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Re: [softrock40] Re: DC-DC converter for Ensemble RX II

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  • Alan
    ... Subject: [softrock40] Re: DC-DC converter for Ensemble RX II ... It is not the only way. A ground loop is due to two, or more connections between the
    Message 1 of 22 , Jun 1, 2011
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      ----- Original Message -----
      Subject: [softrock40] Re: DC-DC converter for Ensemble RX II


      > Yesterday I have tried connecting the USB power and ground to the analog
      > power and ground in my Ensemble II RX. I used a small ferrite toroid with
      > about 10 turns of 26AWG pair (+5 and ground on 2 wires wound together) for
      > RF noise suppression.
      > I didn't see any additional RF noise, but the central peak became
      > prominent (60Hz and about 10-15 harmonics on each side). This is a classic
      > ground loop. The only way break the ground loop in this configuration is
      > to add isolation transformers to the audio output.

      It is not the only way.
      A ground loop is due to two, or more connections between the Softrock and
      computer.
      It is always possible to make this just one, difficult maybe, if you have
      not made it easy to experiment with removing the grounds.
      Start by breaking the ground in the audio lead.
      The best results I've had were by bonding everything to a good ground. I
      then found that introducing a ground loop made no difference.

      73 Alan G4ZFQ
    • n6gn
      This is just a note to the list to say that I had good luck with building a DC-DC converter to generate 12 VDC from the USB derived 4.3 VDC on a QRP2000 Si570
      Message 2 of 22 , Jun 3, 2011
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        This is just a note to the list to say that I had good luck with building a DC-DC converter to generate 12 VDC from the USB derived 4.3 VDC on a QRP2000 Si570 synthesizer and used as LO for a slightly modified Ensemble II RX.

        The synthesizer is essentially a stand-alone version of those in the SoftRocks. I got mine from KM5H. Since I had both the synthesizer and an Ensemble RX II that was xtal'd on 40M, I thought it would be handy to use the synth and to power it all from the single USB connection. The result requires only antenna input, USB connection and I/Q cable.

        In addition, I dropped R16 to ~8K ohms so the 0 dBm from the LVDS of the synth would drive it and also widened the Ensemble RX input BPF to become mainly a high pass filter with ~ 10 MHz corner. To do that I removed C4, made C3 162 pf and made L4 only 9 turns instead of the 34 it previously had as 40M filter.

        The results are better than I thought they would be. Though I built the DC-DC converter with SMT parts (dead bug mounted) keeping the total clustered and with short connections, I figured that there might be serious problems from the 500 kHz oscillator in the LT1372. As it turned out, there really weren't any particular problems even down on 160 and 80M (where the filter was rolled off some but still letting some signal through).

        If anyone else wants to do this, all I did was implement the example circuit from the data. See http://www.linear.com/product/LT1372.

        I'm now using it with an ASUS netbook and the package makes a portable all band receiver about the size of a sheet of paper.
        I think the Ensemble/synth pulls ~ 200 mA from the 5 VDC on the USB port, but I didn't actually measure current into the finished unit.

        Glenn n6gn
      • Alan Campbell
        OK, time for me to expose my ignorance again... Why insist on 12V output? Specifically, I m looking at the schematic for the Ensemble II and the only chip
        Message 3 of 22 , Jun 5, 2011
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          OK, time for me to expose my ignorance again... Why insist on 12V output?

          Specifically, I'm looking at the schematic for the Ensemble II and the only chip using the +12V is the 78L05 - which then spits out +5V. At up to 100mA (by datasheet).
          Anything over 7-8V is wasted in the 78L05 and can even cause thermal shutdown.

          I read one web page that mentioned using a 9V battery to run the Ensemble II.  Looking at the circuit for the LT1372, I'd suggest dropping R1 for a lower output voltage would be more efficient.
          Less power produced, less wasted.

          Still, as long as it works, that's the main thing. Experimenting can be a lot of fun.

          -- Alan Campbell
             PF95ie


          From: n6gn <n6gn@...>
          To: softrock40@yahoogroups.com
          Sent: Saturday, 4 June 2011 1:53 PM
          Subject: [softrock40] Re: DC-DC converter for Ensemble RX II

           


          This is just a note to the list to say that I had good luck with building a DC-DC converter to generate 12 VDC from the USB derived 4.3 VDC on a QRP2000 Si570 synthesizer and used as LO for a slightly modified Ensemble II RX.

