Grounding Tower & Shack (Advice Needed)
Private
I am looking for some advice on if the ground system featured below is
sufficent or should be upgraded. It consists of:
- 3 ground rods 10' each around the tower (bonded together)
- 2 ground plates (one outside, one in the shack, also bonded
together)
- lightning arrestors and/or feedthrough adapters
- tower to mast ground
- interior coax switch (not shown)
I provided some pictures below:
http://www.telusplanet.net/~homac/exteriorground01.JPG
http://www.telusplanet.net/~homac/exteriorground02.JPG
http://www.telusplanet.net/~homac/exteriorground02a.JPG
http://www.telusplanet.net/~homac/exteriorground03.JPG
http://www.telusplanet.net/~homac/exteriorground04.JPG
http://www.telusplanet.net/~homac/interiorground01.JPG
http://www.telusplanet.net/~homac/interiorground02.JPG
I am looking for constructive feedback.....
Thank-you....
Lloyd
Jack Painter
> - 3 ground rods 10' each around the tower (bonded together)
> - 2 ground plates (one outside, one in the shack, also bonded
> together)
> - lightning arrestors and/or feedthrough adapters
> - tower to mast ground
> - interior coax switch (not shown)
>
> I provided some pictures below:
>
> I am looking for constructive feedback.....
Hi Lloyd. Certainly an extremely professional appearance to the work. Great
to see such attention to detail as your station provides. Feedback now.....
Is that nice drainage-rock surrounding the tower base only a couple inches
deep? Seems the ground rods lose effectiveness for whatever depth that rock
is. Would have been fine to sink them a full 10' even after digging a 1'
deep trench and covering with topsoil. Besides gaining addtional
effectiveness from the ground, it's the exposure to air that will cause the
most need for future ground system maintenance.
Ground rods around the tower are very close together, is there room to add
additional ground rods from at least two of the legs at a distance of 10-20'
from the tower?
Tower is very close to, but not bonded to the house. Are there metal rain
gutters or metal flashing close by? Bonding to them is indicated, if so.
Is that a picture of coax shield grounding design, using the SS hose clamps?
Stainless steel is a very poor conductor and works when nothing else will -
but a copper or bronze shield-ground would be better. Andrews Wire and I.C.E
both make nice ones.
Interior surge protection for wiring is going to be a serious issue, when a
tower is that close to the structure. EMI from a direct attachment so close
will be a challenge that might indicate 200% sizing of neutral wiring,
double-ended surge protection and some very good bonding. Ground Potential
Rise will start right at your station's single point ground with a tower so
close - therefore perfect bonding including the connection to the AC service
ground is essential. In that respect, those attractive looking insulated
wires bonding the station equipment to the single point ground may be
inadequate. The bonding is the only protection from such close aboard GPR,
and individual heavy, wide copper straps could do a much better job than the
wiring shown.
All in all, I think the only major defect is the lack of additional ground
rods, as when a tower is right next to you, the desired direction for
attachment current is away, away, away. Carry it away with a ground field
that uses very heavy low impedance conductors and at least two more ground
rods. More is better considering where your tower is.
Best regards,
Jack Painter
Virginia Beach VA
**THE-RFI-EMI-GUY**
protector to those conductors passing through the terminal block on the
ground plate.
Make sure everything in your shack is bonded together, including your
computer etc. Add protection to phone lines. etc.
The other poster mentioned more ground rods. That is a good idea,
arrange them to direct the current away from your shack.
Have you bonded this ground system to the rest of the house? If not, do
so by running a conducter to the utility ground rod. Be careful doing so
as there may be a slight potential difference that will go away when
bonded. Also check your water supply. Is it mettalic? Then bond it as well.
Private wrote:
--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"
"Jazz is not dead, It just smells funny" F.Z
K9SQG
before storms arrive is a good idea in any case...
Harry Conover
Hi Lloyd,
Looks like a nice installation, although your grounding rods might be
placed farther apart, or augmented by some heavy gauge radial wires
(depending on your local ground condictivity).
What I did note missing was the mention of 'lightning chokes' wound in
the coax lines decending from the tower. These are basic to lightning
protection for broadcasting towers, but I've rarely seen them
implemented by hams.
The idea of a lightning choke is to add a small amount of inductance
to the coax so that if a direct lighting strike happens, the
instantaneous current flowing though the outer jacked of the coax into
your lightning arresters will at least have some amount of impedance
limiting the current magnitude, thus reducing the probability of
destruction of both the coax and the the arrester itself.
These chokes are more often than not implemented by winding a dozen or
more turns of coax around a form (say a 4" diameter phenolic tube)
prior to the arrester or spark gap.
Harry C.
Jack Painter
"Harry Conover" <hhc...@yahoo.com> wrote
Harry, that winding of coax may be useful as an RF choke, but it is most
certainly not a lightning choke, and will act more like an air-wound
transformer than anything else. Not only is this not specified for any
lightning protection systems, it is specifically warned against in many.
Dr. Daffodil Swain
--
Listen to Alternative News and Conversation You Won't Hear On Commercial
Radio.
Visit http://live365.com/stations/pascoradio
YOU HAVE BEEN WARNED!
First Time Users May Be asked To Do A 1 Time Setup.
"Jack Painter" <223...@cox.net> wrote in message
news:r4_Rc.12079$Yf6.1279@lakeread03...
> Hello All. First let me comment that the lightning mitigation techniques
used are better than many ham installations. That being said, I would
increase the conductor size between the tower legs and the ground rods.
When I saw these, I thought a "fast acting fuse." The amount of current
that the tower can handle cannot be safely terminated to ground with smaller
conductors.
Also, the screw terminals need to be checked periodically because they will
loosen themselve due to "cold flow." Why not repace them with crimp types
and then solder the crimp with a torch as a back up? I am asuming that this
device is covered by something to protect it from rain, etc?
