Topband: Compromise vertical loading questions

[Tom W8JI]

One additional point about this that I might not have expressed in enough 
detail.

When a top hat with significant capacitance compared to distributed 
capaciatnce along the radiator is involved, current tends to become very 
linear throughout the radiator no matter where any loading inductance is 
inserted.

Bjorn has a particularly extreme example for this, because the SRF of the 
vertical without  any inductor was 2.2 MHz.

<<The antenna is self resonant at 2.2 MHz and I use a coil wound on a water 
bottle to bring it down to 1.8. The coil appears to be about 8-10 uH 
according to online calculators.>>>

He only has 100 ohms of reactance-cancelling inductance, which further 
proves his statement that the antenna SRF is 2.2 MHz. While the amount of 
reactance has no direct bearing on distribution, the fact it is so low means 
current is pretty much all flowing into the hat wires.
Series reactances do not change distribution above the reactance because it 
is a series system. Shunting capacitances or reactances do. The only way 
current can change is through an electric field and displacement currents. 
The significant capacitance, in his case, is the hat.

The only two places where significant changes are possible without a 
significant height increase are:

1.) reducing foldback of the hat

2.) improving the ground system


73 Tom