Saturday, August 3, 2019

Short Wave Radio After High Altitude Nuclear Explosions

I do not worry much about this.  I think North Korea is just an extortion racket on a national scale, and even if Short Fat were crazy enough to try for an EMP attack on the U.S., his commanders would recognize the glass parking lot result and probably strangle him with bare hands if needed.

But if you know any preppers with ham radio plans for such an unlikely disaster, the following may be of interest.  I am reading Glasstone's The Effects of Nuclear Weapons. In Seconds 10 54 through 10 58, he discusses the effects of high altitude nuclear explosions on HF radio.  There might be disruption of ham radio for many hours over very large areas, even if you're ham rig is adequately shielded from EMP.


  1. Yes, HF ham radio could be disrupted. VHF would probably not be, although many VHF and UHF repeaters would be knocked off the air by the E1 pulse of the H-EMP detonation, as would much of the electronics our civilization depends on.

    BTW, when Starfish Prime - the big US H-EMP test - was detonated, my father and I were listening for it on the ham radio - on the 15 or 20 meter band. My PhD Dad was an expert on the ionosphere, plus he had recently been working as a nuclear weapons designer at Sandia Base (now Sandia Labs). So, he knew when the test was going to happen.

    We didn't hear anything, although that proves nothing.

  2. As I understand it shortwave bounces its signal off the Ionosphere thus giving it over the horizon transmission capability. A nuclear blast in space can disrupt the Ionosphere and effectively prevent this bounce effect.

    Local direct-line of sight- radio and TV will not be effected by this and were not effected by the mentioned nuclear test. But during an earlier nuclear test called Teak the long range- over the horizon- radio communication between Hawaii and Johnson island was completely cut for a few hours.

  3. From what I just read, Teak was different from classic H-EMP, because it went off at too low an altitude, and thus injected fission debris into the ionosphere. Hence, the impact on the ionosphere was from both the H-EMP effect (to some extent) and these fission products, making it hard to sort out the causes.

    HF radio indeed does use the ionosphere to bounce signals beyond line of site (and beyond ground wave propagation). H-EMP will affect the ionosphere for a little while, although I am not sure what the effect will be. Also, an H-EMP detonation in space (the normal way to do it) causes a major geomagnetic storm - at the Carrington Event intensity - and that modulation of the geomagnetic field will also affect the ionosphere for awhile.

    BTW, AM radio also bounces off the ionosphere under some conditions. Long ago I worked at a 5000 watt AM station in Kansas, and we got cards from Australia as a result of occasional ionospheric propagation.

    Higher frequencies, as you say, do not rely on ionospheric propagation - or more accurately, are unable to use it - their signals go right through the ionosphere into space. The propagation for these systems is closer to line-of-sight. They will be disrupted, however, by EMP damage to the equipment, and by the loss of electric power from EMP effects - both E-1 and E-3 pulses (and to a lesser extend, E-2).