variable cap options

[p.larner]

my main vc in my atu is large with plates about 3inches x 1.5 inches,the max pf was 1000pf but its min was to high for higher bands,i removed about 2/3 of the plates so now its 300pf ish max but the min c is still to high,I have another cap i can build up with  plates roughly half the size,would that have a lower min c if i built it for the same say 300pf max c?

[vk4ffab]

can build up with  plates roughly half the size,would that have a lower min c if i built it for the same say 300pf max c?

Its not the plate size that is critical for minimum capacitance, its the amount of overlap that remains when the plates are in the fully disengaged state and the number of plates in the stack.

QUESTION. What is the minimum capacitance you require for tuning on higher bands?

[p.larner]

Tbh i dont know the min c needed,its min now is about 30pf 10 would be ok by the feel of it i guess,i may remove another plate and test,73.

[p.larner]

so would a smaller number of large plates be better than the same area divided by a larger number of smaller plates for the same surface area provided they are not in mesh?for lower min c?.

[vk4ffab]

so would a smaller number of large plates be better than the same area divided by a larger number of smaller plates for the same surface area provided they are not in mesh?for lower min c?.

I honestly do not know. But, also check the minimum inductance from the inductor as well. Remember that an antenna tuner it a relationship between L and C. Bust out your LCR meter and measure it as well. Cap might be borderline fine if the L goes low enough.

As to your above question, give this calculator a try, you can get a rough idea of the minimum and maximum cap before you pull things to bits.

https://www.66pacific.com/calculators/capacitor-calculator.aspx

[A.Z.]

and then

https://www.utmel.com/tools/series-and-parallel-capacitor-calculator?id=25

try a 30pF fixed cap (switched) in series to the VC