tie this “tail” back to main wire. This trick might theoretically affect antenna effectiveness, but I doubt it. The quarter wave slope is actually three-pole antenna, which also includes the tower and the beam above it, and the tower and the grounding below. I do not believe this small vertical piece of wire can ruin such a complicated and unpredictable configuration.

DX-B, the tuning wire, Aug 2011

 
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