A Micro Dual Band Project

I’ve been toying with the idea of getting an Elecraft K1, but the price and given that I’m not comfortable with CW is a show-stopper.  I’ve also been looking for a tiny multi band kit, but the ones out there aren’t tiny enough.

Having recently just built the Radi0Kit 140  and impressed at the little rig’s receiver and small size, I came up with an idea.  Why not combine two of these into a single rig? I did this with my original Pixie (40/80) but it wasn’t a good build quality-wise.  So here is the plan.  It’s not going to be an Elecraft K1, but it will be about 1/10th the price and be dual band, and it will be about 3x3x2″.

Step 1: Get the kits (I got a 40 and 20m kit off of eBay.  They ship from Greece, so I’m calling my little rig the ß (beta as in 2).


Radi0Kit 140 and 120 (40m, 20m)

Step 2: Get a case of minimal size with some “head room” for connectors and such.  I got a 3x3x2 enclosure from http://polycase.com.

Polycase enclosure

Polycase enclosure

Step 3: Mark the mounting holes in the case prior to building the kits (yes, I’ve done it the other way. Ugh.)

Step 4: What do I want to add? I’m going to try to incorporate the Hendrick’s Tayloe SWR Indicator and Bridge. I have one lying around I built a while back. I’ll pull it from its aluminum frame and that will give me a board that is approximately  1-3/4″ x 1″ x 3/4″. I also want to include a small BCI filter on the output which I can build on a tiny PCB or perfboard.  A power LED would be good and I’ll use a DPST center off switch to switch bands and power.  I’ll isolate the boards/bands with a few diodes.  I could include a small audio amp/speaker but that would be pushing my abilities to cram things neatly.  Likewise, a 9v battery would work, but I’ll just add a power connection so I can run off of batteries or plug it in.  So now we have to fit:

  • 2 PCB boards in a stack.
  • 1 SWR Indicator / Bridge board.
  • 1 DPST center off band/power switch.
  • 2 LEDs (power and the one that comes with the SWR I/B.
  • 1 BCI filter board
  • 1 audio jack for headphones
  • 1 key jack
  • 1 BNC antenna connector
  • 1 power connector

Step 5: Brainstorm an initial case layout (Close to scale, but not exact).  The SWR I/B and BCI boards will be mounted on-edge. The Radi0Kit boards are just a fraction of an inch too tall to fit on-edge.

Preliminary layout

Preliminary layout

Step 6: The main switching circuit. I’ve been looking into doing multi-band Rockmites, and in my stash of materials, I came across a nice build on N5ESE’s website.  He has a nice circuit diagram that switch the power, antenna, key, keyer and headphone jacks.  This is basically my plan.  I’ve “stolen” his diagram and reworked it, basically eliminating the keyer circuit that exists in the Rockmite, but not in the Radi0Kit.  I’m crediting N5ESE for this design (see his site for the original).

Modified N5ESE dual-band Rockmite circuit.

Modified N5ESE dual-band Rockmite circuit.

Now the real work begins…


About Archimage

I'm an expert in massively distributed fault-tolerant systems. I'm also an iOS developer, blogger, beer brewer, and I have been told I'm a nice guy.
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