Subject: Re: Topband: Covered /bare antennn wire
As you have said it is difficult to get a A-B test unless instant
switching or direct observation is available.
The purpose of my test was to see if p-static was caused by individual
charged particles as they hit the wire, or some other mechanism like
corona discharge into the charged air or charged cloud of particles.
My thought was if it was charged particles each making noise, the pitch or
frequency distribution would be at the rate of particle contact, and that
insulation should mute the effect by slowing rise time of charge transfer
from particles to the wire.
Clearly the noise was all from corona at sharp points.
This also agrees with the effects people with multiple antennas see, or
even two-way antenna on tall buildings or towers. The highest and most
protruding antenna has the first and worse noise. Grounded elements,
fiberglass housings, and other tricks make no difference at all. The only
thing that matters is streamers from the exact point of corona leakage.
We saw this when a repeater moved from side mount on a tower to a building
roof peak. The fiberglass Station Master was swapped for a grounded folded
dipole antenna, and both were equally useless in bad weather. The only
thing that improved p-static noise was using an antenna well below the
height of other sticks on the roof, but that didn't work out because of
severe pattern nulls. We could raise the antenna and watch the noise
increase, and at the same time actually hear the same sizzling
acoustically through our ears and see it at night from antenna tips.
Everyone with stacked monoband identical Yagis sees this on the top
antenna. The top antenna is always terrible in inclement weather, even
though the same precipitation strikes all antennas equally and the
antennas are all on the same tower.
This all, since it all always agrees, clearly means the noise has nothing
to do with static drain or insulated or bare conductors. It is all about
where the highest voltage gradient to space around the antenna is, and how
easy that point can "leak" (generate corona).
I was hoping for a test something like, side by side identical wires, one
insulated, and one un-insulated with voltage measuring devices at the
ends.
Also separated enough not to get Beverage coupling, and using real stormy
weather measuring.
Over the insulation breakdown voltage, one would expect them to be equal
anyway.
Leakage current to earth was identical in my spray tests. It has nothing
to do with insulation breakdown. It is more like the effect of a charged
plastic comb. The charge obviously distributed right through the
insulation. I suppose if the insulation was really thick the charge
migration would be pretty slow, but charging of the wire is not what makes
the noise we are concerned with. The noise comes from corona.
I've had insulated wire Beverages and bare wire Beverages since the 1960's
or 1970's, often at the same time as mixtures of wire. Neither is any
quieter for me for local storm static.
My bare wire Beverages here are dead quiet even while Yagi's are useless
in foul weather, unless the Beverage points at the towers or are near tall
trees.
73 Tom
_______________________________________________
Topband reflector - topband@contesting.com
Before I moved here in 89 I had a KLM 4el 40M yagi at 120' that was very
noisy during blowing snow and less in the rain. All elements were insulated
from the boom.
When I moved here (same town, 500' higher) the tower was initally 160'. I
grounded the reflector and director centers to the boom using wide AL strap
per KLM's suggestion. The dual driven elements then had low inductance heavy
wire, very low DC resistance, chokes added (my own idea based upon what the
USN did for receiver static) to each phasing line at the feed end and to the
boom.
There was nothing above it most of the time and those were a short
experiment with a 20' boom 4el 10M (too high based upon 2 contests compared
to the switchable 4 high stack) and a 34' boom 6el 6M (about 6 months)
during the tail end of a sun spot cycle that did wonders on weak F2
openings.
Another thing I did with that KLM at the new QTH was to toss their 4:1
voltage balun (it started acting up just before I moved) and build one from
a 1/2 wave of coax and then added a big coax choke at the feed connector.
All the changes were done at the same time so Ive no idea if any particular
step did the trick or if it was cumulative.
No more P-static as shown in the 40M scores in various all band contests.
The 4 stacked 20M monobanders on the same tower below the 40 were silent as
were the 10 and 15M stacks on other towers that had various VHF/UHF long
yagis above them. Ive no idea if they helped or not.
I would suggest trying various methods on 160 or other bands as the jury is
still out on what works, when, where, and how.
Carl
KM1H
_______________________________________________
Topband reflector - topband@contesting.com
|