[TowerTalk] DC grounding of parasitic eles with insulators ?

[K9MA]

Does anyone know of a modern NEC-designed yagi that does NOT use 
isolated elements? Perhaps there is some software that can accurately 
model the effect of the boom, but I suspect it's way out of the price 
range of the designers of amateur antennas. I know NEC4 is better than 
NEC3, but still has problems with very closely spaced wires.

I'd expect the water to pretty effectively bleed off rain static, but I 
don't know about snow. This will be my first winter with isolated elements.

73,
Scott K9MA

On 10/28/2019 13:58, john at kk9a.com wrote:
> Like most modern day contest stations, I built my Yagis with insulated 
> elements and direct feed. According to W8JI's site, grounding the 
> elements makes little difference in precipitation static. 
> https://www.w8ji.com/pecipitation_static.htm  I have not seen any 
> issues using them and as a plus it makes modeling easier.
>
>
> John KK9A
>
>
> K9MA wrote:
>
> The reason the parasitic elements are isolated from the boom is that the
> boom would detune them. AFAIK, no one has figured out a way to model
> elements shorted to a boom, and experimentally tuning an antenna is
> expensive.
>
> I can think of 3 reasons to connect the elements to the boom:
>
> 1. Bleed rain/snow static
> 2. Protect the insulators in case of a nearby lightning strike
> 3. Protect the DE balun when the tower is shunt fed
>
> A 1 megohm resistor would take care of number 1. An RF choke might take
> care of number 2 without detuning the parasitics.  If you shunt feed the
> tower and don't have something like a hairpin match on the DE, a choke
> ala N9NB's recent QST article is required. (This is sort of the opposite
> of a common mode choke.)
>
> That said, i recently put up a JK Mid-Tri, which has all the elements
> isolated. Since I shunt feed the tower, I put the N9NB choke on the
> driven elements. (And the same on the D40 above the beam.) I didn't
> think of putting the bleed resistors on the parasitics. I don't think
> rain will be a problem, but we'll see about snow static. If a lightning
> strike blows up some insulators, I'll probably have bigger problems.
>
> 73,
> Scott K9MA
>
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-- 
Scott  K9MA

k9ma at sdellington.us