Topband: Shunt-Fed-Tower matching issue

[tsaitou at mta.biglobe.ne.jp]

Hello Topbander,


My Shunt-Fed-Tower works well in a reasonable fashion 
so far.  (66 feet + 5el Tri-bander 3 feet above the top)  

After adding a few buried radials as for CQ-WW-CW,
I encountered following strange situation. 
(I don't think those radials caused this issue though..)

With using MFJ-259B,I can easily found 50 ohm(real part) 
spot after changing Gamma-wire's position (distance 
from the tower). Junction point of gamma wire is top of 
the tower. Then,I changed the value of gamma capacitor.
Although I can reach zero-reactance spot as well,but found 
one serious issue. What I experienced is the decrease of 
the real part (not 50 ohm any more,but it moves down to 
20ohm or 25ohm..etc.)  

While I need more trial,I'm confused a little.
Does anyone encounter this kind of phenomenna?


73,Tosy-JE1TSD