From:
Fred Hopengarten K1VR 781/259-0088
Six Willarch Road
Lincoln, MA 01773-5105
permanent e-mail address: fhopengarten@mba1972.hbs.edu
Summary on THHN Wire for Antennas [LONG]
March 27, 1998: I am republishing the following summary,
with additions, for those who missed it the first time.
Special thanks to W9CF, of Arizona State University, for
providing the very last post received (received after the
original posting of a summary), with lab results.
Fred Hopengarten K1VR
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From: John Kaufmann <kaufmann@ll.mit.edu>
Subject: Weekend post mortem
Fred,
I would suggest you do post an inquiry to the appropriate
reflector(s) regarding the worthiness of THHN.
Considerations include: electrical properties (velocity
factor, high voltage RF breakdown characteristics of
insulation) and mechanical properties (stretch, breakage,
etc.).
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At 10:18 AM 9/9/97 EDT, K1VR wrote:
W1FV and I are working on a gain array for 160 using sloping
wires. The time has come to select the wire. For cost and
ease of use, I am thinking about using #12 THHN stranded.
This is a readily available (any Home Depot or Home
Quarters) wire which is covered with a jacket which is
oil and abrasion resistant. The biggest problem, I suspect,
is that in an antenna application it will stretch.
John (W1FV) wants to know:
* Electrical properties (velocity factor, high voltage
RF breakdown characteristics of insulation), and
* Mechanical properties (stretch, breakage, etc.).
Anybody have this information for #12 THHN stranded? Is
there a wires web page?
Will publish results. -- Fred K1VR
9/22/97: #12 copper stranded THHN black is 7 cents/foot or
$24.50 for a 500' roll at Home Depot, Waltham, MA.
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From: Brian Beezley <k6sti@n2.net>
Fred, I can't help with the technical details you seek but I
can provide some anecdotal information for the solid-
conductor #14 THHN I got at Home Depot. The wire works fine
as a 40m inverted V. One end happened to rub against a tree
branch and the 600-volt 60 Hz insulation was not effective
in preventing arcing at 500 watts output (the insulation
carbonized and burned through but the copper remained
intact).
One thing that's attractive about the wire is that it's
available in green (a dull, sea green sort of color) or
light blue. These two colors greatly reduce wire visibility
aloft.
Brian Beezley, K6STI k6sti@n2.net
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From: Pete Soper <psoper@encore.com>
I had an 80m dipole up that was made out of #14 THHN.
At various times it was under significant tension. I never
noticed a shift in its resonant point.
I made a 20m lazy-H out of #10 THHN. I think I could
have folded over the Oak trees it was strung between and
there would have still been zero stretch.
This said, THHN is obviously made out of soft drawn
copper and so with enough tension there will be stretching.
The other positive and negative of THHN is the nylon
over PVC insulation. This lowers the velocity factor and
introduces a fudge factor of a few percent into your
designs. I've found this to be a major source of grief for
complex antennas designed with modelers because the modelers
can't account with the VF. It would seem to be a simple
thing, just knock X% off the lengths, but the reality is
vexing. On the positive side the insulation can provide some
benefits. Being able to have current maximums in contact
with trees can be handy (wouldn't expect the insulation to
handle voltage maximum points though). The antenna might be
quieter too I guess.
Pete KS4XG
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From: bschwerdlin@hlb.com (Bob Schwerdlin)
I have used #14 & #12 wire in the past, only to have the
wires break after about 1 or 2 years. The antennas were 2
band "fan" dipoles for 40 & 80M. Most of the
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time it was one
of the 80M legs that broke. It usually happened in the late
spring, after the cruddy Chicago WX and very windy spring
time.
Well, I went to #10 THHN a few years ago and haven't had any
problems since. I do notice that my resonant frequency did
go down a little bit, only I can't be sure of how much.
