I run an ADS-B receiver at home — it decodes the transponder broadcasts from aircraft overhead, plots them on a live map, and feeds the data to FlightAware. It started life the lazy way: an RTL-SDR dongle plugged into a server indoors, with a run of coax to an antenna. That works, but it’s the wrong topology if you want range, and I wanted to move the whole thing up high and outdoors.

Two things came out of that project worth writing down. First, a diagnostic detour that taught me the map wasn’t lying to me even though it looked like it was. Second — the real content — how to relocate an SDR receiver to the top of a mast without breaking MLAT, which is the part most “just put a Pi outside” guides skip.

Aiming an over-the-air TV antenna is traditionally a two-person job with a lot of yelling: one person on the roof rotating the mast, one inside shouting “better… worse… BETTER… no, worse again.” The feedback loop is slow, the signal bar in the tuner’s web UI updates lazily, and you can never quite tell whether that last nudge helped.

I wanted a tight feedback loop: a live graph, updating every few seconds, of the exact signal metrics that matter — so I could rotate the antenna and watch a line move in real time. My tuner is an HDHomeRun FLEX 4K, and it turns out you can scrape per-tuner signal quality straight into Prometheus and chart it in Grafana. This post is how I built that, the one exporter that actually does the job, and the surprise ending where the data explained a “broken” channel that wasn’t broken at all.

I opened my Frigate dashboard one morning and my stomach dropped: 0 detections, hundreds of alerts. My first read was the obvious one — the object detector had fallen over, and Frigate was now firing blind, alerting on raw motion instead of actual objects.

That read was completely wrong. Nothing had broken. The detector was healthy, running OpenVINO inference at ~10 ms per frame the entire time. What had actually happened is that I didn’t understand what the words “Alert” and “Detection” mean in modern Frigate — and once I did, the “outage” evaporated and turned into a five-minute config change.

This is a post about a debugging story with a satisfying anticlimax, and about a genuinely confusing bit of Frigate’s UI vocabulary that trips up a lot of people running 0.14 and later.