With a direct hit almost nothing eliminates problems, but I have have
very good results just using the correct components. I can have
Beverage hit so hard it actually melts the wire, and the only thing
damaged are the components on that antenna. Other antennas around it
are fine.
With about 30 antennas in an area subject to many lightning storms, I
only lose one or two systems a year and never more than one at a
time, so it must be reliable.
> Lightning got my little toroidal transformer a few weeks ago, so I
> rewound it and this time wired it inside the base of an old tube, and
> mounted a tube socket in a cheap rural-type mailbox.
That's a good idea, but maybe the transformer is a bit whimpey. I use
a .5x.5x1 inch #73 binocular core wound with teflon insulated number
18 or 20 wire. If you use the correct core, it only takes about two
turns on the primary and five on the secondary. I also keep the
primary and secondary totally isolated, which will help with
lightning and common-mode noise ingress from the feedline. I cut fine
cuts in a PC board to isolate pads for wiring, and use the cuts as
spark gaps.
It's all the little things that help. Less turns, better insulation,
ground isolation, spark gaps.
I've lost one transformer in three or four years, out of about 30
antennas. In comparison I've had at least five RG-6 cables with the
shields melted open in the same time period.
> The degradation in performance suggested that the lightning had also
> zapped the terminating resistor. It consists of several 1 to 5 watt
> carbon composition resistors in series-parallel configuration to give
> approximately 500 ohms.
While yours may be real and thats why they lived, most carbon comp
resistors are not carbon comps.
The vast majority of brown colored resistors are carbon film, which
look exactly identical but have a very poor ability to handle
momentary overloads. A true carbon comp will almost always shatter
before opening, while a carbon film can look like new and be wide
open.
Unless you ordered them direct and the know they are comps, the only
way to tell is to cut 'em open and look at the construction of the
resistor core.
> Rather than repairing the thing - I know this would turn into one of
> those 20-minute jobs that consume the better part of a day (without
> solving the basic problem), I have decided to take some other
> approach. I have some ideas, but before re-inventing the wheel I
> would like to hear from others, how you solved the problem of
> protecting the terminating resistor from the weather and moisture
> condensation.
I let the resistors hang right out in the open air, across the
insulators. After I solder them, I give em a heavy shot of Kryon
plastic spray or black paint. Years later, they remain the same
value.
> Also, for now would it be better to mount the resistor on the ground
> and run a wire up to the antenna, or mount the resistor at the top of
> the downlead right at the end of the antenna?
Makes no difference at all, unless there could be a standing pool of
water that might cover the resistor.
> crops are harvested I plan to add some additional length to the
> antenna and let it gradually slope to the ground.
Won't do a thing, except get in your way. Ten feet of vertical drop
is ten feet of vertical, whether you slope it for 50 feet or bring it
straight down. Think about the K9AY antenna or Pennant. They act
exactly like two short verticals phased, even though they slope. As a
matter of fact, the Pennant has exactly the same signal pickup on the
pointed end as the perfectly vertical end.
Sloping the wire to reduce vertical sensitivity has to be one of the
biggest
myths ever started. If it worked....the Pennant and K9AY would
immediately stop working. Save the neck of a baby cow, and bring the
wire down vertically.
73, Tom W8JI
W8JI@contesting.com
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