Are you looking for a near Omni for horizontal on VHF, have a read here:
http://www.qsl.net/dk7zb/zigzag/zz-Englisch.html
It has plenty of promise for beacon antenna but have to work out how to make a 9:1 BALUN for 144 and above..
Any BALUN ideas for VHF / UHF ?
Peter, vk5pj
Peter
Did you also check out the construction article at
http://www.qsl.net/dk7zb/zigzag/zz-construction.htm
Not quite sure where you got "9:1" from as it looks to be a standard 4:1 half wave coax balun arrangement in the article, unless you add all of the extra sections (eg 10 el) to cause the feed impedance to rise.
Hi Doug,
I am a HAM of course I want the 10 element version :
as it gives me more gain
Peter
Well in truth, the 10 element version allows me to feed from the most lower part of the zig-zag and also gives a pretty good 'near omni' pattern which is what I want for our beacons on 144 & 432...
It should not be overly complex to build and could be hung from an outrigger on a tower, a pretty appealing set of characteristics so far..
Peter
Hi all, I wouldn't go there. Period.
Looking at the 8el azimuth pattern, a 9db dip is not acceptable.
There was NO mention of the Vertical component of the radiation.
The 9:1 balun, that's the easiest thing at a fixed frequency.
Two pieces of 9mm copper pipe 1/4 wave long....
Saw a hole in one 1/3 the way up etc...
Maybe brass angle would be easier: >< coax in the groove one side.
Lastly, the vertical spacing of the dipoles should be 0.65 wave for best gain.
The need for a non-conductive support mast also precludes running a coax
up and putting another antenna on top of it eg. 23cm.
Too hard
The ZigZag antenna is in effect an end fed antenna, in other words a co-linear antenna.
In co-linear antennas the phasing between elements is somewhat important as it determines where the angle of the maximum beam radiation. Thus as the frequency changes so does the beam tilt. Getting this right for the frequency you want may be difficult. This difficulty increases with more elements in the antenna the as beam becomes narrower. Unfortunately the beam cannot be seen and certainly does not show up in VSWR readings. Adjusting the VSWR as suggested in the ZigZag antenna article by altering the length of the end element finishes up playing with the beam tilt. There is no point in having a good VSWR with gain in a direction that is of no use.
Feeding each radiating dipole in parallel ensures that all the dipoles are fed in the same phase and overcomes the beam tilting as the frequency changes. If beam tilt is required with this feed arrangement this is achieved by varying the length of the feeder cables to achieve the desired fed phase difference between the dipoles.
Unfortunately achievable the theoretical antenna gain and pattern can be quite somewhat elusive! I am still looking for an easy solution.
To date I still have not found the ideal antenna, but I am still looking.
PS: Beam skewing is fine. TV stations use it. However it needs to go where it is needed!
Gents,
Although strictly not the same as the discussion above, the following article gives a good insight into the issue of end feeding antennas and the importance of keeping the phasing within close tolerances.
http://k5rmg.com/old-web/Pages/Tech%20Ar...0QEX-1.pdf
The end result provides excellent omnidirectional HORIZONTAL polarisation with good gain and can be extrapolated down in frequency and down in number of turns, as discussed at the end of the article.
Definitely a good read and food for thought for beacon operators.
Cheers
Peter VK3QI