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Low pass filters

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  • Chuck
    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
    Message 1 of 11 , Jul 4, 2011
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      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
    • JOHN GREUSEL
      Chuck, I could be wrong but I believe the correct approach is to put filters for all bands you re going to use after the amplifier (pennywhistle) I don t think
      Message 2 of 11 , Jul 4, 2011
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        Chuck,

        I could be wrong but I believe the correct approach is to put filters for all bands you're going to use after the amplifier (pennywhistle) I don't think the built in filters for 30 and 20 will be sufficient for adequate suppression after the amplifier. If you want to design and construct your own system why don't you put in a three position switch and have a new BP filter for each band? They're simple enough to create.

        John
        KC9OJV

        From: Chuck <chuck@...>
        To: softrock40@yahoogroups.com
        Sent: Monday, July 4, 2011 7:12 AM
        Subject: [softrock40] Low pass filters

         
        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



      • Chuck
        John, That is where I m trying to get to. I was just looking at the builders notes to figure out how to go about it. The Elsie results were not what I expected
        Message 3 of 11 , Jul 4, 2011
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          John,
          That is where I'm trying to get to. I was just looking at the builders notes to figure out how to go about it. The Elsie results were not what I expected so understanding what to expect from my own filter design is job one.
          Thank you,
          Chuck Lippmeier

          --- In softrock40@yahoogroups.com, JOHN GREUSEL <greusel@...> wrote:
          >
          > Chuck,
          >
          > I could be wrong but I believe the correct approach is to put filters for all bands you're going to use after the amplifier (pennywhistle) I don't think the built in filters for 30 and 20 will be sufficient for adequate suppression after the amplifier. If you want to design and construct your own system why don't you put in a three position switch and have a new BP filter for each band? They're simple enough to create.
          >
          > John
          > KC9OJV
          >
          >
          > ________________________________
          > From: Chuck <chuck@...>
          > To: softrock40@yahoogroups.com
          > Sent: Monday, July 4, 2011 7:12 AM
          > Subject: [softrock40] Low pass filters
          >
          >
          >  
          > 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
          >
        • JOHN GREUSEL
          Chuck, I was just trying to imagine a simple means of testing your filter design. If you had a antenna analyzer and another softrock receiver you could emit
          Message 4 of 11 , Jul 4, 2011
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            Chuck,
            I was just trying to imagine a simple means of testing your filter design.
            If you had a antenna analyzer and another softrock receiver you could emit from the analyzer (tune through the area of interest) and receive with the softrock and see the BP on the SR spectrum. I think that would work.

            John
            KC9OJV

            From: Chuck <chuck@...>
            To: softrock40@yahoogroups.com
            Sent: Monday, July 4, 2011 7:59 AM
            Subject: [softrock40] Re: Low pass filters

             
            John,
            That is where I'm trying to get to. I was just looking at the builders notes to figure out how to go about it. The Elsie results were not what I expected so understanding what to expect from my own filter design is job one.
            Thank you,
            Chuck Lippmeier

            --- In softrock40@yahoogroups.com, JOHN GREUSEL <greusel@...> wrote:
            >
            > Chuck,
            >
            > I could be wrong but I believe the correct approach is to put filters for all bands you're going to use after the amplifier (pennywhistle) I don't think the built in filters for 30 and 20 will be sufficient for adequate suppression after the amplifier. If you want to design and construct your own system why don't you put in a three position switch and have a new BP filter for each band? They're simple enough to create.
            >
            > John
            > KC9OJV
            >
            >
            > ________________________________
            > From: Chuck <chuck@...>
            > To: softrock40@yahoogroups.com
            > Sent: Monday, July 4, 2011 7:12 AM
            > Subject: [softrock40] Low pass filters
            >
            >
            >  
            > 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
            >



          • Tony Parks
            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
            Message 5 of 11 , 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. 

              73,
              --
              Tony Parks
              kb9yig@...
              http://www.kb9yig.com
              
              


              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




            • Chuck
              Tony, The result being at least 43dB down: Is that because the filter drops any second harmonic 11dB but the harmonic is already less than the difference i.e.
              Message 6 of 11 , Jul 4, 2011
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                Tony,
                The result being at least 43dB down: Is that because the filter drops any second harmonic 11dB but the harmonic is already less than the difference i.e. 43-11=32dB down from the fundemental?

                --- In softrock40@yahoogroups.com, Tony Parks <kb9yig@...> wrote:
                >
                > 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.
                >
                > 73,
                > --
                >
                > Tony Parks
                > kb9yig@...
                > http://www.kb9yig.com
                >
                >
                >
                >
                > 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
                > >
                > >
                > >
                > >
                > >
                >
              • Chuck
                John, Testing for me wouldn t be a problem as I have the Signalhound Spectrum Analyzer w/ the tracking generator and a VNWA, as well as big box synthesizers
                Message 7 of 11 , Jul 4, 2011
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                  John,
                  Testing for me wouldn't be a problem as I have the Signalhound Spectrum Analyzer w/ the tracking generator and a VNWA, as well as big box synthesizers and power meters.

                  However, I don't think I would need the Antenna Analyzer in your proposal. The TX in a second ensembleRXTX can put out a toneusing Rocky.
                  Chuck Lippmeier
                  --- In softrock40@yahoogroups.com, JOHN GREUSEL <greusel@...> wrote:
                  >
                  > Chuck,
                  > I was just trying to imagine a simple means of testing your filter design.
                  > If you had a antenna analyzer and another softrock receiver you could emit from the analyzer (tune through the area of interest) and receive with the softrock and see the BP on the SR spectrum. I think that would work.
                  >
                  > John
                  > KC9OJV
                  >
                  >
                  > ________________________________
                  > From: Chuck <chuck@...>
                  > To: softrock40@yahoogroups.com
                  > Sent: Monday, July 4, 2011 7:59 AM
                  > Subject: [softrock40] Re: Low pass filters
                  >
                  >
                  >  
                  > John,
                  > That is where I'm trying to get to. I was just looking at the builders notes to figure out how to go about it. The Elsie results were not what I expected so understanding what to expect from my own filter design is job one.
                  > Thank you,
                  > Chuck Lippmeier
                  >
                  > --- In softrock40@yahoogroups.com, JOHN GREUSEL <greusel@> wrote:
                  > >
                  > > Chuck,
                  > >
                  > > I could be wrong but I believe the correct approach is to put filters for all bands you're going to use after the amplifier (pennywhistle) I don't think the built in filters for 30 and 20 will be sufficient for adequate suppression after the amplifier. If you want to design and construct your own system why don't you put in a three position switch and have a new BP filter for each band? They're simple enough to create.
                  > >
                  > > John
                  > > KC9OJV
                  > >
                  > >
                  > > ________________________________
                  > > From: Chuck <chuck@>
                  > > To: softrock40@yahoogroups.com
                  > > Sent: Monday, July 4, 2011 7:12 AM
                  > > Subject: [softrock40] Low pass filters
                  > >
                  > >
                  > >  
                  > > 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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