Home > Daily News, HF, Home Brew > Analysis of ZS6BKW Antenna

Analysis of ZS6BKW Antenna

I finally received my MFJ  antenna analyser and set to work immediately checking some of my antennas. The first one I checked is the only one left standing after Cyclone Yasi. I refer to it as ZS6BKW No2, as it is the second of the two homebrew ZS6BKW antennas I built.

It is one of those interesting things that happen. I have always had a tuner in line with this antenna, and from the moment I first used it, I adjusted the tuner setting for each band, never once attempting to use the antenna with the tuner bypassed. After analysis, I found I could use it on most bands without a tuner!

Below are the results. The analyser was connected to coax termination in the shack, hence the result is a product of coax, balun, open wire feedline and dipole.

RESONANT FREQUENCY is where reactance is zero ohms. Since resistance has nothing to do with resonance, the resonant frequency is NOT always at the point of lowest indicated SWR (although they certainly can be the same). The most desirable load is almost always the load with lowest SWR, even though it may not necessarily be the point of no reactance.

Analysis of ZS6BKW Antenna No. 2

kHz R X SWR Comment
3449 32 0 1.5 Resonant frequency. X=0
3500 32 4 1.5 Band Edge. Excellent
3700 36 15 1.6 Band Edge
3600 34 9 1.5 Excellent
6777 39 0 1.2 Resonant frequency. X=0
7115 45 10 1.2 A favorite frequency. Excellent
7300 49 11 1.2 Band Edge. Excellent
13960 28 0 1.6 Resonant across the band X=0
14005 28 0 1.6 Excellent
14230 28 0 1.6 SSTV
14350 29 0 1.6 Excellent
20102 43 0 1.1 Resonant frequency. X=0
21000 54 18 1.4 Band edge. Excellent
21450 40 19 1.6 Band Edge. Excellent
28830 40 0 1.1 Resonant frequency. X=0
28000 48 9 1.2 Band Edge. Excellent
29700 39 0 1.1 Band Edge. Excellent
50256 20 0 2.2 Resonant frequency. X=0 High SWR
52000 82 20 2.1 Band Edge
54000 21 0 2.0 Band Edge moderate/high SWR
143970 27 0 1.7 Resonant frequency. X=0
144000 27 0 1.7 Band edge Excellent
148000 29 0 1.5 Band edge Excellent

I’ll do some more investigation because I am not convinced all is as well as it seems.

Bear in mind I have not examined radiation pattern in this analysis- although I have previously- radiation pattern is just as critical to performance, perhaps more-so in some cases.

Categories: Daily News, HF, Home Brew
  1. June 21, 2012 at 3:07 pm

    From France, sorry for my bad English ! Your results with the ZS6BKW are excellent, and your web site very interesting. In searching on the net, for this antenna there are minor differences according to the different descriptions, it would have been interesting to have some information about YOUR (good !) antenna ( exact length, which twin lead and length, height, shape, balun or no balun …?
    Best 73’s de F1AXE

    • olsenstours
      September 12, 2012 at 11:20 am

      Sorry for late reply. I will let you know exact details, your English is fantastic !

  2. Johnny Pedersen
    October 31, 2012 at 10:29 am

    Hi David
    Do you have any specific details of your setup. I’m surpriced by the flat SWR over such a wide frequency range and the high Resistance on 80meter. According to my modelling the R should be in the range of 6 to 8 ohms in on the 80m band. Seems that you have some high losses somewhere in the chain. How long is the Coax and what type of coax do you use between the antenna and your Tranceiver? I’m planning to build a similar antenna myself. I have all the parts, just need time and weather to set it up. (getting close to winter time here in Norway now 🙂 )

    73 de LA3AKA

    • olsenstours
      October 31, 2012 at 10:43 am

      Yes you are right Johnny. As I commented at the end..I am certain all is not as it seems, and I did mean to update the blog but haven’t done so. The 50 ohm coax purchased locally was rubbish, hence the high losses you mention and that I suspected. I have replaced the coax but have not redone the measurements, but the antenna performs quite a bit better. Having said that, it didn’t perform too badly as it was. Go with the standard measurements and adjust.

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