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Q of this circuit?

I need to have an estimate of the Q for a parallel tuned circuit consisting of a 10 microhenry air wound coil and an 8.2 microfarad electrolytic cap. Coil parameters are below.

DC Resistance 0.16 Ohms Wire Gauge 24 AWG Wire Diameter 20.1 mils (1 mil = .001 in) Coil Length 1 in Coil Inner Diameter 0.5 in Coil Outer Diameter 0.54 in Average Turn Diameter 0.5 in Wire Length 6.02 feet Copper Weight 0.01 pounds Turns 46 Levels 0.92 Turns/Level 49.75

The circuit will feed into an mk484 AM radio chip (or it's very similar brother, the LMF501) which has an input impedance of (about)

100 K ohms.

I'm sure this is easy to do, but I can't figure out how the ac resistance of the cap impacts the Q calculation.

Thanks,

A
Reply to
Albert
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April 1 post?

Reply to
Charles Schuler

No, not really................

Did I leave out some >

Reply to
Albert

Resonates at 18 kHz and still seems like April Fool to me!

Reply to
Charles Schuler

When the homework is due? :)

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Reply to
Sam Goldwasser

... 10 microhenry air wound coil and an 8.2 microfarad electrolytic cap...

Say what? That's completely Looney tunes.

N
Reply to
NSM

}I need to have an estimate of the Q for a parallel tuned circuit }consisting of a 10 microhenry air wound coil and an 8.2 microfarad }electrolytic cap.

An "8.2 microfarad" cap in an RF tuned circuit?

Please re-check...perhaps you meant 8 uuf?

Stan.

Reply to
Stan

Unless he wants to create a circuit with negative Q.

--
N
Reply to
NSM

No, that is not an error. I meant 8.2 uf, not 8.2 uuf.

The 10 uh coil is easier to make, so I wanted to use a small inductor and a large capacitor. It should resonate at 17.8 Khz, which is the frequency I am building a receiver for.

Why does everyone think this is a joke and/or an error? This is a legitimate question. I gave (what I thought) was the specifications needed to arrive at a value for loaded Q....or at least a rough estimate.

Thanks to all,

A

Reply to
Albert

Simple. A resonant circuit is like a baseball on a foot of rubber band.

Your circuit is like a piece of bread attached to a piece of taffy.

Which one do you think is 'bouncier'?

--
N
Reply to
NSM

Albert -

Electrolytic caps are really not very good in resonant circuits.

First, you must not allow the cap voltage to go negative - which means you must ensure that there is a DC bias at least as great as the peak voltage of the sine wave that will exist there.

In addiion, they have a fair amount of series resistance (which will drag down the Q of the overall circuit). And because of their construction, they also have a fair amount of parasitic inductance - probably well above 10 uH. Just as a general statement, at KHz frequencies, you probably should be thinking about mH coils and nF caps.

Bill

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Albert wrote:

Reply to
Bill Jeffrey

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