Help wanted for new project… The Big Box O’ RF

April 29, 2015 | Amateur Radio | By: Mark VandeWettering

As I’ve mentioned over the last few months, I have piles of different development boards, and lots of little display modules and the like. I’ve been thinking of doing a simple radio project, aimed at helping further experimentation with QRP (low-power) radio homebrewing. Inspired by Pete and Bill over at the Soldersmoke Podcast, I thought that I might use a dev board to build a gadget which I am calling:

The Big Box O’ RF

The idea is to take an Arduino (or maybe Teensy?), and connect a couple of different peripherals to it that can generate RF. I have both an AD9850 DDS module:


And one of Adafruit’s Si5351 boards, which are cool because they can generate three different outputs at once, under I2C control:


I also have one of Jason’s (NT7S) little Si5351 kits that I could assemble:


And of course I have a bunch of I2C display peripherals, some rotary encoders, and various power jacks. All I really need would be a nice aluminum box, and I could assemble a general purpose signal source/VFO that I could use in experiments.

Sounds pretty cool, yes?

Well, I have a few details to work out:

  • I’m envisioning a front panel which has a bunch of panel mount connectors that I can attach coax pigtails to route RF to my various project. (Probably 4, one for the AD9850, and three for outputs from the Si5351). The (semi) obvious choice would be SMA female panel connectors, and use pigtails to inject the RF into various other projects. Does anyone have any recommendations for where to get reasonably inexpensive SMA male-male pigtails? Is there a better (read cheaper) alternative that could be used? I’ve used Type F or even RCA jacks before, is that stupid?
  • Inside the box, would you use RG174 or RG316 to carry RF signals from the board outputs to the panel mounts? Any hints on shielding?
  • Should I make a buffer amplifier for the outputs? Or low pass filter modules (switchable?)

This project doesn’t need to be perfect, but it would be nice if it was good enough to serve as test equipment that I would want to keep on my desk. Anybody have any ideas?

Addendum: This box built by Bob, WV2YAU seems close to what I have in mind: