Part of our Emergency Communications and Preparedness guide.
Every prepper forum eventually gets to the same question. What happens to my radio if a nuke goes off? The honest answer is more nuanced than “everything dies,” and it depends heavily on which band you’re asking about. We actually have real world data on this, thanks to a Cold War test most hams have heard of but few have dug into. Let’s break down what Operation Starfish Prime actually showed us, and what it means for HF, VHF, and UHF specifically.
What Actually Happened at Starfish Prime
On July 9, 1962, the US detonated a 1.4 megaton warhead about 250 miles above the Pacific, roughly 900 miles from Hawaii. It was part of Operation Fishbowl, itself part of the broader Operation Dominic test series. The goal was to study exactly what we’re talking about here, high altitude nuclear effects on the electromagnetic environment.
The immediate, well documented results in Hawaii included streetlight failures, a damaged telephone company microwave link that knocked out calls between islands, and tripped burglar alarms. I’ll flag something for accuracy’s sake here though. A later reanalysis (Vittitoe’s arxiv paper, if you want to go read it yourself) found that the “hundreds of streetlights” story gets exaggerated in a lot of retellings. Out of more than 10,000 streetlights on Oahu, only 10 to 30 fuses actually tripped, and Hawaiian telephone, radio, and TV broadcasts kept running. The event was real and the pulse was bigger than scientists expected, but it wasn’t a total blackout of every electronic device on the islands. I mention this because a lot of prepper content overstates Starfish Prime for dramatic effect, and I’d rather give you the accurate picture.
What’s not disputed is the damage in orbit. The pulse pumped a huge number of high energy electrons into the Van Allen belts, and that artificial radiation ended up killing at least six satellites over the following months, including Telstar 1.
Three Different Problems, Not One Big Zap
A high altitude nuclear EMP isn’t a single event. Physicists break it into three phases, and each one hits your radio gear differently.
E1 is the fast component, a nanosecond scale pulse driven by gamma rays knocking electrons loose in the upper atmosphere. This is the part that induces huge transient voltages in anything acting like an antenna, wiring, printed circuit traces, feedlines. It’s what fries unprotected semiconductors. E2 follows right behind and behaves more like the pulse from a lightning strike, something ham radio gear is already somewhat hardened against if you’ve got proper grounding and surge protection. E3 is the slow one, lasting seconds to minutes, and it’s a geomagnetic effect that induces current in very long conductors: power lines, pipelines, and telephone trunk lines. E3 is what actually took down that Hawaiian microwave link, not a direct RF zap to a handheld sitting on someone’s dresser.
HF: The Real Casualty
Set the EMP aside for a second, because HF has a second, separate problem: the blast itself wrecks the ionosphere. A high altitude detonation ionizes the D-layer far beyond its normal daytime state, and that layer is what already absorbs HF energy during the day. Crank that ionization up and you get a radio blackout across large swaths of HF, potentially for hours to days depending on yield and altitude, entirely separate from whether your rig survived the pulse. This is the same mechanism behind the shortwave fadeouts we see after big solar flares, just far more severe and localized to the blast footprint.
So even a fully EMP-hardened HF station, sitting outside the direct pulse radius, in a Faraday enclosure, disconnected from every antenna, can come back online to find the ionosphere itself is unusable for ground wave DX and skywave propagation. NVIS and long haul HF are both at the mercy of a layer you can’t shield.
VHF and UHF: Line of Sight Survives, But
VHF and UHF are mostly line of sight and don’t rely on the ionosphere the way HF skywave does, so they’re not vulnerable to the same propagation blackout. Your handheld talking simplex to another handheld a few miles away isn’t fighting D-layer absorption.
The catch is that VHF/UHF infrastructure is exactly the kind of thing E1 and E3 love to hurt. Repeaters sitting on towers, connected to commercial power and often to landline or fiber backhaul, are vulnerable both to the fast pulse coupling into their antenna and feedline, and to the slow E3 current riding in on the power grid. A handheld in your pocket, disconnected from any long conductor, is one of the more EMP-survivable pieces of gear you own. A repeater on a hilltop with its power supply plugged into the grid is one of the least survivable. This is the same logic that shows up over and over in why you need a backup plan for when the repeater goes silent, EMP or not.
Approximate Recovery Time by Band
These numbers are rough, and I mean genuinely rough. Recovery time depends heavily on burst yield, burst altitude, your distance from ground zero, geomagnetic latitude, and time of day. Think of this as a starting mental model, not a countdown clock. All of it assumes a single Starfish Prime scale event, not a coordinated multi-burst attack, which would push the grid-dependent rows out much further.
What This Means for Your Radio Plan
A few practical takeaways I’d actually act on:
- Keep at least one handheld and one mobile radio disconnected from power and antenna, stored in a metal ammo can or similar improvised Faraday enclosure, as insurance against E1. See what’s actually worth putting in that can for a realistic, budget-honest gear list.
- Don’t assume HF comes back online just because your gear survived. Plan for a propagation blackout on top of any equipment losses, and understand that it clears on its own timeline, not yours.
- Simplex VHF/UHF between undamaged handhelds is your most likely surviving mode in the first hours, precisely because it skips both the grid-connected repeater and the wounded ionosphere.
- Don’t over-plan around a single worst case Starfish Prime style event. A regional EMP from a lower yield device, or no EMP at all, is a far more statistically likely scenario than a Cold War era megaton airburst.
Starfish Prime is a useful data point precisely because it’s real world evidence instead of a movie plot. It tells us the truth is messier than “everything electronic dies.” Some things fail immediately, some fail slowly through the power grid, and some bands go dark for reasons that have nothing to do with your equipment at all. Plan accordingly, and keep that PACE plan built around more than one band.