Tuning the Dengus handheld's 915MHz antenna

The Dengus handheld has a 915MHz radio in it, and a radio is only as good as the antenna matching behind it. So the antenna got tuned.

The tool for the job is a NanoVNA, the cheap little vector network analyser that put this kind of work within everyone's reach. Solder a pigtail onto the antenna feed, sweep the band, and watch where the match lands on the Smith chart.

It never lands where the datasheet promised. An antenna is tuned by everything around it: the ground plane, the enclosure plastics, the battery, the hand holding it. The fix is the matching network, a few passives between the radio and the antenna, swapped one value at a time until the impedance pulls in to 50 ohms where you need it.

A few rounds of change a part, re-sweep, squint at the chart, and the Dengus was matched at 915MHz. Not glamorous work, but it's the difference between a radio that reaches and one that doesn't.