where can I find a tunable notch filter circuit?
436468
More info is needed. \n\nWhat is the pass band frequency, what is the spectral content of the input signal. Ideally how steep do you want it?
194790
See the link for a tutorial on phase shifters.  If you know how to design one you will know what they do, right?
161589
Try this link: http://www.crystalinks.com/shc.html
86464
I'm afraid there are none such available except by the company that sells it. Try them, or do it yourself.
105925
DUDE CHECK OUT GROUNDEFFECTS.COM OR STREETCONCPET.COM FRIGIN COOL  KITS ILL TELL YA!
477486
http://www.analogX.com
682702
www.tessco.com\n\nWhat type of signal are you trying to enhance??
62935
sure, what you want is an IR filter, which you can pretty easily get from any optics supplier.  here are a wide range of choices from melles-griot, but they're kinda expensive.  however they are quality professional-grade filters.\n\nhttp://shop.mellesgriot.com/products/optics/optics.asp?plga=051408&CatID=10222&mscssid=&Page=All\n\nhere are some cheaper versions with slightly less clean spectra, but probably still functional depending on your needs:\nhttp://shop.mellesgriot.com/products/optics/optics.asp?plga=085680&CatID=1023&mscssid=\n\nyou can probably get some for cheaper if you hunt around on the web.  just be careful you aren't getting the opposite of what you want - a stop-visible/pass-IR filter, which is used a lot in infrared photography.
754291
http://www.rselectronics.com
1111658
http://www.epanorama.net/circuits/vga2rgbs.html
258659
go to hardwarezone.com.  perhap you can find it there..
617956
http://1accordion.net/tuning.html
977381
Can you get your hands on a Flux Capacitor?
312735
Try a damping circuit.
1065629
try smartparts web sight
409693
i think you can go to Best Buy.com or circuit city.com or go to the store staples. Or plan b,EBAY!!!!
137404
This is true, usually the filters are made by Inductances and Capacitors.\nOriginally the radios used a variable capacitance to select the frequecy, now they used a PLL; is an electronic device that "lock" the radio in the desired frequency.