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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