Topband: Vertical vs. Shunt-Fed Tower and Detuning

[Ryszard Tymkiewicz]

After many frustrating experiences with unwelcome interaction between 
various 160 antennas and towers, I am thinking about going back to 
basics by removing all the other 160 wires, and shunt feeding the 110 
foot tower (which has a number of yagis on it). All else being equal 
(such as ground system), are there reasons why a shunt-fed tower would 
work differently than a vertical of the same height, on an insulated base ?
73,
Steve, N2IC
_______________________________________________
Topband reflector - topband at contesting.com


Hi Steve and All,
I was writing about my tests a few years ago but maybe it will be useful for some...
I was using a Half Sloper on  20m high tower with TH6DXX on the top. I was very
satisfied with this antenna and it "gave" me 280 DXCC that time. Anyway I decided to
check how  shunt fed tower will behave...I had relays on wires of sloper so I was
able to make tests during QSOs in a real time. After more than 30 QSOs with stations
of a distance above 5000 km I decided to stay with shunt fed system..95 % correspondents
gave me 1 to 2 S better report when using the tower. I have to add the tower is only 4m from 
my house ( 9m high).
Regarding detuning... I have K9AY about 30m from a tower and I was not very satisfied with it
so I suspected the tower affects it. I made detuning described by John ON4UN (LB DXing
fourth edition page7-94 fig.7-135) . I did it for both 80 and 160m so I'm able to switch 
it on TB on and off ( switching to 80m).. the difference is huge , the null at the back can be worse
even 2 S when the antenna is not detuned.

                            73 GL
                            Rys
                           SP5EWY