[TowerTalk] spark gaps & GDT's for lightning/static protection

[Roger (K8RI) on TT]

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 
> level.
>
> 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.
>>
>> http://www.littelfuse.com/~/media/electronics/datasheets/gas_discharge_tubes/littelfuse_gdt_cg_cg2_datasheet.pdf.pdf 
>>
>>
>>
>> Grant KZ1W
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>>
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-- 

73

Roger (K8RI)


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