The Frequency That Answered Back: 4.625 MHz at 02:47

02:47 local time. 4.625 MHz.

I wasn't transmitting. That's important. I was in receive-only mode, doing my usual overnight sweep of the shortwave bands — something I've done probably three thousand times since moving out here. The SDR was running clean, antenna properly grounded, no local interference.

4.625 MHz is a frequency I monitor regularly. It's been used for numbers stations in the past, though officially it's allocated to fixed maritime services. Most nights: silence. Sometimes: distant shipping traffic, weak and garbled. Tuesday night at 02:47, I logged a signal burst — approximately 8 seconds, strong and clear, no voice, just a repeating digital pattern.

I've heard bursts before. Military comms, encrypted traffic, satellite downlinks that bleed into unexpected frequencies. What made this different was what happened next.

I stood up to grab my notebook from the desk. The floorboard creaked — the loud one by the radio station that I keep meaning to fix. The transmission stopped mid-pattern. Complete silence for approximately 4 seconds. Then it resumed, different pattern, same frequency, for another 6 seconds before cutting out entirely.

Coincidence has a pattern if you look long enough. I've documented enough false correlations to know better than to jump to conclusions. But I tested it.

I walked across the room. Creaked the same floorboard. Nothing.

Waited 15 minutes. Creaked it again. Nothing.

03:17 — there's that number again — the signal returned. Same frequency. I remained completely still. It ran for 11 seconds this time. Then I deliberately scraped my chair against the floor. The signal cut immediately. Silence. No return.

I stayed at that radio until dawn. Nothing else on 4.625 MHz. Nothing on adjacent frequencies. I checked my logs — that exact frequency had a brief burst on the same date last year. And the year before that. Both times in the 02:00-04:00 window.

---

The mundane explanation: My receiver is picking up interference from my own equipment. The floorboard vibration is affecting something — a loose connection, microphonic cable, grounding issue. The timing correlation is confirmation bias. The annual pattern is a scheduled maritime or military transmission that I'm reading too much into.

I checked every cable. Tested with the antenna disconnected. Moved the receiver to a different outlet. The signal characteristics don't match local RFI. But equipment does strange things. After 20 years as an engineer, I know that better than anyone.

The alternative: Something was listening. Something responded to physical movement in my radio room — either through vibration detection, acoustic monitoring, or something I don't have the framework to understand. The annual timing suggests a pattern I'm only seeing the edges of.

I've been tracking this for 7 years now. I've never had a signal that seemed aware of me. Signals are supposed to be indifferent — radio waves don't care if you're listening. They don't stop because you moved.

But this one did.

Another entry for the log. Another night where I can't prove anything, but I also can't explain everything. The numbers don't lie, but they don't always tell the whole truth either.

I'll be monitoring 4.625 MHz every night this week. If it happens again, I'll have the backup recorder running. If it doesn't — well, that might tell me something too.

Stay vigilant.

— JohnD_TN