[TowerTalk] 8circle vertical array for transmit - ON5KQ

[on5kq at on5kq.be]

Dear,
this is to mention, that I am using my 8 circle vertical array for 3 years now on
40m. I realize, that several station mainly using the 8 ele circle vertical array
for reception especially for 160m as an alternative to large beverage arrays.

I first heard about this 8circle transit array many years ago, when Tom, W8JI
mentioned it on his website. 3 years ago I was able to put a TX version for 40m
in my own garden - with incredible results!

You can see a picture of the array on QRZ.com - scroll down to the panoramic
photo in the text...

some remarks:
- for transmit you need resonant elements with resonance frequency being exactly
the same
- you need very good ground and should use as many radials as possible (I have
used 8km of wire for buried radials to keep losses as low as possible)
- for large phased arrays, I don't like elevated radials, because it will be very
difficult to maintain symmetry of phase shift and magnitude of the elements, when
switching directions
- due to the resonant elements mutual coupling is very prononced and you should
take care of that as with every transmit phased array
- configuration is as such, that always 4ele are working as a boradside endfire
array and 4 elements are not working. Not-working means, that these elements
should not carry any element current and therefore should not couple at all with
the elements in use. The only way to achieve this, is to take the unused elements
out of resonance. I introduce high impedance to the feedpoints of the unused
elements by shorting the 3/4wave feedlines of the unused elements. This works
very well for me.
Note: This issue is unfortunately not mentioned in ON4UN book. The relay
schematic in ON4UN's book for a transmit array therefore will not work, because
the unused elements will couple heavily with the unsed elements and will in
practice detroy the pattern completely !
- I adjust the array for having 115-120 degrees endfire phase shift with same
magnitude. Broadside phase shift should be in phase of coarse (0 degree phase shift)
- spacing of the elements is about 10.5m enfire and 26,5m broadside (see my
website: www.on5kq.be)
- adjustment is done by probing the voltages at the beginning of the 3/4wave
75Ohm feedlines with a 4stroke scope
- adjustment of element resonance and impedances as  well as measurement of the
electrical length of 75Ohm coax has been done with N2PK network analyser

Results:
Signal strength on transmit is at similar to full-size 2ele Yagi on 25m tower
Reception is much better due to the very narrow pattern and RDA of roughly 13dB
Rx performance is at least same than my previous beverages covering 28ha of land
- so I don't use them at all on 40m any more
Performance is very good in contests because of very quick switching and very
narrow lobes. I don't find any disadvantage to the narrow lobes...

F/B is at least 25db - but could be much more accoasionally. Front to side is
about 30db difference, as many tests have documented...

If anyone wants more info - please see my website: www.on5kq.be of drop me an
e-mail (adres is ok on qrz.com)

talk to you on 40m,

regards, Ulli
on5kq