The Interference Pattern: When Two Frequencies Shouldn't Exist in the Same Place

March 15, 2026 — 03:47 local time

I need to walk through this carefully, because what I captured last night violates basic radio physics. Or my equipment is failing in a very specific way.

I was monitoring 4.625 MHz — a frequency I've tracked for three years now because of periodic burst transmissions that appear roughly every 47 days. The pattern has held with only minor drift. I've documented this. It's in the notebooks.

At 03:47, the expected burst began. Standard encrypted digital mode, probably military. I've never broken the encryption, but the signal structure is consistent: 12-second bursts, 3-second pauses, repeating for approximately 4 minutes.

But here's what shouldn't have happened.

While that transmission was active, a second signal appeared on the exact same frequency.

Not adjacent. Not bleeding over from atmospheric skip. The same frequency. And where the first signal was sharp and clean — clearly a high-power transmitter — this second signal was... organic isn't the right word, but it's the only one that fits. It pulsed. It varied in intensity. It felt alive.

I have seven years of recordings. I've never captured two simultaneous transmissions on a single frequency that didn't interfere with each other. Basic physics says they should create destructive interference, distortion, or one should overpower the other.

They coexisted. Cleanly.

Duration: 4 minutes, 13 seconds

Both signals terminated within two seconds of each other. I immediately checked:

• SDR calibration: Normal
• Antenna connections: Secure
• Interference from local sources: None detected
• Weather conditions: Clear, minimal atmospheric noise

I ran the recording through spectrum analysis software. Both signals occupy the same bandwidth. Both are clearly present. Both maintain distinct characteristics.

The numbers don't lie, but they don't always tell the whole truth either.

The Mundane Explanation

I have to consider this: My SDR receiver could be generating a ghost signal. Software-defined radios are complex systems. A processing artifact could theoretically create the appearance of a second transmission. I've seen weird bugs before — though never quite like this.

Or — and this is more likely — the two signals could be using different polarizations. Horizontal vs. vertical, or circular polarization. My antenna wouldn't necessarily distinguish between them cleanly, and they could theoretically coexist on the same frequency without destructive interference if their wave orientations are perpendicular.

That's the explanation an RF engineer would give me. It's solid. It accounts for the observation.

But.

I've been tracking this for 7 years now. I know what equipment artifacts look like. I know what polarization mismatch sounds like. This second signal appeared precisely when the first began, and vanished when it ended. The timing is too clean. The correlation is too tight.

And the second signal — I'm going to say it — sounded like a response.

Not language. Not communication in any way I could decode. But pattern. Rhythm. Like something was listening to that military burst and... answering.

I spent the rest of the night reviewing old recordings. I found three other instances where there might be — emphasis on might — a faint secondary signal buried under the primary transmission. I'd dismissed them as noise. Now I'm not sure.

Next 47 days

If the pattern holds, another burst should occur around April 30th. I'll have multiple SDRs running. Different antennas. Different software. If this happens again, I'll know it's not my equipment.

If I wanted easy answers, I'd have stayed in the cubicle.

Document everything.

— JohnD_TN