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55952Re: DC-DC converter for Ensemble RX II

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  • n6gn
    Jun 3, 2011
      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
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