NESCAF Audio Filter
NESCAF Audio Filter Filed in homebrew on Jan.29, 2012 A couple of months ago, I dug out an old kit from the shelf to give the grandsons something to build while they were spending the day. They soldered most of the components on it, but didn’t have enough time to finish it. So now, I cleared off the bench once again, and finished the NESCAF Switched Capacitor Audio Filter. This is a primarily a CW audio filter, with some unique characteristics. You can smoothly vary the bandwidth and center frequency for the filter, which makes for very easy operating. NESCAF Audio Filter The NESCAF audio filter is kitted by the New England QRP Club. It is intended to be a CW filter with continuously variable bandwidth from about 90 hz to about 1500 hz. The center frequency is adjustable from about 150 hz to about 1000 hz. The filter uses a Switched Capacitor Audio Filter Chip (MF10, LMF100 or LTC1060 chip). It uses a 555 timer to create a square wave to feed the Switched Capacitor