John-WA4JM, Dade City, FL, home to some of the most ferocious lightning
activity in the western hemisphere.
Harry Conover
> > radio-o...@telus.net (Private) wrote in message
> news:<d318809e.04080...@posting.google.com>...
> >
> > What I did note missing was the mention of 'lightning chokes' wound in
> > the coax lines decending from the tower. These are basic to lightning
> > protection for broadcasting towers, but I've rarely seen them
> > implemented by hams.
> >
> > The idea of a lightning choke is to add a small amount of inductance
> > to the coax so that if a direct lighting strike happens, the
> > instantaneous current flowing though the outer jacked of the coax into
> > your lightning arresters will at least have some amount of impedance
> > limiting the current magnitude, thus reducing the probability of
> > destruction of both the coax and the the arrester itself.
> >
> > These chokes are more often than not implemented by winding a dozen or
> > more turns of coax around a form (say a 4" diameter phenolic tube)
> > prior to the arrester or spark gap.
> >
> > Harry C.
>
> Harry, that winding of coax may be useful as an RF choke, but it is most
> certainly not a lightning choke, and will act more like an air-wound
> transformer than anything else. Not only is this not specified for any
> lightning protection systems, it is specifically warned against in many.
> Jack Painter
> Virginia Beach VA
Jack, while I'm sure that you believe this, I really can't guess where
you obtained such IMHO such massive misinformation.
First of all, it is the purpose the the coiled coax to act as an
inductor (r.f. choke) because this is how it resists the very rapid
di/dt common mode characteristic associated with a lightning hit, thus
limiting the peak discharge energy that the following spark-gaps and
lightning suppessors must absorb and reducing the overall peak impulse
power damage potential.
It's basically a brute-force version of the common computer technique
of placing a ferrite torroid around cables to attenuate their common
mode impulse transmission/conduction ability. Realize that with
sufficiently low SWR, currents through both the inner conductor and
outer shield of a coax are equal, summing to zero, hence there is no
net electromagnetic field produced. The same is not true for a common
mode impulse traversing the transmission line. The bottom line is that
only the common mode impulse resulting from a lightning strike will
experience the results of the "choke".
I'm not sure why you would believe that a coil of coax would act like
a 'transformer' of any type, unless the SWR is truly enormous, a
probem in itself. A case in point is that in both proton synchrotrons
(typically operating in a swept frequency range of roughly 3-30 Mhz),
and in large phased array radars (some of which operate in the UHF
range) employ multiple feeder coax transmission lines that are cut the
the same electrical length, with the cable lengths in excess of the
required physical run length being coiled up somewhere in the system.
There is no net significant electrical effect on the cable's
transmission characterists in either case.
Prior to completing my degree work at Drexel, I spent 8-years
installing and maintaining broadcast transmission systems ranging from
5-Kw to 50-Kw. This included 5 years as chief engineer in one station
(WBUD in Trenton, NJ) plus part-time work for WFIL, WCAU, and KYW in
Philly. (Additional work in 4 or 5 smaller stations.)
Quite honestly, I can't remember a single one of these that did not
protect their very costly antenna installations, transmitters, and
on-air reliability without lightning chokes employed in their
transmission lines. Still, these broadcasters use equipment that, in
general, nothing more sophisticated than your average ham station, but
on steroids! True, the average AM broadcasting tower usually exceeds
200-feet, but in an intense lightning storm, a 40-foot ham tower is
fully capable of experiencing the same energy lightning hit!
I purchased my first ham receiver, an SX-71 from a ham named Bob
Rutkowski (sp?) in Trenton, NJ. A day or so before I picked it up from
him he took an evidently direct lightning hit on his 40-some foot
crank up tower holding a 2M beam that was attached to his house. He
had grounded the outer shield of the RG-8U coax at the based of the
tower, but without a lightning choke in the coax, the hit simply
vaporized the majority of his RG-8U, his grounding connection, and
most of the final tank circuit in his rig in the basement! Not a
pretty sight!
Realize that a commercial radio broadcaster has to survive episodes
like this without disruption of their operations. Hams don't. Still
the emulation of the broadcaster's time proven protection techniques
involves only a small additional cost to an otherwise excellent
installation.
For more information, see:
Edmund LaPort, "Radio Antenna Engineering", McGraw-Hill Book Company,
New York. (My issue carries a 1952 copyright, still it's an 'oldie but
a goodie' with many subsequent editions -- and AFAIK is still the
bible of the broadcasting industry.)
IIRC, early editions of the ARRL Handbook also described this
protection technique (likely pre-1970) in the days when most hams
built their own rigs.
Harry C.
p.s., Jack, I'd love to hear a citation where "it is specifically
warned against", and why.
Private
rotator cable ground. Not sure what to do about the lightning choke.
I don't mind replacing the antenna/mast if I receive a direct
lightning hit, I just dont want to turn be fried to a crisp.....
Lloyd
hhc...@yahoo.com (Harry Conover) wrote in message news:<7ce4e226.0408...@posting.google.com>...
Jack Painter
"Harry Conover" <hhc...@yahoo.com> wrote in message
news:7ce4e226.0408...@posting.google.com...
Hi Harry - well, the web is FULL of massive information, and the old trick
of coiling coax for lightning protection is simply not specified any longer.
I will look up the sites which warned against it, citing amplification of
EMI by such a manuever, and get back to you.
>
> First of all, it is the purpose the the coiled coax to act as an
> inductor (r.f. choke) because this is how it resists the very rapid
> di/dt common mode characteristic associated with a lightning hit, thus
> limiting the peak discharge energy that the following spark-gaps and
> lightning suppessors must absorb and reducing the overall peak impulse
> power damage potential.
