[ARC5] 400784741321

[AKLDGUY .]

> Now hold on a minute: what about the inductors? If all you do is reduce
the
> capacitance, the L/C ratio will be horrible, "Q" will be reduced,

Did I reduce the capacitance? Yes, I did by inserting series capacitance.
Did you reduce the capacitance? Yes, you did by removing plates.

Now, neither of us changed the inductance. Therefore, the LC ratio will be
horrible ***no matter what is done with the capacitance***.
Does that mean that the unit you have in your possession has bad Q?
Yes, and my suggested method will be no worse or better than yours since
we have both changed ONLY the *total* capacitance to get to 10m.

> and in
> addition, I don't see how that combo can resonate anywhere near 30 MHz,
> but instead, would resonate much lower in frequency.

Nope, it will resonate much higher. A series capacitor to the main capacitor
means less *effective capacitance* across the coil. The smallest capacitor
is dominant in a series circuit made up of capacitors.

> Besides, when the main tuning cap is fully unmeshed, the capacitance is
> already "low", on the order of a few pF as I remember it. Therefore, the
"L"
> must also be reduced.

The smallest capacitor is dominant in a series circuit made up of
capacitors,
therefore for the sole purpose of getting to 10m, the L need not be reduced.

> In my case, the tuning cap had already had all but one of the rotor plates
> removed. I worked with what I had.

Yes, we understand that and nobody including myself is criticizing you.

> Regarding the above: according to the manual, the main-tuning capacitor
> has a delta-C of 62 PFD, and the schematic (for the BC-455) suggests that
> the maximum capacitance for the tuning cap, C-4A/B/C is 62 pfd.
>
> Calculating on this basis the inductance of the coil(s), they should be
about
> 11.5 microH.
>
> Even at 3 pfd total that would tune to 27 MHz, and we haven't even begun
to
> look at L/C ratio yet.

Well, there you go !!!  A starting point for the value for the series
capacitor
approach suggested by me is 3 pF.

At full mesh, 62 pF with about 25 pF stray = 87 pF.
In series with 3 pF, the result is 87 x 3 / 87 + 3 = 261 / 90 = 2.9 pF.

At fully unmeshed, 3 pF with about 25 pF stray = 28 pF.
In series with 3 pF, the result is 28 x 3 / 28 + 3 =  84 / 31 = 2.7 pF.

Meshed to unmeshed, the capacitance change is now 2.9 / 2.7 = 1.07.
I'm not going to bother working out the square root relationship of that
1.07
capacitance ratio, but you will note that 28 MHz x 1.07 = 30MHz, so based on
your own figures it's in the right ball park.

As said, the smallest capacitor is dominant in a series circuit made up of
capacitors.

73 de Neil ZL1ANM