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56506Re: [softrock40] Low pass filters

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  • Tony Parks
    Jul 4, 2011
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      Hi Chuck,

      The external LP filters are needed with the multi-band version of the RXTX Ensemble to reduce the second harmonic of the lowest band by about four dB or so.  This results in all spurious outputs being at least -43 dB down. 

      Tony Parks

      On Mon, 2011-07-04 at 12:12 +0000, Chuck wrote:
      Lately, I've been thinking about the low pass filters that Robby calls out in his section on external coonnections in the Ensemble RXTX builders notes. Since I built the 20/30/40 veersion I'll be interested in the 40m LPF. I just downloaded and installed Elsie, a very nice filter design program, and entered the values Robby cals out. I'm seeing around -11dB at 14MHz. I thought this was supposed to be -43dB from the fundemental of 7MHz. Have I found a bug in the design or, more likely, where have I gone wrong in my thinking?

      Thank you,
      Chuck Lippmeier

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