Home 8circle 40m verticals

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8ele vertical circle array - The introduction
Written by Administrator   
Thursday, 01 July 2010 18:58

Beginning in 2009, I spent lots of time to build up my new antenna for my home qth in jo10os. I took me the last years summer to put all the radials in the garden - I will document the set-up in detail here on my website>
See you on 40m - at the moment testing, but still some work to be done...

 

How to compete on 40m without having a tower?


While I found at my contest station, that you can compete with a good vertical array, if you have excellent ground conditions, I was not sure, whether verticals would be effective at my home qth. Here at home (jo10os), 60km south of my contest place (jo11of), I don't have the elevated steel roof of 2000m2 and no saltwater. It is almost a flat area, with relatively good takeoff in most directions, but the ground conditions for verticals seemed to me questionable. Also I have lots of trees ant plants in the garden, so I didn't know, how a vertical array will behave in between a garden with so many trees...
Although many questions arose, I decided to give it a try with building the ultimate vertical array - a full-size 8-circle array for 40m. I started with the antenna building begin of August 2009, during summer holiday - the following steps had to be taken:
- decide the best position within the garden for the verticals
- place wodden poles to fix the verticals
- roll-out of the radial system
- building of the vertical elements
- building of the vertical fixation mechanics
- pre-testing the first vertical against my low inv-V dipole
- cutting 3/4 wavelength 75 Ohm coax cable for exact electrical length
- set-up of all 8 verticals and tuning to resonance
- tuning of element currents and phasing
- testing and first experience
- audio files

Last Updated on Tuesday, 03 August 2010 13:09
 
What can I expect from the 8circle array
Written by Administrator   
Tuesday, 03 August 2010 10:50

What is the best configuration of verticals in my garden ?

In order to compete on 40m, it is necessary for a transmit antenna to aim for maximum gain. While a 3 ele Yagi can reach about +13dbi of gain over flat terrain at very interesting elevations for DX and EU communication, I wanted an array which should not be too far away from that performance. After a lot of calculation, I came up with the following data:

Circle diameter: 28,68m
End-fire spacing: 10.98m
End-fire phasing: 120 degrees
Broadside spacing: 0.627 wavelength = 26.50m
Broadside phasing: 0 degrees (=in phase)

The positioning of the verticals looks like this: (please click on the images for a larger view)
The positioning of elements for 8ele circle array at ON5KQ. The distance between Ant 1 and 3 is 26.5m. The distance between 1 and 2 is 10.9m
For one particular antenna direction only 4 elements are used. All other elements are floating, which means there should be a high impedance at the feed-point of all un-used elements to be electrically invisible. So if I want to radiate in direction of the x-axis, I will use antenna 1, 2, 3 and 4 - all other elements floating. Antenna 1 and 2 forms a 2 ele end-fire vertical beam with end-fire spacing. Antenna 1 and 3 is a broadside cell of 2 elements with broadside spacing. Antenna 1 and Antenna 3 are phased against Antenna 2 and Antenna 4 with the end-fire phasing of 120degrees. Antenna 1 and 3 are in phase and Antenna 2 and 4 are in phase with broadside phasing of 0 degrees.

Fortunately this situation matches very well with the local circumstances and space available. Most of the verticals are relatively near to the edges of my own property. I can permanently install radials all around the antenna using my own property.
However some of the antennas are very close to trees (2-3m only). These trees are about 13-14m high - I wonder whether it will be a difference in winter, when there are no leaves... we will see...


The patterns of this vertical array looks like this: (please click on the images for a larger view)

  Vertical elevation pattern of 8circle vertical array over very good ground compared with 2ele full-size 40m Yagi at 22m height (boomlength 7.15m)  Horizontal azimut pattern of 8circle vertical array at ON5KQ at 22 degrees. For comparison in blue the horizontal pattern of a 2ele full-size Yagi at 22m height for its maximum radiation at slightly higher elevation angle of 26degrees

For comparison I put the patterns of a fullsize 2ele Yagi on a 22m high tower over flat terrein in blue (boomlength of 7.15m)

Conclusion:

It is hard to compete on gain with the 8 circle array against a very large full-size 2ele Yagi on a tower of at least 20m high.
In the optimum case the yagi will be most likely a little louder, if the yagi is over very flat terrein without obstacles (flat fields, etc. in a typical rural QTH)

Advantages of my new 8circle 40m full-size vertical array:

- Once the ground system is installed for the verticals, the vertical system is much easier to maintain, than a large full-size 40 Yagi
- switching directions is instantly done with the verticals - the Yagi would need time to rotate
- the azimut pattern shows, that the 8circle has a much narrower horizontal lobe, than the Yagi - that can help in crowdy European band conditions to knock-down QRM from the side of the antenna much better, than possible with a Yagi
- high angle elevations are better supressed with the Vertical than with the Yagi, especially if the Yagi is not high enough in the tower - the verticals will always beat the Yagi, if the Yagi is below 20m in height
 

Last Updated on Friday, 13 August 2010 13:04
 


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