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SAW filters


Kevin Weddle
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Hi Kevin,
SAW filters have been popular for awhile for their use in cable TV boxes, TV transmitters and TV sets. In the olden days, those systems used many tuned LC filters to achieve the "funny response" that is required for sharp cutoff of the side of the picture carrier that isn't transmitted (vestigal single-sideband), a flat response for the desired channel and notch filters for adjacent channel picture and sound carriers on both sides of the bandpass in order to avoid interference. The LC filters were difficult to tune because adjusting one would affect the rest.
Now a SAW filter accurately does all that without needing any adjustment.
I can't think of any function that would be useful for a hobbiest, unless they want to make one of the devices (listed above) from scratch.

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Hi Andrew,
A crystal is a tuned circuit, that's why a crystal oscillator works. It is a low impedance series LC circuit at one frequency and a high impedance parallel LC circuit at a near frequency.
If you use a crystal as a filter, its bandwidth is so narrow that it wouldn't receive much modulation (just CW morse code).

AM-FM radios use "ceramic filters" in their IF amplifier that are designed with a certain fairly wide, flat bandwidth and steep skirts.
A ceramic filter is similar to a crystal.

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