The filter we're talking about is sufficiently wide to accomodate any drift, and since the sampling is at a couple of hundred KHz, the filters are very simple.
Joe --- On Thu, 9/18/08, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote: From: [EMAIL PROTECTED] <[EMAIL PROTECTED]> Subject: Re: [Repeater-Builder] Re: CTCSS highpass filter paper To: [email protected] Date: Thursday, September 18, 2008, 9:40 PM Hi All, Please note some items that should be considered when making a "commercial version" 2175 notch filter. Not all remotes and consoles generate a precise 2175 Hz tone. Older units use LC oscillators that can drift, while newer ones are crystal controlled and are more accurate. A switched capacitor filter IC has a tolerance, expressed as a clock to corner ratio, which can be as much as 1.5%. So you have a encoder that shifts and a decoder that shifts. How do you guarantee that the notch has sufficient depth, say, 50 to 60 dB, regardless of the encoder brand or age so that the operator doesn't complain about the tone in her ear? Rather than build an adjustable decoder, which needs to be calibrated and has insufficient temperature stability, you build a crystal-controlled decoder. And you choose the Q of the filter so it delivers a notch of sufficient depth over a sufficient range of frequencies. And since it's a sampled data system, don't forget the antialias and reconstruction filters. 73, Bob, WA9FBO S-COM, LLC In a message dated 9/18/2008 7:31:15 P.M. Mountain Daylight Time, skyislandpage@ yahoo.com writes: Walter, that same chip could easily be built up on a small circuit board to give a 2175 notch, with a very sharp response. Could probably build one up for $20 or so. Joe --- On Thu, 9/18/08, ka1jfy <walter.howard. [EMAIL PROTECTED] com> wrote: From: ka1jfy <walter.howard. [EMAIL PROTECTED] com> Subject: [Repeater-Builder] Re: CTCSS highpass filter paper To: Repeater-Builder@ yahoogroups. com Date: Thursday, September 18, 2008, 3:17 PM Not real interested in a PL filter, but my agency [hello Joe M] would be REAL interested in a commercial version of the notch filter. We currently put either a Vega passive [$150] or Midian active [$60] 2175 notch in every repeater we build up. Walter KD7BJJ Phoenix, AZ Looking for simple solutions to your real-life financial challenges? Check out WalletPop for the latest news and information, tips and calculators.
