Kiwi + Lightning

Yesterday we had a strong thunderstorm about 20-30 km away from me.
I was curious how much voltage I would have on the antenna input and attached an oscilloscope. A few times per minute I had spikes above 5V, every 10 minutes or so above 10V and few were off the scale (>50V).

Would that be harmful for the kiwi? In the schematic I've seen 3.3V TVS diodes on the input. If i remember correctly, they can become low impedance, when they're triggered too often, is that correct?
On the other hand there is a nearby kiwi that is on 24/7, even in the strongest thunderstorms and it still works.


  • With a TVS it's not so much the voltage that kills them as the time profile of the current pulse. The Kiwi uses the CDSOD323-T03C and the data sheet is here:
  • That reminds me of this video I shot of an LED connected to one of my antennas during a thunderstorm (sorry for the poor quality)
  • Chris,
    Nice video. I enjoyed seeing it. It's probably a question of total energy delivered to the diodes, as John suggested.
    From a somewhat broader perspective, I think that lightning noise is actually what we all hope to hear with our Kiwis. This because the propagated noise floor is essentially that from world-wide lightning strikes, at least at most places up to near 30 MHz where perhaps galactic noise eventually exceeds it.
    Funny, in a way we are trying to optimize the dynamic range of a kiwi system such that it can hear weak lightning while it doesn't get toasted by the strong stuff!
  • I wonder what type of antenna you're using...
  • Haha I've tried it and the LED flashes too at my antenna! Not as hefty as yours though, but the storm is pretty far away.
    I have an endfed wire, 20m long and 6m above ground.
  • If you put a balun or unun on the input to the kiwi, a type that has a DC ground, I would think you'd get some protection.
  • In my case it is actually worse with a 9:1 unun. Apparently it converts high impedance lightning energy to low impedance LED energy :smiley:
    Could read a newspaper with that LED flashing.
  • does your UNUN have a path to ground for the "hot" wire? Not all do
  • Yes, i made it myself.
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