A good crystal band-pass filter for a single-sideband phone would be?

2.1 KHz.

From kj6prf:

This is the bandwidth your voice needs to sound decently like your voice over the radio.

A 500-Hz bandpass filter would filter out the bulk of your voice, making you sound strange and robotic.

A 5-kHz and 15-kHz filter would keep more information about the higher frequency components of your voice, which would sound truer to your actual voice, but the resulting signal would take up more bandwidth for a minor increase in sound quality. 2.1 kHz is the sweet spot for efficiency and sound fidelity.

For crystal filter information, please see the Science Direct site for the article on Crystal Filters

And, see the Engineering360 site for the article Crystal Filters Information

For more information, please see the Electronics tutorials site for the article Passive Band Pass Filter

Also, see the Mastered site for the article What Is A High Pass Filter & How to Use it in Mixing

And, see the site Electronics For U for the article Filters Using Op-Amps | Band Pass, Band Stop, High Pass & Low Pass Filter

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What are the three general groupings of filters?

High-pass, low-pass and band-pass.

For more information, please see the Electronics tutorials site for the article Passive Band Pass Filter

Also, see the Mastered site for the article What Is A High Pass Filter & How to Use it in Mixing

And, see the site Electronics For U for the article Filters Using Op-Amps | Band Pass, Band Stop, High Pass & Low Pass Filter

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What is an m-derived filter?

A filter that uses a trap to attenuate undesired frequencies too near cutoff for a constant-k filter.

There are the m- and k-constant filters. The k one produces a sharp drop (cut-off) edge.

The m-derived filter matches the impedance. Since the attenuation increases rather quickly at the cutoff frequency, the filter's output stays the same in the pass band.

See Wikipedia's article on m-derived filter, and the article on Constant k filter

Also, see the Electronics Tutorials site for the article on m Derived Filter and the article on Constant K Filter

And, see the EEEGuide site for the article on m Derived Filters

Please see the Electronics Notes site for the article What is a Constant-K Filter: the basics

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What is an advantage of a constant-k filter?

It has high attenuation of signals at frequencies far removed from the pass band.

There are the m- and k-constant filters. The k one produces a sharp drop (cut-off) edge.

The m-derived filter matches the impedance. Since the attenuation increases rather quickly at the cutoff frequency, the filter's output stays the same in the pass band.

See Wikipedia's article on m-derived filter, and the article on Constant k filter

Also, see the Electronics Tutorials site for the article on m Derived Filter and the article on Constant K Filter

And, see the EEEGuide site for the article on m Derived Filters

Please see the Electronics Notes site for the article What is a Constant-K Filter: the basics

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What are the distinguishing features of a Butterworth filter?

It has a maximally flat response over its passband.

Using only capacitors, the filter's shunt and series element impedances produce a constant (flat) output of all frequencies.

See Wikipedia's article on Butterworth filter

Please see, the Electrical 4 U site for the article Butterworth Filter: What is it? (Design & Applications)

Also, please see the Electronics Notes site for the article on What is a Butterworth RF Filter - the basics

And, please see the All About Circuits site for the article on Understanding Butterworth Filter Poles and Zeros

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