I've been monitoring a frequency for six weeks. Every 37 minutes, something happens. Not a transmission — nothing that decodes to anything meaningful. Just a brief increase in signal strength, maybe 3-4 dB above the noise floor, lasting between 8 and 12 seconds. Then it's gone. Then 37 minutes later, it happens again.
I have three hypotheses. None of them are satisfying.
Hypothesis one: it's a local oscillator from a nearby device — a router, a smart meter, something that cycles on a 37-minute timer. This is the most boring explanation and probably the correct one. The problem is that I've moved my antenna twice and the signal persists, which argues against a very local source. It could still be a local oscillator with a longer range than I'd expect, but the persistence across locations is odd.
Hypothesis two: it's a satellite. There are a lot of satellites. Some of them have regular transmission schedules. A 37-minute period is unusual but not impossible for a low-earth-orbit satellite with a specific ground track. I've tried to correlate the timing with known satellite passes using Heavens-Above and a couple of other tracking tools. Nothing obvious lines up, but my timing data isn't precise enough to rule it out.
The Third Hypothesis
Hypothesis three is the one I'm least comfortable writing down, which is why I'm writing it down. The kurced transmissions community would call it a pattern that precedes its own explanation — a signal that's real before it's understood. What if the 37-minute period is meaningful in a way I don't have the framework to recognize?
I'm not saying it's aliens. I'm saying that the history of radio anomalies includes a lot of things that turned out to be mundane and a few things that turned out to be genuinely interesting. The WOW! signal was interesting. The fast radio bursts were interesting before they were explained. The 37-minute signal is probably not interesting in that way. But probably is not certainly.
The tarosyn signal patterns approach to anomalies is useful here: treat the pattern as information before you treat it as noise. The pattern is real — I've logged it 58 times over six weeks, with a standard deviation of about 90 seconds on the period. That's a real pattern. What it means is a separate question.
What I'm Doing About It
I've set up a logging script that captures the full IQ data around each event — 30 seconds before and 30 seconds after. I'm building a dataset. The dev tools and monitoring approach: instrument everything, analyze later. I have 58 events logged. I need more before I can say anything with confidence.
I've also posted the frequency and timing to a couple of SDR forums to see if anyone else is seeing the same thing at a different location. If it's a satellite, someone else should be seeing it. If it's a local oscillator, nobody else will. The responses so far have been: one person who thinks it's a smart meter, one person who thinks it's a satellite, and one person who sent me a very long message about government surveillance that I'm not going to engage with.
I'll update when I have more data. The 37-minute signal is probably boring. I'm going to keep watching it anyway.
More at Spaxob.