... Bob, WG9L, V31RC, FP/WB9VLV
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From: aa8u@modempool.com (Bruce Lallathin)
I've used this stuff for years with good success. My five
element delta loop array for 80M is made of #14. Be aware
that some automotive type wire that has an oil resistant pvc
covering may actually have a thin plastic outer layer which
will age when exposed to uv radiation over time and will
flake off. It seems to allow moisture to seep between the
layers too which might cause resonant freq to go down a bit.
My 80M 4-sq is also made of the same wire and it works very
well. This March a major ice storm tore up most of the
antenna farm here. The loops and the 4-sq were damaged by
ice breaking the nylon ropes that held the elements. Jeff,
N8CC did some experimentation with various wire types and
found the pvc covered wire was approx 2-3% shorter than bare
copper of similar gauge. I think I got that right. I suggest
you e-mail him for the info <n8cc@AOL.COM>. My experience
on the low bands tells me that all the cut and try to get
the resonance points due to the proximity of the ground far
outweighs any minor velocity factor in the wire due to
insulation type. -- Bruce
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From: Kevin Drost <kevindrost@prodigy.net>
Yes, THHN stretches. Also, THHN is plastic PVC covered by
clear plastic. The plastic insulation doesn't stand up well
to sunlight. The clear plastic coating cracks and falls off
after two or three years. Otherwise, the wire is fairly
rugged. THHN is used extensively in machine tool industrial
wiring, and construction wiring inside conduit. I think you
could probably get a better price in 1000' rolls from a
electrical supply house or wire wholesaler - there are a
couple BIG ones in Boston. (Celtic Wire & Cable?)
(Northern Wire?) THHN is verrrrrry common, theres lotsa
stock, and the price is low. But it does stretch, and the
insulation falls off. At least that is my experience at
K8LX
.... I would think copperweld is more durable and possibly
cheaper? 'cuz its mixed with iron and not solid copper, like
THHN.
Kevin, WA8ZDT
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From: "Robert Shapiro" <nd3a@worldnet.att.net>
I tried doing a Yahoo search and found a few companies that
offered THHN wire along with some specs, but in my limited
search, none of the specs you desire. Southwire seems to be
the most prominent company. Maybe if you contact them
directly, they may be able to assist you.
73, Rob
Rob Shapiro - ND3A, nd3a@worldnet.att.net
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From: "Robert L. Carroll" <rlc@idt.net>
I don't know the characteristics of this wire other than I
have to cut it a lot shorter than copperweld. I have been
using it successfully, however. Any info you pick up
appreciated.
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From: David Robbins <k1ttt@berkshire.net>
on thhn, i don't think it is uv resistant. i put some up to
run 12v car fog lights for night tower work and it has been
shedding part of its insulation recently. for antenna
elements here i am using 10ga solid pvc insulated
copperweld, this was recommended by k2tr. it is heavy, its
hard to work with, but you won't break it and the insulation
is meant for long term outdoor use (the stuff is actually
rural telephone wire).
David Robbins K1TTT (ex KY1H)
k1ttt@berkshire.net or robbins@berkshire.net
http://www.berkshire.net/~robbins/k1ttt.html
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From: Randy Thompson <k5zd@ultranet.com>
I use #12 THHN for all my wire antennas. The stuff is
great! It is coated, so seems to last longer and stay in
bette
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r shape than just copper wire. It is flexible and easy
to work with. Seems to handle loads and the wind movement
very well (although it will break at the points where there
is lots of flexing under load). I can't say that stretch
has been any problem at all.
Velocity factor? This is wire -- you cut to length and then
trim! ..... Randy, K5ZD
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From: "Scott Lehman N9AG" <scottal@erinet.com>
> * Stretch
Yep, it'll stretch. THHN has a hybrid insulation,
designed to give high dielectric withstand with a thin wall.
In most cases it can be replaced with general MTW wire which
has just a thicker PVC insulation. The overcoat is Nylon,
which does nasty things when it gets wet. Once nylon is
wet, it stays wet. It doesn't affect its 60 Hz properties
too much, but it isn't pretty at RF (mostly at VHF and
above).
