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Monday, April 27, 2015

SDR Dongle Modified for HF. Watch it work on 40 meters (VIDEO)

With SPRAT 162 by my side, armed with an FT37-43 trifilar wound transformer, I popped open the RTL-SDR dongle.  I had hopes of being able to solder two tiny wires to the unused input pins (3 and 4) but I quickly realized that I was NOT going to be able to do that -- they are far too small for me to work on.  So I did what Ken Marshall G4IIB did:  I took out the SMT caps going to pins 1 and 2 and soldered two small wires there.  This will limit this dongle to HF only -- if I want VHF/UHF I'll just spend another $13 dollars!  You can see the results in the video above.

I used the yellow stuff to hold the wires in place.  It was later removed.

Tony Fishpool did a neater job.  See his work here:

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  1. If you don't want to wind your own transformer, you can find one in an H16105DF 10/100Mbps Ethernet decoupling transformer. Every ham has a junk box right? Pictures in this post ( http://eliasoenal.com/2012/11/07/rtl2832u-transformer-mod/ )

    1. Fascinating Michael. I hooked out a gigabit ethernet card from the office junkbox and the filter is a midcom 7093-37. The datasheet is online and it is similar to the filter referenced in your article. That lead me to an article with more info:
      There is some advice about adding a capacitor to the USB 5v and clamping filters around the USB cable to reduce noise. I get quite a bit from my monitor.
      I'm wondering now whether the HF performance of my dongle is not as good as it could be because I didn't remove those capacitors in order to retain VHF?

  2. Bill, the secret is a big very magnifying glass and a very small soldering iron. :-)
    de Tony G4WIF

    1. Tony: I really thought I could do it. But no. But I am glad the mod worked. Thanks for the articles in SPRAT. Bill

  3. There is even more dongle madness in the next Sprat :-)

  4. Tapping an IF should be your next next mission Bill. Welcome to RF TV :)


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