Topband: Tower Detuning

[Tree]

On Sun, Feb 16, 2003 at 06:05:26PM -0800, Michael Tope wrote:

> Questions:
> 
> 1.)  What sort of peaking should we expect to see on the scope
> when the current transformer is placed on the shunt arm (We
> see about a 4x increase in voltage when the capacitor is set
> at about half scale [150pf] as compared to the readings we
> get when the capacitor is set at either min or max capacitance)?

When I did this, I had a pretty obvious peak in current when running
50 watts or so.

> 2.) Should we bother insulating the bottom set of guys (I am
> concerned that the fact that they are not insulated is messing
> up our ability to effectively detune the tower).

I think reducing the number of wires that can conduct is a smart
thing.  At least insulate from the tower, and maybe again once
or twice.

> 3.) Do we need to bond the shields of the hardlines to the tower
> electrically near the base of the tower (the hardlines are physically
> attached with tape to the tower legs all the way down to the base
> of the tower, but are not bonded electrically)?

I don't think you need to as long as they are either inside or
taped to the tower well.

> 4.) We did not see a corresponding dip (it was very very
> slight) when we put the current transformer around the leg of
> the tower below the junction point of the shunt arm and the
> tower leg. Why is this? Could it be that some of the current
> is flowing in the other two tower legs or on the hardline
> shields or down the bottom guys wires since they aren't
> insulated)?

This sounds like a low Q situation.  Maybe you should try shortening
the height that you attached the wire to.

Tree