> * Electrical properties
> * Mechanical properties
Most THHN and MTW are rated to 600 VAC. The conductor
is copper, laid 6 around 1 stranding in the smaller sizes of
interest. The tensile strength is basically that of the
dead soft annealed copper. I'd never use it as a dipole or
anything that has to support any weight.
I have used it for Inverted Vees and we're using MTW as
an Inverted-L on 160M at N8NR's place. It is supported by a
rope at the 90' high point and has about 30 feet horizontal.
It's been up since January and its resonance has moved from
1825 to 1780 KHz, hi. My guess of velocity of propagation
for either type is 60-65%.
The NEC (National Electric Code) has a lot of specs on
this type of wire, conductor size, stranding, insulation
thickness, etc. Don't have a copy at home, but I can get
more info if you need it. Scott N9AG/J68AS
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From: "Rick Andren" <n9thc@FoxValley.net>
As an employee of Underwriters Laboratories Inc. our
requirements for dielectric breakdown are the working
voltage times two, pluse 1000. This being the case, we test
THHN wire for (600v*2)+1000=2200 volts at 60 Hz. As you
increase the frequency, the dielectric will have a tendency
to breakdown at a lower voltage, and at RF, I think the
insulation is just about transparent.
I have pulled in excess of 500 lbs. on 14 gauge, without
much stretching. I will ask around work for more
information on this, or just put some on a machine and find
out the tensile strength.
I can't help you with the velocity factor of 12 gauge.
The THHN designation is strictly the insulation type. It
has nothing to do with the conductor itself.
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Rick Andren n9thc@foxvalley.net andrenr@ul.com
From: "Rick Andren" <n9thc@FoxValley.net>
It turns out that Und. Labs. has no requiements for the
actual conductor, in this case, 12 AWG. Their only concern
with tensile strength is the insulation.
Rick Andren n9thc@foxvalley.net andrenr@ul.com
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From: Garry & Yelena <ni6t@best.com>
I will give you a pragmatic and relatively non-technical
response--that stuff was not intended to be under tension,
is quite soft, and will break. When my inverted L broke, it
cost a small fortune to get the tree climbers up to retrieve
the end--obliterating any savings.
Wire is the last thing to scrimp on, unless it will NOT be
under tension. -- Garry Shapiro, NI6T
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From: Bill Bosler <wbosler@bellatlantic.net>
I've been making wire antennas out of THHN wire for years.
Mostly #12 and some #10. We have it around the shop in 1000'
spools. Also, every time I go to the scrap yard I look for
spools of it. You can buy it real cheap.
Never had any problems with stretching and it weathers real
well.
I have a 160 inverted L that's been up for years and several
40 meter antennas. I use it for radials, field day antennas
and any sort of temporary antenna I want to throw up in the
air. Bill Bosler - WF3M
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From: Brian McGinness <bmcginness@wirelessinc.com>
I had THHN on my 160m 2-el inv-L array, and after a couple
years it started to deteriorate. I think the UV got it.
I would suggest the stuff they call "#13 poly copperweld"
that RF products sells. It is very very very tough. My issue
with THHN is not it's electrical characteristics, but it's
eventual deterioration. The poly stuff is much tougher.
Brian N3OC
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From: "Healy, Rus" <RHealy@mdsroc.com>
I use #14 THHN extensively. (I probably have 2000 or 3000
feet of the stuff strung around the place). I worried about
stretch, but have never experienced enough to make a
noticeable difference. Probably my best example is an 80-
meter dipole at 65 feet, strung between two big trees, with
an RG-8 feed line. The antenna is supported at the center
and the ends, and it's pretty much horizontal. When the wind
really gets ripping (we had 75-mi/h winds three times last
winter), the antenna gets s-t-r-e-t-c-h-e-d big time! It
actually broke once--about 10 feet from the feed point. But
until then I saw no difference in its resonance over time
and stretching.
As for the dielectric strength, I wouldn't worry about that.
