Roger (K8RI) wrote:
>
>
> On 9/13/2010 8:58 PM, jimlux wrote:
>> Gary Schafer wrote:
>>> Simple spark gaps are not so simple. Temperature, humidity,
>>> contamination by
>>> dirt etc will all make a difference on what voltage they arc at. Gas
>>> tubes
>>> are much simpler and more reliable for repeatability of breakdown
>>> voltage.
>>
>> Indeed, gas tubes are nice for that reason, BUT.. they do cost more
>> than a couple pieces of wire (not much more), and I'm not sure that in
>> this application you need that kind of control. After all, the
>> original intent here was for installation at the tower, *in addition
>> to* the high quality protection at the shack entrance. All you're
>> really doing here is protecting the relatively cheap relay, or, more
>> accurately, saving yourself the hassle of replacing it on a big strike.
>>
>> And, the breakdown voltage doesn't change all that much. It goes as
>> density of the air, so from -20C to +50C, you're talking about 20%
>> variation or so. Humidity effect is very small.. maybe a couple percent.
>>
> The problem from humidity comes from condensation and that condensation
> is far from pure, just check the PH. It'll conduct like crazy and with
> a .020 to .030" gap it's likely to bridge the gap creating a conductive
> path. OTOH after a slight burp in the impedance at a KW it'll
> clear...or initiate an arc.
wouldn't that same condensation also bridge the relay contacts?
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