This is the project that best explains why I got into ham radio in the first place: not to talk, but to build. It’s a complete, field-deployable HF station bolted into a ten-inch 3D-printed rack, powered off a cordless-drill battery, and carried into the woods for POTA. Every module in it is something I wanted to understand from the inside out — so I put them all in one box and wired them together.

I built it with WD4PVS, who did the CAD work: modeling the rack mounts and dialing in the fitment for every module so the whole thing actually bolts together like real gear instead of a pile of boards zip-tied to a project box.

Why a rack?

Portable HF usually means a radio, a tangle of pigtails, a battery, and a tuner all rattling around loose in a bag. It works, but it’s fragile and it’s slow to set up. I wanted a station where the signal chain was fixed — every module in its place, every interconnect short and strain-relieved — so deployment is “clamp the battery on and raise the antenna,” not “reverse-engineer last week’s wiring.”

The answer was a 10-inch mini rack. The frame is 3D-printed from the LabRax system — a set of open, printable rack parts sized for the small “10-inch” standard rather than a full 19-inch data-center rack. That’s the sweet spot for ham gear: big enough to hold real modules on faceplates, small enough to carry with one hand.

WD4PVS took each module and modeled a mount and faceplate for it, so the QRP radio, the amplifier, the meter, the filters, the tuner, and the Pi all sit on their own rack unit. Printed plastic is perfect here — every module has a different footprint, and CAD-and-print lets you make a custom bracket for each one in an afternoon instead of hunting for aluminum that almost fits.

The signal chain

Here’s the path a signal takes from the radio to the antenna, which is also the order the modules stack in the rack:

SDX+ V2 → 35W amplifier → low-pass filter → SWR meter → ATU-100 tuner → antenna

SDX+ V2 — the heart of it

The SDX+ V2 is the QRP HF transceiver at the center of the station. It’s a kit-lineage radio — small, efficient, and exactly the kind of thing an edge-case ham loves, because you can actually see and understand what every stage does. Running QRP (low power) is a feature, not a limitation: it’s what lets the whole station sip from a tool battery.

35W amplifier

QRP is elegant, but sometimes you need the extra few S-units to make the contact, especially on a crowded POTA activation. A 35W amplifier brings the SDX+’s QRP output up to a level that punches through without turning the station into a power hog.

Low-pass filter + Pi Pico band selector

Any time you amplify, you have to deal with harmonics — spurious energy at multiples of your operating frequency that you are legally and neighborly obliged not to transmit. That’s what the low-pass filter is for: it passes your band and attenuates the harmonics above it.

The clever part is the Pi Pico low-pass-filter selector, built from Tech Minds’ design. Instead of one fixed filter, a Raspberry Pi Pico switches the correct LPF for whatever band I’m on — automatic harmonic filtering that follows the radio. It’s a tiny microcontroller doing exactly one job well, which is my favorite kind of homebrew.

SWR meter and the ATU-100 tuner

A rack-mounted SWR meter gives me a constant read on how well power is actually getting into the antenna versus reflecting back at the radio. Feeding it is the ATU-100 — an automatic antenna tuner (not an antenna; the name trips people up). It’s an autotuner that matches whatever wire I’ve thrown into a tree to something the radio is happy driving, and it does it in a second or two at the press of a button. In the field, where your “antenna” is whatever you could hang between two trees, an autotuner is the difference between operating and packing up.

The digital side: AIOC and a Raspberry Pi 5

Voice and CW are only half of modern ham radio. For the digital modes — FT8 and the rest — I bring the station into the computer age with an AIOC (All-In-One-Cable), a tiny USB interface that handles the radio’s audio and PTT without a rat’s nest of sound-card adapters.

The AIOC feeds a Raspberry Pi 5 running the digital-mode software, with a 7-inch touchscreen as the control surface. No laptop required — the whole computing side of the station is a rack module too. Tap to decode, tap to call.

Powered by a drill battery

Here’s the detail that makes people grin at hamfests: the entire station runs off an 18V Milwaukee M18 battery — the same pack that runs my power tools. It’s rugged, it’s already in my kit, and swapping a dead one for a fresh one takes three seconds. For POTA and emergency work, standardizing on a battery ecosystem I already own means one less thing to think about and one less special charger to forget.

In the field

Built for two jobs: POTA (Parks On The Air) activations, and emergency communications when the grid isn’t there to help. Both want the same things — fast setup, no mains power, and a station rugged enough to survive a backpack and a tailgate. The rack delivers on all three.

I’ll follow up with real field numbers — power out, SWR across bands, battery runtime on a single M18 — once I’ve logged a few more activations. If you’re building something similar, or you want the print files and mounting details from WD4PVS’s models, get in touch.

73, W3MRB