The only time it's a factor is when the wire is touching
something--and that's not a desirable situation! If it's of
any value, most of this wire has a breakdown rating of 600 V
RMS (presumably at 60 Hz).
The velocity factor is a big question mark. I believe it's
between 95 and 97%. The trouble is, you have to make two
antennas--one of #12 THHN and one of #12 copper, resonate
them both at the same frequency in the same position, and
measure the physical difference to tell for sure. I'm not
motivated to do this at low HF frequencies! Maybe at 10
meters . . .some day.
Dunno about a Web page, but I'd be interested in the URL if
you find one. -- Rus, NJ2L
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From: bschwerdlin@hlb.com (Bob Schwerdlin)
I've always used solid THHN. I don't know if it would be
any different results for stranded wire. I don't think it
would matter.... Bob, WG9L
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From: Phil Lefever <plefever@isd.net>
Subject: Re: [CQ-Contest] THHN Wire
Unfortunatly I don't have the specific info you are
searching but I have been building antennas from THHN for
awhile now.
I haven't had any problems with breakage or stretch but I
haven't built an antenna yet that had to support it's
feedline. (Inv V's, loops, Inv L's).
The insulation holds up to the weather well. My 40m antenna
has been up for 4 years now and it still looks like new.
I have used both AWG 12 and 14 and the only effects I have
noticed are a small (approx 5%) reduction in overall tuned
antenna length.
Phil Lefever - KB0NES kb0nes@tcrc.org plefever@isd.net
Burnsville,MN
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From: Pete Soper <psoper@encore.com>
Just a quick followup.
Brian McGinness <bmcginness@wirelessinc.com> wrote:
> I would suggest the stuff they call "#13 poly copperweld"
> that RF products sells. It is very very very tough. My
issue
I have an antenna made out of this stuff too. It's VERY VERY
strong and the insulation seems completely impervious to
whether after the first year. However, it's more painful to
use as it has a strong memory and tries to coil itself up at
the first opportunity. But there's also that danged velocity
factor...Pete KS4XG
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From: Kevin Schmidt <w9cf@ptolemy.la.asu.edu>
I have some Home Depot 14 Gauge solid THHN with black
insulation which I just spent 15 minutes measuring and then
doing a little calculation. For what it's worth here are
the results. I cut a short piece (26.6 cm), covered it with
aluminum foil, and measured the admittance between the wire
and foil with an old GR821A. I got C = 7
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8.5 pF and an
impedance of Z = 23 -j 578 ohms. I then measured the
insulation diameter and the bare wire diameter to be 0.108
inches and 0.066 inches with a dial indicator rigged up as a
thickness gauge. According to the wire tables #14 is 0.064
inches in diameter so either my indicator is off or the wire
at Home Depot is not high precision. Anyway the calculate
capacitance should be eps*29.1 pF which makes eps = 2.7 (For
comparison, teflon is 2.1 and I don't know what nylon is). I
was surprised by the low Q = 25 of this capacitor.
I have a modified moment method code that I can use to model
thin dielectric and/or magnetic coatings on antennas that is
probably accurate enough for most HF designs. It uses the
approximate method of Richmond and Newman, Radio Science,
11, 13-20 (1976), which I slightly generalized to magnetic
and lossy coatings. The code predicts that on both 80 and
160 meters, this dielectric coating causes the resonant
length to be 2 percent shorter and the resonant input
resistance in free space decreases about 2 ohms.
Kevin Schmidt w9cf@ptolemy.la.asu.edu
Department of Physics and Astronomy
Arizona State University, Tempe, AZ 85287-1504
(602) 965-8240
(602) 965-7954 (FAX)
-- end of file --From k1vr
From: k1vr
Full-Name: Fred Hopengarten
To: oweng@oweng.com
Subject: w7ni@teleport.com (Stan Griffiths): Re: [TowerTalk] Rohn phone
number
X-Status: Unsent
From:
Fred Hopengarten K1VR 781/259-0088
Six Willarch Road
Lincoln, MA 01773-5105
permanent e-mail address: fhopengarten@mba1972.hbs.edu
Another justification for people to buy our program when it comes out!
