Richard Clark wrote:
"How many pF capacitance in your top hat?"

How many degrees in your vertical?
What`s the ground system?
What`s the periphery of your vertical?
What`s the surge impedance of your vertical?
What other loading are you using ?

ON4UN works examples in the 2nd edition of "Low-Band DXing". His
examples happen to have slightly more than 100 pF when there`s no
loading coil. I`ve seen other top loading capacitance values of 100-500
pF.

ON4UN`s capacitance hat, as used with a 40-foot vertical pipe on 160
meters which has a 166-microhenry loading coil at the top, has 43 pF.

XL must equal Xc in the antenna circuit because the antenna must be
resonant to maximize current and radiation.

The 19th edition of the ARRL Antenna Book says on page 6-36:
"For estimating the capacitance of a T antenna made of wires, an
approximation is to use 6 pF per meter for vertical wires, and 5 pF per
meter for horizontal wires." With parallel wires, the total capacitance
must be discounted when the wires are close together.

Best regards, Richard Harrison, KB5WZI