Topband: Tee Verticals

[Donald Chester]

>What if I short the top hat at the 65' point and at attach just one side of 
>the
>open wire feeder. At this same point I will disconnect the other half of 
>the
>feed line thus creating an approximately 65' vertical radiator (closely 
>resonate
>to 80 meters. At the point of attachment of the elevated radials I can add 
>6 or
>7 additional elevated radials for 80 meters. Keep in mind I will now have 
>an 80
>meter vertical about an inch away from my 160 vertical.

>Do you think that by changing the current configuration I will lose 
>performance
>on either band, will it stay the same, or will it get better?

I say that they are so closely coupled that you might just as well short the 
top and bottom of the oper wire  line, and feed the whole thing as a 
vertical tee on both 80 and 160.  I run open wire feedline up through the 
centre of my 127' tower to feed an 80m dipole at the 119' level.  It is well 
insulated from the tower at all points.  I use the tower itself, which is 
base insulated, as a quarter wave vertical on 160, working against an 
extensive quarter-wave buried radial ground system.

Due to the proximity effect of the dipole and feeder, the base impedance of 
the vertical measures in the HUNDREDS of ohms, instead of approximately 
36-40 ohms as theory says sit should.  The dipole acts as top loading to the 
tower even though it is not in any way connected to the tower.

With the arrangement you are suggesting, the coupling between the two 
feeders would be much closer than what I have between the tower and feeders.

Since, with the feeders shorted out and fed in parallel, both sides of the 
line should be at the same potential all the way to the top, assuming that 
the flat top is symmetrical. I would say it makes little difference whether 
the flat top section is shorted or not as far as antenna performance goes.

You might try setting it up so you can make an A-B comparison on 80m between 
your existing vertical tee setup and the dipole setup.  There are likely to 
be times and distances away where each would put out a better signal to the 
desired location.

But even if you separated the two feeders as you described, each feeder 
would still be closely coupled to the flat top, making it a vertical tee 
regardless of which feeder you actually attach to the antenna tuner.

Don k4kyv



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