Wednesday, 15 August 2012

The 31' Homebrew Vertical

Several people have asked me to post the results of our field test of the homebrew 31' vertical antenna.  Here it is:

Background –

At Chilicon 2011 some of the members of the Ottawa QRP Society arrived with a homebrew vertical antenna. It had a 28’ radiator, one 16’ ground radial, one 31’ ground radial, and a 4:1 Balun, all designed by Martin-VA3SIE. It intrigued VE3CLQ with its simplicity, and its possibility as a ground-wave antenna for emcomm work.

VE3CLQ built one at Chilicon 2011 using a MFJ-1910 collapsible mast, a 28’ radiator, four 16’ ground radials, and a 4:1 Balun. This antenna was not analyzed before use, but with 40w output from a FT-857D it worked VK3MO in Victoria, Australia and VK2KRR in New South Wales, Australia from his campsite.

Further Development –

Richard-VA3VDP played with the design using the EZNEC antenna design computer program for a few weeks and came up with the result that a 31’ radiator would work best with the 16’ ground radials. A rebuild of VE3CLQ’s antenna ensued and it was soon sporting a 31’ radiator, this antenna is now known as the Chilicon Vertical Mk.2.

VA3VDP bought the commercial version of this antenna, made by LDG, and called the S9v31 and is advertised to be good for 6m through 40m.

Over the past 12 months the antenna has been used, both the commercial and the homebrew versions, with good success from a variety of locations and grounds. A great deal of DX has been worked to date with it.

The only change to the Chilicon Vertical Mk.2 has been with the number of and the length to the ground radial system. 

Testing –

In order to find out which Balun, either a 4:1 or a 1:1 was more efficient, a test was designed. The antenna was set up at Lamoine Point, in a gravel parking lot.

The antenna was set up with the 31’ radiator, six 16’ground radials, and a 4:1 Balun. Frequencies where chosen close to the centre of each band for operating SSB. With exactly the same set-up we switched to a 1:1 Balun and the same test run again. The results were:

The 4:1 Balun
Frequency        Result
3.800                6.5:1
7.150                3.5:1
14.150              2.5:1   
21.200              1.8:1   
28.500              2.1:1   
53.0                  1.1:1       

The 1:1 Balun
Frequency         Result
3.800                12.1:1
7.150                2.6:1
14.150              6.3:1
21.200              1.6:1
28.500              4.5:1
53.0                  1.3:1

The antenna was set up for a second test with the 31’ radiator, six 16’ground radials, a 4:1 Balun and the addition of two 31' ground radials. Frequencies where chosen close to the centre of each band for operating SSB. With exactly the same set-up we switched to a 1:1 Balun and the same test run again. The results were:

The 4:1 Balun
Frequency           Result
3.800                  6.1:1        
7.150                  3.1:1        
14.150                2.4:1        
21.200                2.1:1        
28.500                2.1:1        
53.0                    1.1:1        

The 1:1 Balun

Frequency          Result

3.800                 12.1:1
7.150                 2.8:1
14.150               6.3:1
21.200               2.4:1
28.500               1.3:1
53.0                   1.4:1

The results show that the addition of the two 31’ ground radials did very little to change the feedpoint impedance of the antenna.

We then checked the resonance of the antenna using both a 4:1 Balun and then the 1:1 Balun. The results are:

The 4:1 Balun
Frequency          Result

9.500 MHz        1.0:1
19.700 MHz      1.0:1
42.600 MHz      1.0:1
61.900 MHz      1.0:1
132.000 MHz    1.0:1

The 1:1 Balun
Frequency           Result

7.500 MHz         1.0:1
35.000 MHz       1.3:1
64.500 MHz       1.1:1

On Air Test -

The antenna was quickly reconfigured to the 31’ radiator, six 16’ground radials, two 31’ ground radials and a 4:1 Balun. The antenna was then connected to an IC-703 10w QRP transceiver and a 12v 35Ah gel cell battery.

The results of the on air test are:

1901UTC    20m   G8A           57/55    Brian, Great Sutton, UK
1907 UTC   20m   VY2TT      58/56    Ken, Bloomfield Stn, PEI
1921 UTC   15m   CM8AKD  57/56    Jose, Las Tunas, Cuba

The SFI for that time was:

SFI = 129;  A index = 5;  K index = 3; and SN = 91.

Conclusion –

In its present configuration as the Chilicon Vertical Mk.2 it works very well and is especially good when hunting DX.

Further testing is scheduled to be done with more radials of different lengths.  If there is suffient interest I'll post the results.

1 comment:

  1. Bill....

    I totally agree with your findings... I cloned the S9 31 foot vertical using a 4:1 balun and the mfj masting. I ran out as many radials at various lengths as was practical for the operation and had exceptional results.

    As you know I use the 43 foot version at home and have had decent results (135 DXCC) in the one year I have used it....

    The 31 foot version has been a strong transportable station contender with the stronger battery and my FT 897