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Re: [softrock40] USB power for SRv9? - conclusions

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  • kazunori miura
    Hello, all I am making SDR with USB power supply. To reject noise from PC, it is needed comon mode filter and ripple filter. The result is here.
    Message 1 of 10 , Mar 31, 2009
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      Hello, all

      I am making SDR with USB power supply.
      To reject noise from PC,
      it is needed comon mode filter and ripple filter.
      The result is here.

      http://zao.jp/media/blogs/b/P1010799.JPG

      But little noise is still left around center frequency.
      these noise is comming from PC via shield of USB cable.

      best 73

      JA7TDO

      Jeff Blaine ????????:
      > Bob and Tony,
      >
      > My original tests were made using a USB and line-in tap on my docking
      > station.
      >
      > Tonight I moved to a usb/line-in pair on the laptop it'self and the
      > difference is HUGE...
      >
      > S9 from the XG2 vs. noise floor (just sliding the passband over a bit)
      > results:
      >
      > Dock DIRECT Improvement
      > ----------------------------------------------
      > 80m: 45dbm 60dbm +15dbm
      > 40m: 40 54 +14dbm
      > 20m: 43 56 +13dbm
      >
      > I am shocked to see such a huge difference.
      >
      > Based on these results, I took some quick measurements on the external
      > USB vs internal, and the external line-in vs. internal. About 10dbm of
      > the improvement is from the line-in, and 5dbm is from the USB.
      >
      > And that was quite a nice surprise...
      >
      > 73/jeff/ac0c
      >
      > k8ki/Bob wrote:
      >> I don’t think there’s a lot of hope in expecting good sensitivity if
      >> the supply voltage is lowered. The FST3253 needs 5v to run properly.
      >> It was designed for reliable digital service, and is a fairly noisy RF
      >> device. I do think that 2N3904 could instead be used as a
      >> preamplifier—it’s quite capable of achieving a 5 dB noise figure
      >> throughout the hf region.
      >>
      >> Bob/k8ki
      >>
      >> * From: * softrock40@yahoogro ups.com [mailto: softrock40@yahoogro
      >> ups.com ] *On Behalf Of *Tony Parks
      >> *Sent:* Monday, March 30, 2009 12:17 PM
      >> *To:* softrock40@yahoogro ups.com
      >> *Subject:* Re: [softrock40] USB power for SRv9? - conclusions
      >>
      >> It would be interesting to try an NPN transistor in the 5 volt USB
      >> power line to the v9.0 receiver 5 volt bus. The collector of the NPN
      >> transistor would connect to the USB 5 volt line. A 10 ohm resistor
      >> from the USB 5 volt line would connect to the base of the NPN
      >> transistor. From the base of the NPN transistor to circuit grround
      >> would be a 47 uF cap and a 0.1 uF cap. The emitter of the NPN
      >> transistor would then feed the 5 volt bus on the v9.0 board.
      >>
      >> The power loss in the NPN transistor would be less than 100 mW so a
      >> transistor such as a 2N3904 could be used.
      >>
      >> 73,
      >>
      >> Tony Parks
      >> kb9yig@gmail. com <mailto:kb9yig@...>
      >>
      >>
      >>
      >> On Mon, 2009-03-30 at 11:58 -0500, Jeff Blaine wrote:
      >>
      >>> Jeff Blaine wrote:
      >>>> Conclusions and results following comments from the group and some
      >>>> bench time...
      >>>>
      >>>> Before modification, benchmarking a S9 level (XG2) and the noise
      >>>> floor, and making a simple subtraction to establish the noise floor,
      >>>> my laptop internal sound card and the v9 + BPF had about a 40-44 db SN
      >>>> difference.
      >>>>
      >>>> 1. At a 5.0V usb power input, the performance of the rig is hurt most
      >>>> by the voltage drop. It's a bigger impact than the noise pickup from
      >>>> the PC side.
      >>>>
      >>>> The diode and the regulator drop-out just kill the noise floor. To
      >>>> make the best of this, I removed the diode and replaced the 7805 with
      >>>> a LD1084 adj set for 4.25v terminal voltage. With 5.06v in, the rig
      >>>> saw about 3.94v (usb voltage a bit low for the regulator to work
      >>>> properly).
      >>>>
      >>>> Under this condition, the SN difference was:
      >>>>
      >>>> 80m: 37db
      >>>> 40m: 27db
      >>>> 20m: 22db
      >>>>
      >>>> Conclusion: The combination of lower voltage + USB noise cost about
      >>> 20db!
      >>>> 2. To establish the contribution of the USB vs. the lower voltage, the
      >>>> regulator input was moved over to a battery source. 6.37v in, 4.23v
      >>>> out (meaning the regulator also had enough voltage to work properly).
      >>>>
      >>>> 80m: 35db
      >>>> 40m: 31db
      >>>> 20m: 35db
      >>>>
      >>>> Conclusion: The slightly higher voltage + battery source improved the
      >>>> noise floor by 2-13db. Higher frequency, more benefit.
      >>>>
      >>>> 3. Resetting the regulator voltage to 5.34v, under battery power:
      >>>>
      >>>> 80m:: 45db
      >>>> 40m:: 40db
      >>>> 20m: 43db
      >>>>
      >>>> Conclusion: An increase in Vcc from 4.23 --> 5.34 improves the noise
      >>>> floor by 5-10db. Case is similar to the original regulator & external
      >>>> supply used as a baseline.
      >>>>
      >>>> 4. Removed regulator. Add L/C networks to USB supply lines. Liberal
      >>>> use of 0.1uf chip caps. Now USB powered:
      >>>>
      >>>> 80m: 44db
      >>>> 40m: 39db
      >>>> 20m: 41db
      >>>>
      >>>> Conclusion: USB power with some filtering effort has brought the USB
      >>>> vs. external battery performance to within a 2db noise floor increase
      >>>> of battery power alone.
      >>>>
      >>>> Given the intention of this rig (travel use), the 2db is a reasonable
      >>>> trade-off considering the advantage of not having an external power
      >>>> source to contend with.
      >>>>
      >>>> 73/jeff/ac0c
      >>>>
      >>>>
      >>>>
      >>>> Jeff Blaine wrote:
      >>>>> Has anyone tried to run the SRv9 powered only by the USB port?
      >>>>>
      >>>>> Meaning - one port to run the attiny - and another port for power only
      >>>>> (bypassing the 7805).
      >>>>>
      >>>>> The SR is normally setup with +12v but the +12v unregulated line is
      >>>>> unused presently. And the current drain is well within the 500ma per
      >>>>> port USB spec max.
      >>>>>
      >>>>> 73/jeff/ac0c
      >>>>>
      >>>>>
      >>>
      >>>
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