This is an interesting question..... Whether having one or more beam elements
insulated from the boom causes increased precipitation static in the typical
Yagi-Uda is not clear to me.... We are dealing with two electromagnetic
phenomena here.. one is DC static charge, which is easily drained to the
tower/coax-braid and carried to ground....and the other is precipitation
induced, RF noise (precip static), which is more problematical....
We know that a long wire antenna, using bare wire, is subject to a DC static
charge build up, from drops of water/snow/dust (and even dry wind blowing
across the wire) carrying an electrons with them as they depart.... This is
well known to anyone who has touched said wire, causing the capacitive charge
to dissipate through his fingers...
As a 12 year old I was helping my Dad and Gramps put new fencing around our
farm... Gramps said, "Hand me the end of that wire", and I grabbed onto one
end of a mile of that brand new electric fence, right after a rain shower,
and I'm here to tell ya', it was shocking......
Using insulated wire significantly reduces static charge build up (and the RF
popping noise that happens with each droplet departure)... and most
transceivers have an RF choke to ground at the antenna connector, which
should drain static charge currents as they occur, not allowing the DC
voltage to build up.......
Now, on to beams....
Assuming the tower is grounded, then the top of the tower is a DC ground,
with some series resistance, but it is not an RF ground by any stretch of
the imagination... esp. at the frequencies at which is an odd # of quarter
waves tall...
Grounding the center of the elements to the boom (plumbers delight
construction) has two deleterious side effects, in my opinion... First, is
that it allows unbalanced RFcurrents to flow on the boom, degrading that
pristine antenna pattern I paid for (esp. the F/S ratio).... Secondly, it
couples all the vertically polarized RF noise picked up by the tower,
directly into the horizontally polarized (and theoretically quieter) beam
antenna, causing the receiver to hear more noise.... If I wanted to listen to
noise, I would have saved money and bought a Butternut, et. al. , vertical
in the first place...
I can see no harm in using an RF choke to DC ground the center of the antenna
elements to the boom... this will prevent a static charge build up... but, I
doubt that it will tame the RF static, from the droplets departing the
_driven_ element... I paint my beams with polyurethane exterior varnish for
two reasons... to insulate the element and reduce the precip static... and to
preserve the shine....
The other question is whether precip static on the non-driven and ungrounded
elements of the Yagi-Uda beam is radiated to the driven element (and carried
to the receiver) ?.... I suggest that experimentation is in order... Someone
with the the time and energy could install relays at the element centers so
that they can be... grounded to the boom V/S left insulated V/S grounded
through an RF choke... and make noise measurements... Should make a good
article for the magazines, and be interesting, to boot...
Cheers ... Denny k8do@aol.com
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