Topband: 2 element vertical for 80m with 1/8wavelength spacing

[John Kaufmann]

I also use a vertical phased array with 1/8-wave spacing on 80m.  I did this because of limited space.  Like PE5T describes in his post below, I used the method in ON4UN's book and originally described in a series of articles by K2BT in Ham Radio magazine (no longer in publication) in the 1980's.  I designed my own custom L-C circuits for phasing and matching.  I don't think there is a simple plug-and-play solution that would provide good performance at close spacing like this.

As Kees says, the impedances at close spacing are low and you have to work at keeping losses small.  Otherwise you don't realize the theoretical gain.  This means a large radial system.  I use over 100 radials per element.   The theoretical gain of my system is about 4 dB.  This is about what I see in practice comparing my 2-element array to a single reference vertical.  My array is optimized for the low end of the 80m CW band and I get up to 25 dB F/B.  I still see some F/B as high as 3700 kHz but by 3800 kHz it is omnidirectional.  The SWR is close to 1:1 at 3500 kHz but goes up to 2:1 around 3550 kHz.

I use a separate network optimized for 3800 kHz for SSB, but 98% of my operation is CW.

The system does work very well provided you have a good ground system.  I have worked 333 countries on 80m with this system from an average suburban location.

I also retune this system for 160m operation, but that is another story.

73, John W1FV

-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of Kees Nijdam
Sent: Tuesday, April 19, 2016 12:07 PM
To: Filipe Lopes; topband
Subject: Re: Topband: 2 element vertical for 80m with 1/8wavelength spacing

Hello Filipe,

Yes, I have such a system.
Cost me several days to optimize it.
My comments.
The 2x157 and 39 degrees phasing lines are based on very good earth systems
(2-3 Ohm). When your radial network is 5 Ohms, it is a different story. That is because the driving impedances are very low (in my case 19,27+j21,14 Ohms and 13,86-j15,73 Ohms) and the influence of the earth system on these impedances is big (a 1/4 lambda system is not that critical) If you do not know the impedances of your verticals, the only way to go forward is to measure the self impedances and the coupled impedances. After that you can follow the calc ulations in ON4UN's book and software.

My system is optimized for 3510 kHz and with a signal source at 400 meters I found a front to back ratio of 24 dB for this frequency.
On 3500/3520 kHz is was  20 dB, on 3540 kHz only 10 dB and higher in frequency  the antenna becomes more and more omni directional.
However, the swr was OK over the whole band, also on 3800 kHz.
So it can be used on 3800 kHz but without directivity.

You need a very good radial system and to decide for CW or SSB . My advice: 
better and less critical is to increase the distance between the verticals with a few meters.

Is it worth the effort? Yes I think so. I have one vertical permanent and during the winter I install the other. The few dB extra gain is good but I was also very happy with the system as RX antenna. I have it oriented north-south and it is nice to hear KH6AT over the south pole and not over the north pole..

Kees, PE5T