Clay, my Hy-Gain Hy-Tower vertical antenna is mounted with no concrete
and no radials on top of a 36x72 metal barn (NICE COUNTERPOISE). The
base of the antenna is at about 25 ft above grade. At over 75 feet it
is by far the tallest thing around and so is a target for collecting
static electricity.
Neons (depending on which you use) typically ionize and conduct at about
60 volts depending on how bright the ambient light is shining on them.
When they do conduct they make significant RF noise.
I wrapped plenty of small copper wire around a scrap of PVC pipe. One
layer of wire, adjacent windings no spacing and as neat as I could. I
then inserted this RF choke into a larger scrap of PVC and
waterproofed/sealed the ends with GE II silicone caulk (RTV) and then
placed the choke across the ground and antenna feed at the location of
the BALUN feeding the antenna.
I looked up the necessary formulas for the size of the wire, number of
turns/length, and diameter of the form to ensure I had more than enough
X sub L at the low end of 160 meters. so that the RF choke would
basically be seen as an open circuit to the RF on all 8 bands I use it
on but of course be a short (or very low resistance) to static charges.
The DC path to ground via the RF bleeds off static charges without the
RF noise associated with gas discharge tubes such as neons etc.
I have no illusions regarding the survivability of the DIY choke in the
event of a direct hit but so far so good over a year into its life and
it would be simple and cheap to replace it. I do not depend on it to
handle a strike. I have store bought in-line coaxial lightning
suppression devices. Since it drains charges down to the zero volt
level I think it drains static charges that the tall (75 feet above
grade to the top) gathers and reduces the likelihood of a direct
hit.Should the antenna take a hit the choke will be toast and I'm out a
dollar or so to replace it. Meanwhile, it is electrically quieter.
I'm open for suggestions to improve my situation. Although the ham
population in my zip-code has doubled in the last couple years (I took
the other guy to the exam venue so he is a tad new to offer well
seasoned advice) I still have to rely on books and the internet for
getting ideas other than my own.
Patrick NJ5G
On 3/27/2014 10:02 AM, Clay Jackson wrote:
Very interesting discussion! Thought I'd share a little bit about my
shack - we're in Eastern Washington, in the middle of what used to be a 90
acre wheat field. I have a HyGain AV18HT (50' vertical) about 200' from
the house, and then a couple of VHF antennas on 30' masts bracketed to the
side of the house.
When we had the house built, before the foundation was poured, I cadwelded a
#2 copper wire to one of the rebars in the middle of the foundation and left
it out. After the house was completed, I cadwelded that wire to an 8'
copper rod, then ran #2 wire around the 3 corners of the house, with an 8'
rod at each corner, all cadwelded - I also cadwelded that to the house AC
"Safety" ground, which is just another piece of rebar tied to the foundation
that comes up through the garage floor near the electrical panel.
I have a DX Engineering Entry Panel, and my #2 copper wire terminates in
that panel, with the wire clamped to the aluminum plate inside the panel.
All of my antennas except the vertical enter through that panel, through
lightning arrestors bolted to the panel. The VHF antenna masts are mounted
in a pipe sleeve buried at least 4' into the ground, and there's an 8'
ground rod at each mast, cadwelded to the round-the-house ground wire.
The HyGain Antenna is mounted on a 6x6x6 block of concrete - the "legs" were
clamped to the rebar in the concrete, and I left one of the pieces of rebar
above the concrete, to which I clamped the antenna ground and lightning
arrestor at the base. The AV18HT feeds the tower at the base (the legs sit
on insulators); and so I have a box with 8 neon bulbs in it connected
between the tower and ground as a static discharge.
In the shack, I have a 6' strap of 2" wide copper braid, bolted to a 6'
long 2" copper pipe that sit on the back of my operating table. All of my
gear is connected to that pipe with 1/2" or bigger copper braid. The
operating table frame is constructed of 1x1 steel tubing, and that's also
connected to the ground pipe. All of my power comes through a generator
backed set of 3 UPS, 1 1500VA and 2 450VA.
So far, I haven't had any DIRECT strikes; but, last year, we did get a
strike about 100' from the base of the tower that was pretty intense - no
damage to any of the rigs or other devices.
Clay
N7QNM
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Jim
Brown
Sent: Sunday, March 23, 2014 9:37 AM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Back of desk grounding buss
That experience counts for lightning protection of commercial installations
with big budgets, setups that don't change, no local analog audio, and in a
broadcast environment, balanced audio. But that's not most ham stations. We
have limited budgets, we do everything ourselves, we change our setups as we
try new things, buy new gear, have lots of stuff interconnected, like
computers, rigs, amps, audio processors, SO2R boxes, and all of the
interconnections are UNbalanced.
Moreover, if it's FM broadcast, cellular, or VHF/UHF 2-way, most of those
antennas are high in the air and have nulls in the direction of the
equipment, whereas our antennas often produce significant field strength in
our shacks.
Those interconnections, especially analog audio, is one big reason why
chassis-to-chassis bonding is far better than running individual wires to a
common point (or bus bar).
And there is nothing about that chassis-to-chassis bonding that is less good
than individual wires to a common point. Remember that with those wires to a
common point, we still have a loop to create magnetic coupling -- it's
formed by the interconnections between the boxes and those long wires to the
common point.
73, Jim K9YC
On 3/23/2014 8:44 AM, Jim Lux wrote:
Your experience is probably more relevant. Especially with reference to
commercial practice.
My thing is more about the theory behind the recommendations, which is
often buried in the mists of history. Sort of like 468/f
On Mar 23, 2014, at 3:53, n4zkf<towertalk@n4zkf.com> wrote:
I didn't put a rover on mars but I do grounding on cell and
broadcast sites for a living working in telecom. Does that count?
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