Arrestors AND shield grounding are specified at the TOP and BOTTOM of the
towers, and AGAIN at the facility entrance. No coils are shown in modern
drawings of lightning protection, and I have and reviewed those of one the
largest communication companies in the US.
Realistically, such a coil never had any chance of slowing down a 8us/20us
or faster attachment of 100,000,000v or even a fraction of that in the
smallest of strikes. Coax can only carry 4,500v before the dialectric breaks
down and then your SWR and balanced currents are no longer part of the
playing field. At about 5,500v the coax can no longer carry the energy by
itself and will arc over to anything nearby. So diverting 99.9% of the
energy via a fast acting suppressor and shield grounding is the only hope
for coax which does in fact take an attachment. Most times the coax does NOT
receive the direct attachment! So after shield grounding and arrestor
connection, the coiling isn't necessary in the first place, would do no
good, and can most certainly act as an air wound transformer to EMI if
"wrapped in a dozen or more turns" as you said. Even one turn. Fortunately,
coax is "resonant" (used only as an example for high-velocity and low
impedance) to a fairly small portion of the DC and AC component of a direct
attachment. Not so to the EMI near field, which any wire regardless of it's
velocity or impedance will be subject to inductive coupling of EMI. The coax
shield will absorb most of that EMI, and unless it exceeds 4500v (very
possible in a 50 percentile strike) will be diverted harmlessly to any
nearby shield ground. 12 turns of the coax shield - you do the math as you
are an electrical engineering expert here - what's the voltage out from
4000v in? Yikes.
You will Harry!
Best regards,
Jack
Jack Painter
(sorry if this posts twice - my ISP has newsgroup problems)
Hi Harry - well, the web is FULL of massive information, and the old trick
of coiling coax for lightning protection is simply not specified any longer.
I will look up the sites which warned against it, citing amplification of
EMI by such a manuever, and get back to you.
>
> First of all, it is the purpose the the coiled coax to act as an
> inductor (r.f. choke) because this is how it resists the very rapid
> di/dt common mode characteristic associated with a lightning hit, thus
> limiting the peak discharge energy that the following spark-gaps and
> lightning suppessors must absorb and reducing the overall peak impulse
> power damage potential.
Arrestors AND shield grounding are specified at the TOP and BOTTOM of the
>
You will Harry!
Best regards,
Jack
Jack Painter
(sorry of this posts twice, ISP has newsgroup problems)
Hi Harry - well, the web is FULL of massive information, and the old trick
of coiling coax for lightning protection is simply not specified any longer.
I will look up the sites which warned against it, citing amplification of
EMI by such a manuever, and get back to you.
>
> First of all, it is the purpose the the coiled coax to act as an
> inductor (r.f. choke) because this is how it resists the very rapid
> di/dt common mode characteristic associated with a lightning hit, thus
> limiting the peak discharge energy that the following spark-gaps and
> lightning suppessors must absorb and reducing the overall peak impulse
> power damage potential.
Arrestors AND shield grounding are specified at the TOP and BOTTOM of the
>
You will Harry!
Best regards,
Jack
Jack Painter
grounds will top it off. Stay tuned for the looping coax fiasco finale....
Jack
"Private" <radio-o...@telus.net> wrote in message
news:d318809e.04081...@posting.google.com...
King Zulu
> Hello,
>
> I am looking for some advice on if the ground system featured below is
> sufficent or should be upgraded. It consists of:
>
> - 3 ground rods 10' each around the tower (bonded together)
Lightning likes to go straight. Try to have at least one ground rod
connected to the tower base at the base; the rod should be directly under
the base or as close to touching the base as possible. A 10' ground rod is
good if in conductive earth. In sandy Florida, where I tood several hits, it
took over a 20' length of ground rod (1/2" steel water pipe) to hit
conductive "hard pan". I just washed it in until it hit some solid clay,
and then washed it into the clay as far as I could.
> - 2 ground plates (one outside, one in the shack, also bonded
> together)
> - lightning arrestors and/or feedthrough adapters
> - tower to mast ground - interior coax switch (not shown)
The coax switch should be a grounding switch. Floating elements on an
antenna could actally attract a lightning hit. Also, for induced hits (not a
direct strike, but with enough voltage to damage equipment due to a nearby
strike), the grounding of the antenna lines gives the charge a nice safe
path to follow. That's better than letting the current find its own path by
arcing somewhere. I like to turn off the AC power to my entire equipment
setup when not in use. So, with the power switch on the transceiver and the
main "shack" ac power switches off, a lightning surge on the power line can
only get me or the equipment when I am actually operating. One last
suggestion: put a big (3 or 4' diameter) vertical loop (preferably near the
ground) in all tower cables going into the house. (Right over your ground
plate might be a good place.) The inductance of the loop, and the fact that
lighting likes to ionize paths in a more or less straight lines, will keep
the main current surge of a direct hit from entering your house and finding
its "home" in your power line or telephone line. I survived operating for
many years in the lightning belt of Florida and have the burn marks on my
mast to prove it. The only known damage in Florida was some induced power
that killed a couple of ICs connected to a printer ribbon cable. That was
just from the current going down the tower on the outside side of the wall.
Lightning protection is still as much art as science, Lloyd - but what you
have done so far should fairly well protect folks in the house. If lightning
is going to hit, just let it find a nice safe home - and try not to be
operating when it does. HI HI
In Florida, a house one block from us burned to the ground when lightning
started a fire in their attic. That couldn't have happened at our house, as
the lighting had a 70' tower to hit first, and a 23' ground rod to give the
current a safe place to go. We were hit - several times. So, look at your
well grounded tower as an asset for true lightning protection - not a
liability.
73
ak
Richard Clark
wrote:
>Thank-you for the advice to this point. I think I will invest in the
>rotator cable ground. Not sure what to do about the lightning choke.
>
>I don't mind replacing the antenna/mast if I receive a direct
>lightning hit, I just dont want to turn be fried to a crisp.....
