[TowerTalk] spark gaps & GDT's for lightning/static protection
Roger (K8RI) on TT
K8RI-on-TowerTalk at tm.net
Sun Apr 9 03:07:37 EDT 2017
I'm assuming this is for open wire feed line? That brings up the
question of the rig. Is it SS, or tube.
Is the tuner link coupled, or with a transformer? Is there a direct
path from the antenna "through" the tuner to the rig?
73, Roger (K8RI)
On 4/6/2017 5:35 PM, jimlux wrote:
> On 4/6/17 12:29 PM, Grant Saviers wrote:
>> I've seen pictures of all sorts of gaps, two wires almost touching,
>> interlocking rings, adjacent spheres, Jacobs ladder like rods with
>> tapered spacing , etc. One amateur radio product uses automotive spark
>> plugs (non resistor) and is sold as a pair on a copper plate for open
>> wire feeders. However, a copper plumbing sweat fitting is soldered over
>> the gap so it is impossible to measure the gap. My question is, if I
>> use a non resistor spark plug as a arc gap, is there any experience that
>> can be shared about what the gap distance should be set to? I plan to
>> have a removable cover over the gap end for WX protection .
>> Are there better designs for a gap that are easy to fabricate and
>> weather/bug resistant?
> breakdown of air is 70 kv/inch. That's in a uniform field at sea
> level, and a sparkplug or wires or whatever will breakdown at a lower
> A typical auto gap of, say, 0.030" will break down at about 1.5-2kV.
> No matter how small the gap, or how low the pressure, an air gap will
> not breakdown at less than 327 volts (the minimum sparking voltage) -
> you might get significant field emission or corona, but you won't get
> a spark.
> Argon has a much lower minimum sparking voltage - 137V
> vacuum gaps have entirely different behavior, and it's a bit of an
> arcane art to design a consistent breakdown voltage.
> The commercial transient suppression gaps might have fairly high
> parasitic C - they're basically a couple electrodes, a spacer, and a
> fill gas like neon or argon- I'd spend the $3 and measure one at your
> frequency of interest to see what the RF properties are.
> But maybe it's a few pF, and you don't care?
>> And a second question: Gas discharge capsules are used in coax
>> lightning protection devices. A large variety of gas discharge
>> components are stocked at Mouse, Digikey, etc in various voltages and
>> Kamps. Is there any difference in the RF properties of the tube in the
>> in-line coax devices vs what I can buy a lot cheaper as a component? eg
>> Littlefuse and TDK 800v @ 10Ka around $3ea.
>> Grant KZ1W
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