[ARC5] 10 meter ARC-5s

[AKLDGUY .]

> One side effect will be that the tuning scale will become very different.
> Imagine adding a 1pF capacitor in series with a 1-10pF variable capacitor
> (this is just a thought experiment, ignore the unrealistic values).
>
> Most of the variation in C with the 1pF series capacitor added will be
> squashed into the low end of the variable capacitor's range.

You're not considering that the frequency has been raised. It takes quite a
jump in your way of thinking to understand what I'm suggesting.

I believe I posted a calculation, based on Ken's figure of tuning gang fully
meshed at 62 pF. I now understand that the 62 pF is for the 3-6 MHz ARC-5
receiver, not the 6-9.1 MHz unit.

However, let me go over that calculation again, using the same 62 pF.
Imagine there was a series capacitor of say 3 pF in the connection to each
gang in order to raise the frequency from 9 MHz to 30 MHz.

Let's assume each gang is 10 - 62 pF and stray capacitance of 25 pF.
Fully meshed to fully unmeshed is therefore 35 - 87 pF.

At full mesh, product over sum for series capacitors gives 87 x 3 / 87 + 3.
Result: 261 / 90 = 2.9 pF across the coil.

Fully unmeshed, product over sum for series capacitors gives 35 x 3 / 35 +
3.
Result: 105 / 38 = 2.7 pF across the coil.

The ratio, fully meshed to fully unmeshed is 2.7:2.9, which is 1.07.
Since we have achieved resonance at 30 MHz by addition of the series
capacitor, the frequency coverage is 28 MHz x 1.07 = 29.96 MHz.

This illustrates that the "squashing" of the tunable range does not take
place
because the frequency has been raised. The percentage change at the new
frequency is what counts.

73 de Neil ZL1ANM