>
>Lloyd
Hi Lloyd,
Of the advice offered, out of the dozen or so comments, only the
addition of radials and grounding of peripheral equipment made any
sense to your already extensive installation. Adding "more" rods
sounds like hail Mary solutions. I would bet almost every house for
10 miles around you survives quite well with one.
Sure, few if any sport towers, but lightning in the vicinity is not so
choosy as to miss every house, building, or power pole simply because
they are not radio amateurs.
I also note the complete absence of discussion about the Code. All
grounds must be bonded (clamped, not screw attachment nor
solder/brazed) with a continuous wire (no breaks or splices). I also
note some rather bizarre descriptions of how chokes work (and to add
that they are not used by Hams is simply ignorance or the choice to
illustrate with poor examples).
I would suggest you mine the archives of rec.radio.amateur.antenna for
two correspondents: Richard Harrison, KB5WZI for thousands of
commercial and amateur tower installations over a career spanning 50
years (you will discover half to two thirds of suggested
embellishments are immaterial fluff); and Reg Edwards, G4FGQ for the
topic of successful ground rod application (notable in that laying
them horizontal is just as good, if not better).
As to your last comment about getting fried. You should examine that
illusion and recall that it brings voltage to mind, not current.
Voltage comes from two mechanisms common here, impedance and
resistance (the lightning strike is considered to be from a constant
current generator willing to present any potential necessary to
preserve flow). A sharp bend in a conductor is one source of
impedance change for the bad - so graceful sweeps are preferred where
you want to change direction. I note the irony of discussion where
chokes are used to build voltage (power being equal to I·E and current
being constant guarantees a build up of power beyond what would have
been suffered) to guarantee spark discharge elements firing (I suppose
so, but this sounds like Advertising Copy to sell spark discharge
elements). Most successful solutions offered here for years and years
all have the common goal of burying the lightning stroke's current
into the soil as soon as possible without any impedance to its path.
If you research the archives for low resistance paths of lightning,
you will find out how little total power is suffered in a strike
(don't fall for the monster under the bed stories of a gazillion volts
at a bajillion amps).
73's
Richard Clark, KB7QHC
Red Noise
http://www.polyphaser.com/
Engineering notes at URL:
http://www.polyphaser.com/ppc_pen_home.asp
--
Red Noise
Michael Waldrop
I recall a technical article from "PolyPhaser.com", the lightning product
company. Below is an exerpt from the technical document covering Amateur
Radio lightning protection and coiling of coax cable to form a choke.
Quote:
(from www.polyphaser.com website)
Document Number PEN1016: An overview of Lightning Protection for Ham
Radio Stations
Even though the inductive properties of the coax cable appear to be
beneficial, and extra inductance can be created by adding a few turns to the
coax; don't do it. The added turns can also act like an air wound
transformer coupling more energy into the line. Make sure coax lines leaving
the tower remain at right angles to the magnetic field surrounding the
tower.
Unquote
It is my belief, based on coils and induced energy into the coil, that
coiling of the coax will induce an EMF field that can be picked up by the
coax, or other cabling, allowing it to enter into the house/shack or, more
simplified, follow a path that is not desired, i.e. the coax or rotor cable
run to the shack. Grounding of the coax at the top and bottom of the tower,
attaching coax lightning protecting products at the base of the tower and
running the remaining coax to the shack through buried metal conduit,
greatly reduces the chances of lightning strike energy from entering into
the cable(s) leading from the tower. Additionally, each leg of the tower,
not just one leg, should be grounded through it's own seperate ground rod
and each leg ground should be connected to a circular grounding system,
around the tower. The tower grounding system should be further connected to
a house grounding system surrounding the house with 8 foot grounding rods
driven into the ground and connected to the house grounding system (central
point grounding). The tower grounding system along with the house grounding
system should be connected together. The distance between the tower and the
house/shack can be lengthy. Connect the 2 systems together and add
additional 8 foot grounding rods every 16 feet along it's path.
Using buired conduit for coax and rotor cable, for example, greatly reduces
the chance of EMF fields from flowing along the coax and into the shack. A
direct lightning strike to the tower will generate an EMF magnetic field
that can be picked up by coax, rotor and coax switch cables then flow into
the house and through the equipment and/or wiring. The tower, during a
direct strike, radiate a large EMF magnetic field that can be picked up by
anything within it's path. The strength of the field reduces by a factor of
1, outlined in the Polyphaser.com technical document.
Just some technical information I've found from lightning protection
companies during my search for documentation on tower, antenna, coax and
rotor cable installation.
73's,
Mike
WB8TNJ
"Harry Conover" <hhc...@yahoo.com> wrote in message
news:7ce4e226.0408...@posting.google.com...
> "Jack Painter" <223...@cox.net> wrote in message
Jack Painter
http://www.comm-omni.com/polyweb/hamradio5.htm
Even though inductive properties of the coax cable appear to be
beneficial, and some extra inductance can be created by adding
a few turns to the coax; don' t do it. The added turns can also
act like an air wound transformer that can couple more energy
into the line. This is just the opposite of the desired effect.
Instead, make sure that coax lines leaving the tower remain at
right angles to the magnetic field surrounding the tower.
http://www.wrblock.com/Papers/Amatuer_Radio/APARS_P09.htm
Neatness counts - cables (transmission lines, power (ac and dc),
speaker, microphone, computer, control) should be cut to length
and routed neatly and cleanly between boxes using the most direct
practical route. The coiling of excess cable length on the
protected side should be avoided since it could act as an air-wound
transformer coupling magnetic energy from a nearby lightning strike
back into the protected equipment.
http://www.marcspages.co.uk/tech/2100.htm
Some in the RF industry would have seen coils used as static drains.
