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

April 1 post?

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

Did I leave out some information??

On Fri, 1 Apr 2005 18:00:45 -0500, "Charles Schuler"
wrote:


April 1 post?

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

Albert writes:

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

Did I leave out some information??

When the homework is due?

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On Fri, 1 Apr 2005 18:00:45 -0500, "Charles Schuler"
wrote:


April 1 post?

Albert wrote in message ...

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

Say what? That's completely Looney tunes.

N

Albert wrote:

}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.

"Stan" wrote in message
...
Albert wrote:

}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?

Unless he wants to create a circuit with negative Q.

--
N

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



On Sat, 02 Apr 2005 06:45:54 -0000,
(Stan) wrote:

Albert wrote:

}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.

Albert wrote in message ...
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.

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

"NSM" bravely wrote to "All" (02 Apr 05 23:30:41)
--- on the heady topic of " Q of this circuit?"

NS From: "NSM"
NS Xref: aeinews sci.electronics.repair:44791


NS Albert wrote in message
NS ... No, that is not an
NS 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.

NS Simple. A resonant circuit is like a baseball on a foot of rubber
NS band.
NS Your circuit is like a piece of bread attached to a piece of taffy.

NS Which one do you think is 'bouncier'?

No matter which reactance is greater it would still oscillate. The
problem is being able to drive it adequately since the inductor and
capacitor each has an impedance of only 1.1 ohms. For example, it
would require about 15 amps just to get 10 volts across either
element. IOW this circuit is more suited to being a trap than a tank.

The more desirable strategy is to use as much inductance as possible
without the resistance losses of the wire becoming significant. The
ratio of the inductive reactance to the resistive losses is called the
quality or Q-factor of the coil. Generally it is the coil which has
the worst quality factor thus usually only the coil's Q is considered.
Look up inductance calculation tables or programs to help design it.

An alternative to using a coil is to synthesize a really large
inductance using a gyrator or what is termed a GIC or General
Immitance Converter. This is often seen in audio equalizers and active
crossovers for the low frequency region but with a fast opamp it
should easily work at 17.8Khz.

A*s*i*m*o*v

.... Electrical Engineers do it with more frequency and less resistance.

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
--------------------

Albert wrote:
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



On Sat, 02 Apr 2005 06:45:54 -0000,
(Stan) wrote:


Albert wrote:

}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.