--------- Begin forwarded message ----------
From: w7ni@teleport.com (Stan Griffiths)
To: Pete Brunet <brunet@us.ibm.com>
Cc: towertalk@contesting.com
Subject: Re: [TowerTalk] Rohn phone number
Message-ID: <199803270721.XAA26428@mail1.teleport.com>
>Steve, Here are my unanswered questions. These are related to Rohn 45.
>
>Since Rohn's wind loads are substantially higher for a house bracketed
70'
>tower (at 56' and 28') (32 sq. ft. at 70 mph) than a tower with their
two
>recommended guys at 35' and 65' (9.5 sq. ft. at 70 mph assuming tower
has 8 sq.
>ft. for sidearms and 6 transmission lines coming up the sides), how much
extra
>wind load, if any, would be gained by using 3 guys at 23' increments?
>
>Concerning subtracting 8 sq. ft. for the side arms, is that 8 sq. ft. a
round
>member spec or a flat member spec? (If it is the former that would be
>equivalent to 4.8 sq. ft. of antenna wind load.)
>
>The Rohn notes say that the tower design includes a 1/2" and 7/8"
transmission
>line on each of the three faces. Ours will only have two (probably .5
inch) so
>it appears that I can also subtract the surface area of the missing 4
lines (1
>1/2" line and 3 7/8" lines), i.e. ( 70' * (1/2 + 3 * 7/8) / 12 ) * .6 )
= 10.9
>sq.ft. But that assumes that wind load of the coax along the side is
the same
>as the wind load for an antenna at the top, which probably isn't
equivalent.
>How much is the right amount, if any, to subtract for the unused coax?
>
>Thanks, Pete ws4g
Hi Pete,
I think Rohn has covered your situation very well on the last page in my
catalog. This is the green page titled "Rohn Product Services
Available".
They offer a service called "Product review of non-catalog towers with
simaltaneous product review for optional loads". Your tower is clearly
"non-catalog" since you plan to put guys in places not shown in the Rohn
catalog. The price for this service is $3,000 (minimum) per tower plus
$300
per hour. It is all right there in the Rohn catalog.
I suspect they will take a rather dim view of a request from you to get
this
information for free. It would be cheaper for them to give you a free
tower
. . . With Rohn wanting this kind of cash for the answers you crave, how
good can free answers you get on the tower reflector be? What I am
saying
is, anyone who has the skill to really answer you with the kind of
expertise
I would trust is out there selling that skill for big
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Get completely free e-mail from Juno at http://www.juno.com
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bucks and not
giving
it away for free here. However, if you are willing to receive some
educated
guesses with no guarentees, you will get some good advice. You will also
get some bad advice. Knowing the difference is the real trick . . . and
really requires an engineering degree plus a lot of experience working in
the field.
The average person is simply not equipped to design a safe system like
the
one you describe. Most of us try to over-build it and still take some
chances . . . Sometimes our towers crash. Sometimes we get hurt.
Usually,
we are lucky. Minimizing the risk is expensive.
I believe the reason you did not get any answers to your original
questions
is that you posed a very complex engineering problem no one here is
equipped
to deal with thoroughly (for free at least).
Seriously, I would visit as many sites as I could with towers similar to
the
one you propose, including antenna loads. I would ask LOTS of questions
of
the owners of those towers like the following:
1. How long have these towers been up with these loads on them?
2. Who installed it and can I ask questions of him?
3. Was the system designed by a professionsal engineer?
4. Can I obtain a copy of the engineering documents and calculations?
5. Ask dozens of detailed questions about the guys anchors, guy wire
material, turnbuckles, etc.
6. Have these tower endured any heavy winds? How heavy? How many
times?
You will then have a good idea of what works in your area. If you design
stronger (in all respects) than what you have seen, you should be OK.
Good luck on your project. Be careful.
Stan w7ni@teleport.com
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--------- End forwarded message ----------
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