The theory is the coil is high impedance at RF and so looks open
circuit, whilst still presenting a short to the DC and draining it
to deck. The problem with them is they too can start reacting
('scuse the pun!) with the capacitance present on the system,
especially at the lower ends of the band.
24hr ops FULL COVERAGE PROTECTION (no "chokes")
http://users.erols.com/n3rr/lightningprotection/
http://www.alvarion.com/RunTime/Materials/PDFFiles/Lightning_Protection_White_Paper_March31_R41.pdf
ALVIRON SUBSCRIBER SYSTEMS TOWER LIGHTNING PROTECTION
(no "chokes")
And one major US communications company which drawings and specs
are confidential and proprietary information - but they do NOT use
any kind of coiled-coax and prohibit same from all systems.
Here's one exception - from an Amplifier and relay company - they
are NOT in the lightning protecton business and this is very
outdated advice, but shown anyway becasue we're honest!
http://www.ameritron.com/ameritron/man/pdf/RCS-4.pdf
We strongly recommend the use of lightning retarding loops
in the coaxial cables near the relay box (see illustration).
Remember that lightning travels through the path of least
resistance. Station ground leads should be solid, large surface
area conductors. Do not use braided or stranded wire for the
ground leads. Avoid sharp bends in the ground leads. Use
multiple ground rods and/or radials to provide the earth
termination.
---
Recommend you ignore this and maintain direct paths - JP
Finally, Richard Clark's mention of "code" is pretty important. Reference
the NEC-70 and NFPA-780 for US installations.
Jack Painter
Virginia Beach VA
http://members.cox.net/pc-usa/station/grounding.htm
Private
Although I really appreciated the information, I do not want to get
too hung up on the coiling of the coax. This weekend I plan to
upgrade the gauge of the wire from #8 to #3. Also I have now bonded
the cold water pipe entering in the basement floor to the exterior
ground plate.
Any other feedback on the pictures below are appreciated......
Lloyd
- 3 ground rods 10' each around the tower (bonded together)
- 2 ground plates (one outside, one in the shack, also bonded
together)
- lightning arrestors and/or feedthrough adapters
- tower to mast ground
- interior coax switch (not shown)
I provided some pictures below:
http://www.telusplanet.net/~homac/exteriorground01.JPG
http://www.telusplanet.net/~homac/exteriorground02.JPG
http://www.telusplanet.net/~homac/exteriorground02a.JPG
http://www.telusplanet.net/~homac/exteriorground03.JPG
http://www.telusplanet.net/~homac/exteriorground04.JPG
http://www.telusplanet.net/~homac/interiorground01.JPG
http://www.telusplanet.net/~homac/interiorground02.JPG
"Jack Painter" <223...@cox.net> wrote in message news:<9WQSc.16277$Yf6.6584@lakeread03>...
Richard Harrison
"(don`t fall for the monster under the bed stories of gazillion volts at
a bajillion amps)."
Good point! It`s akin to: "You can`t protect against a direct hit!"
Oh yeah? How about 10,000 medium-wave broadcast stations struck by
nearly every charged cloud passing overhead? Sometimes several times a
minute for a long time period. The listener is often unaware of the
instantaneous carrier drops to extinguish the arcs initiated by the
lightning strikes. And, one of the most important lightning opponents is
a large coil of large wire in each tower lighting wire at the base of
the tower. It keeps lightning as well as R-F out of the electrical
service to the station.
If tower lighting chokes stepped up the lightning, they would all be
replaced with Austin transformers or some other technique such as shunt
feed of the radio towers to eliminate the base insulator. Truth is,
lighting chokes are very effective at keeping lightning out of the power
supply.
Best regards, Richard Harrison, KB5WZI
Dave Shrader
> Richard Clark, KB7QHC wrote:
> "(don`t fall for the monster under the bed stories of gazillion volts at
> a bajillion amps)."
It's not a monster under the bed. But it is a heaven of a blast!
The actual USAF specification for lightning strikes is based on a
probability model.
It's been 20 years since I read the actual wording, but the values are;
90% of all lightning strikes in the USA are described as falling within
the spectrum defined by a strike with the following characteristics:
1) Double strike. First peak 100,000 amperes with a second strike of
50,000 amperes. Full Width Half Maximum [approximately 50% pulsewidth]
of 100 useconds for each peak.
2) Rise time from 0 to peak is 1 usecond on both strikes.
3) Fall time is a decaying exponential from peak to approximately 500
amperes sustaining current in the lightning channel for 300 milliseconds.
4) Electric field intensity prior to prestrike is greater than 10,000
volts per meter.
Conclusion: Lightning has lots of energy. Systems have been designed to
not only survive a direct strike but to operate through the direct
strike. All it takes is $$$$$$.
Note: 50% of all strikes use the same pulse width model but with a
reduced amplitude of 20,000 and 10,000 amperes for the peak values.
W1MCE
Program Chief Engineer, retired
USAF MX MIssile RS/RV, WS-118
Jack Painter
"Richard Harrison" <richard...@webtv.net> wrote in message
news:19863-41...@storefull-3255.bay.webtv.net...
Hi Richard, really glad to see you chime in. Even ignoring the few examples
I found that argue against the choke concept, what was more relevant to me
was that in poring over hundreds of documents lately, I can find no modern
specification for coiling the coax at any point, high or low. Not in the NEC
or NFPA, not in the descriptions and specs to nationwide antenna tower
systems, and not in National Lightning Safety Institute, University of
Florida or other acedemia writings of such protection systems. So what seems
to remain, is its record of use, perhaps prominently at one time, without
evidence that the design was ever effective. Remember that for 230 years
science seemed to support the pointed lightning rod without really testing
it against other attachment points. Now it is fairly well agreed that
blunt-tip rods were sceintifically tested to do a much better job of
attracting the leader that was headed for a given area anyway. Perhaps the
colied coax chokes are just fading away due to no real evidence that they
work, and some theory and maybe even feeble arguments that they could do
harm. From an EMI standpoint, it's hard to argue the concerns. And from
direct attachment, only a massive winding of very heavy conductor could slow
down lightning (providing there was an arc-gap for it to take as an
alternate to that slowdown). Might be why the modern lighter cabling of
todays proliferant towers find little usefulness for the concept - just as a
possibility.