          The synthesizer is essentially a stand-alone version of those in the SoftRocks. I got mine from KM5H. Since I had both the synthesizer and an Ensemble RX II that was xtal'd on 40M, I thought it would be handy to use the synth and to power it all from the single USB connection. The result requires only antenna input, USB connection and I/Q cable.

          In addition, I dropped R16 to ~8K ohms so the 0 dBm from the LVDS of the synth would drive it and also widened the Ensemble RX input BPF to become mainly a high pass filter with ~ 10 MHz corner. To do that I removed C4, made C3 162 pf and made L4 only 9 turns instead of the 34 it previously had as 40M filter.

          The results are better than I thought they would be. Though I built the DC-DC converter with SMT parts (dead bug mounted) keeping the total clustered and with short connections, I figured that there might be serious problems from the 500 kHz oscillator in the LT1372. As it turned out, there really weren't any particular problems even down on 160 and 80M (where the filter was rolled off some but still letting some signal through).

          If anyone else wants to do this, all I did was implement the example circuit from the data. See http://www.linear.com/product/LT1372.

          I'm now using it with an ASUS netbook and the package makes a portable all band receiver about the size of a sheet of paper.
          I think the Ensemble/synth pulls ~ 200 mA from the 5 VDC on the USB port, but I didn't actually measure current into the finished unit.

          Glenn n6gn



        • n6gn
          Alan, Probably a good point in general. 12 VDC isn t particularly magic. However it does potentially give a bit more headroom before distortion in the OpAmps.
          Message 4 of 22 , Jun 6, 2011
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            Alan,
            Probably a good point in general. 12 VDC isn't particularly magic. However it does potentially give a bit more headroom before distortion in the OpAmps. I'm surprised that they aren't run from it instead of the 5 VDC of the SR Ensemble RX design. Maybe I've missed something obvious though.

            Also, I don't know that there is a linear correlation between output voltage on the switching regulator and overall efficiency. At least, I'd suspect for very low outputs, even with all else equal (which it never is!) that diode drop in the switcher would begun to hurt.

            Still, if someone is looking for alternative ways of powering a SoftRock/Si570 combination there's no requirement to provide 12V.

            I think the most useful thing I found is that switching regulator hash needn't be a severe problem. I suspect that the switched capacitor DC-DC converter solutions - which generally are limited to 2x voltage- might work just as well as the inductive switcher I used.

            I'd say the good news is that it isn't difficult to combine existing SR hardware/synthesizers to make a small, portable, all-mode, general coverage receiver that has decent performance very inexpensively.

            Best,
            Glenn n6gn

            > OK, time for me to expose my ignorance again... Why insist on 12V output?
            >
          • The Silver Fox
            Just for reference: I ve run my softrocks with 9V DC power for a long time without any noticeable negative effects but I ll admit that I ve not pushed them to
            Message 5 of 22 , Jun 6, 2011
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              Just for reference:  I’ve run my softrocks with 9V DC power for a long time without any noticeable negative effects but I’ll admit that I’ve not pushed them to the limit on transmit.

              73’s

              Alan – W6ARH

               

              From: softrock40@yahoogroups.com [mailto:softrock40@yahoogroups.com] On Behalf Of n6gn
              Sent: Monday, June 06, 2011 8:10 AM
              To: softrock40@yahoogroups.com
              Subject: [softrock40] Re: DC-DC converter for Ensemble RX II

               

               



              Alan,
              Probably a good point in general. 12 VDC isn't particularly magic. However it does potentially give a bit more headroom before distortion in the OpAmps. I'm surprised that they aren't run from it instead of the 5 VDC of the SR Ensemble RX design. Maybe I've missed something obvious though.

              Also, I don't know that there is a linear correlation between output voltage on the switching regulator and overall efficiency. At least, I'd suspect for very low outputs, even with all else equal (which it never is!) that diode drop in the switcher would begun to hurt.

              Still, if someone is looking for alternative ways of powering a SoftRock/Si570 combination there's no requirement to provide 12V.

              I think the most useful thing I found is that switching regulator hash needn't be a severe problem. I suspect that the switched capacitor DC-DC converter solutions - which generally are limited to 2x voltage- might work just as well as the inductive switcher I used.

              I'd say the good news is that it isn't difficult to combine existing SR hardware/synthesizers to make a small, portable, all-mode, general coverage receiver that has decent performance very inexpensively.

              Best,
              Glenn n6gn

              > OK, time for me to expose my ignorance again... Why insist on 12V output?
              >

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