Home > Daily News, HF, Home Brew > Fine Tuning the 32.3 ft Vertical- A better Antenna for 15m

Fine Tuning the 32.3 ft Vertical- A better Antenna for 15m

So my last post, described a better 15m vertical, which I had some success with. It tuned up where I wanted it to, but I had not had the chance to check it with the MFJ259B analyser. Though intended for 15 meters, where it is a 3/4 wavelength,  it is designed to be resonant at the lower part of the 40m band, where it would be a 1/4 wave. I finally got the opportunity to test it and I found it resonant at 6.8 MHz rather than at 7.000 – 7.010 as planned. I checked it at 21 MHz and found it resonant at a lower frequency- not what I wanted. I fiddled with the antenna length but just got nowhere. I then thought maybe the long 2 metre aluminium section of the base of the vertical which was now part of the radial system was somehow changing the resonance. So I lowered the assembly so that the feed point and radials were closer together and restablished the calculated vertical element length (after trimming it previously).

Before

Scan 1

With this lowered feed point, I was finally able to get the antenna resonant approximately where I wanted it to be. The results are below.

Freq MHz   R              X          SWR

7.000         31              0           1.2:1

7.300          32             0           1.2:1

21.000       125            0           1.5:1

21.340       133            0            1.6:1

And just for good measure

18.068      42             16           2.2:1

18.150       51              19           2.2:1

24.890      23              0            1.9:1

24.950      25               0            1.9:1

28.000      166            0            1.9:1

29.300      21               0            1.9:1

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Categories: Daily News, HF, Home Brew
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