Best regards,
K9SQG
v CMOS circuitry...
Richard Clark
<david....@comcast.net> wrote:
>Richard Harrison wrote:
>> Richard Clark, KB7QHC wrote:
>> "(don`t fall for the monster under the bed stories of gazillion volts at
>> a bajillion amps)."
>
>It's not a monster under the bed. But it is a heaven of a blast!
Hi Dave,
The point of the monster is that it is NOT under the bed, but in the
heavens. Let's look at the numbers you provide:
>First peak 100,000 amperes with a second strike of
>50,000 amperes. Full Width Half Maximum [approximately 50% pulsewidth]
>of 100 useconds for each peak.
Expressed as power into a section of tower where the cumulative
resistance is 1 mOhm (not unreasonable) and giving the stroke a full
second sustained current flow (I've never seen such a long one) so we
can round the numbers into watt-seconds (never mind KWH); and figuring
a duty cycle of 0.01% based on your pulse width, but let's get
extravagant and say 0.1%; then both strikes express all of 150
milli-watt-seconds of power.
>
>500 amperes sustaining current in the lightning channel for 300 milliseconds.
Again, expressed in watt-seconds (sneering KWH) this probably doubles
the power burden another 150 milli-watt-seconds. Total power: less
than half a watt-second or as much heat as 1/10th of a Christmas tree
bulb held for the same time as the strike. For those who remember
NE-2 bulbs in their radio's front end, these are rated at 1/4 Watt.
The paranoid may wish to parallel several, but such devices exhibit
what is called current hogging - one will fire to destruction before
the others light up.
To demonstrate the catastrophe that is so often associated with a
strike, divert the same strokes to a nearby tree that shows all of 10
Ohms resistance in its sap: 3 KW-Seconds. Try holding three clothes
irons for 1 second. :-)
Even this is barely remarkable given the heat is spread over a
considerable bulk. What makes the difference so destructive? That
same time element. The heat does not have the leisure of dissipation
in 100猶 and concentrates. This accounts for the scoring of a strike
on metal, or the steam explosion in a tree trunk.
>4) Electric field intensity prior to prestrike is greater than 10,000
>volts per meter.
>
>Conclusion: Lightning has lots of energy.
Energy is a strange thing, sunlight has vastly more energy than radio
waves at HF (or VHF or UHF or SHF or....) No one worries about their
radio at the beach, but they put sun screen on their skin. Walking
across a wool carpet generates far more energy than a pre strike, but
hardly enough power for a pinwheel. Separating two sheets of typing
paper is about the same risk.
This does not diminish the liability to sensitive components. The
electric fields created by the casual separation of paper can destroy
a transistor IFF it is not in a circuit. The power absorbed by
common, resistive components in relation to that same transistor
protect it simply. There are some circuit designs that seek a high
input resistance that easily fail to this assault. I should note that
in this day and age of surface mount that there are also resistors
that can be destroyed by these casually generated potentials.
>Systems have been designed to
>not only survive a direct strike but to operate through the direct
>strike. All it takes is $$$$$$.
Well, for the amateur (not working through a strike) perhaps $$.
The risk is: "Do you maintain 0.001 Ohm or better strike paths?"
Jack Painter
"Richard Clark" <kb7...@comcast.net> wrote
Hi Richard - can you please explain this "duty cycle of 0.1%" ? I thought
it was expressed as a 10% duty cycle - but then a 50kva strike would be
expressed as 5kva sustaining current in the lightning channel, not 500
amperes. Dave - was that 500 amperes a typo or the figure used by the USAF
for protection design? My internal surge protection is designed for 10kva
max, and the rooftop downconductors would certainly be expected to carry at
least 5x that much for a short time from a direct attachment. Even internal
AC wiring is designed to carry 6kv/1kva before dialectric breakdown. Which
does incidentally happen from those 100kva strikes. It just happened less
than half a mile up the beach from me last month.
Thanks,
Richard Clark
wrote:
>Hi Richard - can you please explain this "duty cycle of 0.1%" ?
Hi Jack,
Duty cycle is a simple ratio of on time to off time. It would be
presumptuous to offer that the strike off time for any particular spot
on earth is hundreds of years, so the choice of one second is suitably
long enough given strike components have long since faded, but are
easily recent both.
The shape of the pulse complicates the estimate because Duty Cycle is
often expressed in the expectation of a square wave. What is the on
time? When you get into pulse work, most in the field arbitrarily
assign the width of the half-power, or half-voltage points. For
Dave's numbers, this would be some 100µS which, when compared to 1
second is actually 0.01%. Being generous, and given the shape of the
decay I simply threw in a 10X fudge factor.
> I thought it was expressed as a 10% duty cycle
10% of what? Lightning current flows for 100µS and is off for 1mS?
Dave clearly expresses lingering current flow out to 300mS so that is
clearly wrong.
> - but then a 50kva strike would be
>expressed as 5kva sustaining current in the lightning channel, not 500
>amperes.
Where did the volts come from? If the pre strike fields are running
10KV then your strike has only 5A in it. This is the pencil whipping
that comes with lightning: the voltage description. ALL of that
voltage is dropped across 10000 feet of discharge length, not in the
last 3 inches from the tip of the bolt to ground.
In normal, settled air, in the most benign weather without any
disturbance, the potential gradient from earth to sky is 180V/M. That
is to say, your head is at an elevated potential of 300V with respect
to your feet. At an altitude of 10000 feet the potential is
1,800,000V without any inducement to discharge.
