Re: High Q caps for 60 Khz loop antenna?

TRABEM wrote:
John Popelish wrote:
Is there any possibility that you could add turns to your loop, to lower the size of the capacitor needed? 

> Hi John,
>
> The loop is already bigger then my house and buying the large diameter
> wire to make it was not cheap. Buying an additional length just to add
> another turn would not be easy on me physically.

All this makes sense.

> Further, the R(ac),
> and therefore the Q would suffer since the loops resistance is now
> doubled by the addition of a second turn.

This, however, doesn't, necessarily. The resistance would double, but the inductance would quadruple. The impedance would also quagruple from about 119 ohms to 476 ohms, so the Q would roughly double when tuned with a .055 uF capacitor. This, of course, neglects the loading effect of the receiver input resistance and the radiation resistance of the loop, and the eddy current loading of nearby conducting objects.

> I am going to feed this into a quadrature front end, which has a
> problem with harmonics getting into the receiver. My hope is to use
> the loop as the sole tuning for the front end of the receiver, so
> maintaining the highest possible Q is imperative.

Understood.

> In terms of labor and cost, it is much more practical to use a
> larger value capacitor to get higher Q than it would be to use
> larger cable and more turns of it for the loop.

I can certainly see the cost advantage. Even an expensive capacitor is probably cheaper than more wire.

> So, I will try to stick with the larger diameter single turn loop,
> which I why I asked for suggestions on which type of capacatior
> to buy to resonate the loop with.
(snip)

Makes lots more sense, now that I understand you are not using a ferrite rod antenna.

.

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