filtering

[Kevin Weddle]

From what I gather, resonance allows for only about 65db/decade filtering. Is it okay to operate an LC away from resonance? Less filtering means less loss if you aim to conserve your bandwidth.

 

[audioguru2]

The Q of a tuned LC circuit determines its bandwidth. A high Q has a very narrow bandwidth and very steep sides. Cascaded filters increases the overall Q.

Ceramic filters are used for wide bandwidth and steep sides in the IF amplifier of FM radios. SAW filters are used for TVs.

View attachment 40215

 

[Kevin Weddle]

Thank you. Do you know of LC's being operated out of resonance? LC filtering is still popular.

 

[walid1]

Hi guru

SAW filters are used for TVs.

what are SAW filters?

 

[audioguru2]

what are SAW filters?

A Surface Acoustic Wave is sent across a tiny crystal that has many breaks in it and the result is a response that has an accurate center frequency, low insertion loss, flat bandpass and very steep sides.
Google has too much information about them.

 

[Kevin Weddle]

Yes, SAW filters look great. Many LC circuits don't involve resonance, but many do. I was suggesting the fact that a good signal filter can be made without using resonance. Is a nonresonant LC signal filter a stupid idea?

 

[audioguru2]

You can make a lowpass filter and a highpass filter with LC circuits. Their load must not change resistance or they become series-resonant and short the source.
Radio circuits and speaker crossover networks have LC lowpass and highpass filters.

 

[Kevin Weddle]

Useful knowledge, I appreciate it. If your right!