[ARC5] 400784741321

[Kenneth G. Gordon]

On 16 Oct 2014 at 12:28, AKLDGUY . wrote:

> I pointed out the proper way to do it many months ago. I don't know whether the
> Brits did it that way or not, but will repeat here how it should be done.
> 
> Do NOT remove plates from the tuning capacitor to raise the frequency !!!
> Instead, solder a small value capacitor in series with each gang of the
> tuning capacitor. The value must be determined by experiment until 30 MHz is
> reached with the tuning capacitor plates nearly fully open.

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

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 addition of the small capacitor causes an immediate rise in
> the frequency

Of course.

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

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.

Ken W7EKB