>Dave - was that 500 amperes a typo or the figure used by the USAF
>for protection design? My internal surge protection is designed for 10kva
>max, and the rooftop downconductors would certainly be expected to carry at
>least 5x that much for a short time from a direct attachment. Even internal
>AC wiring is designed to carry 6kv/1kva before dialectric breakdown. Which
>does incidentally happen from those 100kva strikes. It just happened less
>than half a mile up the beach from me last month.
You need to look at those surge protection ratings again. My
experience is that they are rated in Joules capacity which is NOT the
same thing as v-amperes. The two may be equivalent, but your
reference for volts is missing altogether. As I offered in other
postings: where did the voltage come from? If your tower is of the
standard design, you are not going to develop any appreciable voltage
unless you introduce resistance or impedance to develop it from the
current flow. 100,000A through 0.001 Ohms may give you 100V at best,
and only if you can reach the top of tower where the strike hits.
For those who want to multiply this voltage with Z, calculate the
impedance of a 12" diameter wire 50' tall at a frequency of 1MHz.
Perhaps this will make an NE-2 glow, if its leads are long enough.
> It just happened less
>than half a mile up the beach from me last month.
No doubt, but what exactly was "It" that happened? Stick 50 feet of
tower up into the air, and interrupt it with insulation and YES! arcs
will spark. No one needs an insulated $$$$$$ tower - thousands of
commercial installations typically discard that feature in favor of
simple $$ lightning protection.
Roy Lewallen
> . . .
> You need to look at those surge protection ratings again. My
> experience is that they are rated in Joules capacity which is NOT the
> same thing as v-amperes. The two may be equivalent, but your
A joule is a watt-second.
Roy Lewallen, W7EL
Richard Clark
wrote:
Hi Roy,
Quite so. Still missing the volt reference (and no mention of Ohms).
Jack Painter
> On Sat, 14 Aug 2004 16:11:30 -0400, "Jack Painter" <223...@cox.net>
> wrote:
> The shape of the pulse complicates the estimate because Duty Cycle is
> often expressed in the expectation of a square wave. What is the on
> time? When you get into pulse work, most in the field arbitrarily
> assign the width of the half-power, or half-voltage points. For
> Dave's numbers, this would be some 100µS which, when compared to 1
> second is actually 0.01%. Being generous, and given the shape of the
> decay I simply threw in a 10X fudge factor.
Thanks Richard.
> > - but then a 50kva strike would be
Meant to say "ka" sorry.
> >Dave - was that 500 amperes a typo or the figure used by the USAF
> >for protection design? My internal surge protection is designed for
10kva
> >max, and the rooftop downconductors would certainly be expected to carry
at
> >least 5x that much for a short time from a direct attachment. Even
internal
> >AC wiring is designed to carry 6kv/1kva before dialectric breakdown.
Which
> >does incidentally happen from those 100kva strikes. It just happened less
> >than half a mile up the beach from me last month.
>
> You need to look at those surge protection ratings again. My
> experience is that they are rated in Joules capacity which is NOT the
> same thing as v-amperes. The two may be equivalent, but your
> reference for volts is missing altogether.
Only the those destructive MOV power strips get rated in joules ;-)
My normal-mode silicon diode surge suppression is rated in KA (not kva,
sorry again).
http://www.transtector.com/documents/salessheets/1451-001.pdf
the 10ka model has a 12,000 amp surge rating. I located one at the main AC
entrance panel (load side) and one on the station's 240v branch panel.
Transtector also produces "power strip" surge protection that is all silicon
with NO MOV's and NO L-G references. My station has no AC surge protection
references to ground, and all equipment is connected to L-N surge protection
power strips. Except the computer which runs through an Amer.Pwr.Con. UPS -
which although it has an unavoidable L-G MOV, it is first protected by the
two Transtector Fortresses.
> > It just happened less
> >than half a mile up the beach from me last month.
>
> No doubt, but what exactly was "It" that happened? Stick 50 feet of
> tower up into the air, and interrupt it with insulation and YES! arcs
> will spark. No one needs an insulated $$$$$$ tower - thousands of
> commercial installations typically discard that feature in favor of
> simple $$ lightning protection.
>
> 73's
> Richard Clark, KB7QHC
A strike on a home and/or power lines in which the surge was so powerful
that it blew the electric meter clean off the wall of the home (burning the
powerline and the service panel inside the home). I visited when it was
still smoking but they discouraged my camera. I did get a good picture of my
neighbor's pine tree striped from 75' in the air to 6' above the ground,
where it jumped to and split a wood fence. That was about 50' from the end
of my 60 meter dipole which was operating at the time. I'm thinking the
surge protection is working as advertised this summer. At this rate I'll
soon have more examples that just nearby strikes......but hopefully not.
73,
Reg Edwards
"Roy Lewallen" wrote -
> A joule is a watt-second.
==========================
The only trouble with Richard (Clark) is his abuse of the English language.
;o) ;o) ;o)
Punchinello, G4FGQ
Richard Clark
<g4fgq...@ZZZbtinternet.com> wrote:
>The only trouble with Richard (Clark) is his abuse of the English language.
Glad to observe you don't challenge my technical language.
Figured out mud yet? :-P
Dave Shrader
Richard Clark wrote:
> On Sat, 14 Aug 2004 01:08:12 GMT, Dave Shrader
SNIP
h, but let's get
> extravagant and say 0.1%; then both strikes express all of 150
> milli-watt-seconds of power.
Richard, I'm not going to try to out calculate you.
But, please tell the group what the junction temperature of any
semiconductor device is at transient thermal failure at 0.1 and 1.0
useconds.
Twenty years ago the USAF test data indicated that failure occurred at
0.5 microjoules!!! That's 300,000 times more sensitive than your numbers.
