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Tag: SDR

Software Defined Radios and circuitry

  • Ham It Up Noise Source Enable Switch

    Some rummaging produced a tiny DPDT switch that actually fit the holes intended for a pin header on the recently arrived Ham It Up board, at least after I amputated 2/3 of the poor thing’s legs:

    Ham-It-Up - noise source switch - B
    Ham-It-Up – noise source switch – B

    The new SMA noise output jack sits in the front left, with the white “noise on” LED just left of the switch:

    Ham-It-Up - noise source switch - A
    Ham-It-Up – noise source switch – A

    There’s no way to measure these things accurately, at least as far as I can tell, but the holes came out pretty close to where they should be. The new SMA connector lined up horizontally with the existing IF output jack and vertically with the measured / rounded-to-the-nearest-millimeter on-center distance:

    Ham It Up - noise SMA drilling
    Ham It Up – noise SMA drilling

    The Enable switch doesn’t quite line up with the LED, so the holes will always look like I screwed up:

    Ham-It-Up - noise source switch - case holes
    Ham-It-Up – noise source switch – case holes

    That’s OK, nobody will ever notice.

    Now, to stack up enough adapters to get from the SMA on the Ham It Up board to the N connector on the spectrum analyzer …

     

  • Ham It Up Noise Source

    An RTL-SDR receiver & Ham It Up RF upconverter arrived, with the intent of poking at LF signals. The upconverter circuit board also contains a mostly populated RF noise source:

    Ham-It-Up v1.3 noise source - schematic
    Ham-It-Up v1.3 noise source – schematic

    Being a sucker for noise sources, I spent some time pondering the circuitry.

    The as-built board has a 0 Ω jumper instead of the 6 dB pad along the upper right edge:

    Ham-It-Up v1.3 - noise components
    Ham-It-Up v1.3 – noise components

    The previous version had a pi bandpass filter in place of the pad and you could certainly repopulate it with two caps and a teeny inductor if you so desired.

    I added the SMA connector, which isn’t quite identical to the IF output connector above it:

    Ham-It-Up v1.3 - noise SMA
    Ham-It-Up v1.3 – noise SMA

    That will require a new hole in the end plate that I’ll get around to shortly. It also needs an external switch connected to the Enable jumper, but that’s in the nature of fine tuning.

    I’m awaiting a handful of adapters & cables from halfway around the planet…