Note, it is extremely difficult to really achieve a 0.001 ohm mechanical
interconnect.
Secondly, the major electronic failure mode is from the coupling of the
magnetic field. A di/dt of 10^5/[1E-6] yields a value of 10^11
amperes/second. A one foot length of wire has a self inductance of
approximately one nanohenry [1*10^[-9]] and the di/dt impact is ... 100
volts peak from one end of the wire to the next.
Back in the olden days, twenty years ago, the action integral, that you
calculated was sufficient to burn a 0.5 inch diameter hole right through
titanium that was 0.1 inch thick. Note: the titanium alloy we used
melts at slightly below 2000 degree F.
The design issue is TRANSIENT THERMAL EFFECTS not average heating. At 1
microsecond the heat flow from the stressed area has not started. The
USAF required adiabatic heating as the peak temperature for the starting
condition for the transient thermal analysis. Restated, all the energy
is converted to instantaneous heat and then the thermal stress analysis
would be performed under that constraint.
Conclusion, lightning is a highly stressful environment.
Richard Clark
<david....@comcast.net> wrote:
>Richard, I'm not going to try to out calculate you.
>
>But, please tell the group what the junction temperature of any
>semiconductor device is at transient thermal failure at 0.1 and 1.0
>useconds.
That was covered in another posting.
>Twenty years ago the USAF test data indicated that failure occurred at
>0.5 microjoules!!! That's 300,000 times more sensitive than your numbers.
Current USAF lore holds, rightly, that it is the power supply that
fulfills the failure, junction penetration energy is insufficient to
accomplish this. Turn off the equipment, disconnect leads and NOTHING
HAPPENS! Same pulse = no damage. Damage is not found in the
miniscule power it is found in poor practices.
Shielding is rather simple to accomplish, and taking care of front
door and back door paths is not Rocket Surgery. It takes very little
imagination to withstand these pulses; unfortunately it takes even
less imagination to succumb. The stories of 1 idiot's plight make the
news, not the 1 million survivors' success.
>Note, it is extremely difficult to really achieve a 0.001 ohm mechanical
>interconnect.
For you perhaps, and certainly others who experience lightning's
catastrophic failure, but 1mOhm is no big deal - measuring it is
however. It is simple to enumerate poor examples, but that does not
pass as careful accomplishment being impossible or unlikely.
>Secondly, the major electronic failure mode is from the coupling of the
>magnetic field. A di/dt of 10^5/[1E-6] yields a value of 10^11
>amperes/second. A one foot length of wire has a self inductance of
>approximately one nanohenry [1*10^[-9]] and the di/dt impact is ... 100
>volts peak from one end of the wire to the next.
You are pencil whipping yourself, Dave. You are off by at least 1
order of magnitude in inductance.
As current USAF lore to this matter reveals (and it is nigh on to 25
years stale), huge pulse coupled currents at low frequencies do a
piss-poor job plain and simple.
Saying coupling and making it happen are two different things (per
current USAF lore) and trying to fit 1MHz into a 1 foot wire is loath
to considerably less potential. This is called overplaying your hand,
a direct strike is enough to argue.
>Back in the olden days, twenty years ago, the action integral, that you
>calculated was sufficient to burn a 0.5 inch diameter hole right through
>titanium that was 0.1 inch thick. Note: the titanium alloy we used
>melts at slightly below 2000 degree F.
I've already commented to this specifically.
>The design issue is TRANSIENT THERMAL EFFECTS not average heating. At 1
>microsecond the heat flow from the stressed area has not started.
I've already commented to this specifically.
> The
>USAF required adiabatic heating as the peak temperature for the starting
>condition for the transient thermal analysis. Restated, all the energy
>is converted to instantaneous heat and then the thermal stress analysis
>would be performed under that constraint.
>
>Conclusion, lightning is a highly stressful environment.
Stress also encompasses primitive fear and probably far more so than
the actuality of failure. This is called the probability of big
numbers. In a nation of 280 Million, any individual's once in a
million experience like lightning striking them or near them happens
280 times a year (5 times a week or more) - it misses the other
279,999,720 times tho'. Thus such hair raising stories inordinately
color the topic and are suitable for selling insurance and amulets.
Hence the advertising and $$$$$$ suggested retail cost for "peace of
mind." At that price, if only 0.01% of those 279,999,720 pushed their
credit cards across the counter, that makes for a very profitable
living second only to ENRON.
Moral: "Don't use insulated towers."
Risk: "How well can you reduce R?"
Micro MegaWatt
http://www.polyphaser.com/ppc_pen_home.asp
--
One Watt
To steal ideas from one person is plagiarism;
to steal from many is research.
-- Comedian Steven Wright
"Private" <radio-o...@telus.net> wrote in message
news:d318809e.04080...@posting.google.com...
> Hello,
>
> I am looking for some advice on if the ground system featured below is
> sufficent or should be upgraded. It consists of:
>
> - 3 ground rods 10' each around the tower (bonded together)
> - 2 ground plates (one outside, one in the shack, also bonded
> together)
> - lightning arrestors and/or feedthrough adapters
> - tower to mast ground
> - interior coax switch (not shown)
>
> I provided some pictures below:
>
> http://www.telusplanet.net/~homac/exteriorground01.JPG
>
> http://www.telusplanet.net/~homac/exteriorground02.JPG
>
> http://www.telusplanet.net/~homac/exteriorground02a.JPG
>
> http://www.telusplanet.net/~homac/exteriorground03.JPG
>
> http://www.telusplanet.net/~homac/exteriorground04.JPG
>
> http://www.telusplanet.net/~homac/interiorground01.JPG
>
> http://www.telusplanet.net/~homac/interiorground02.JPG
>
> I am looking for constructive feedback.....
>
> Thank-you....
>
> Lloyd