What would 1000 Watts HF do if you touched an antenna?
StarGazer
Pit Stop
"StarGazer" <p...@capnet.com> wrote in message
news:3D0AC392...@capnet.com...
> What would 1000 Watts HF do if you touched an antenna?
What part of the antenna are you touching ? the tip or the base?
Adam
"StarGazer" <p...@capnet.com> schreef in bericht
news:3D0AC392...@capnet.com...
> What would 1000 Watts HF do if you touched an antenna?
You would probably dance the boogie woogie without taking lessons :-)
As a ham you know that the radiation pattern around an antenna has maximum
'U' and maximum 'I' at certain spots. If you touch it at the 'wrong' spot
you have a chance to get high current shock or burn your skin or even get
killed. I wouldn't recommend taking the risk. Besides that, the magnetic
field would be much higher near your body than recommended by the standards
of the World Health Organization.
If you would touch an antenna with even much lower power you could already
get injuries. If you use a magnetic loop, even the RF power of 10 Watts
could cause injuries. Read the manual of MFJ about magnetic loops. It's in
Acrobat-pdf on their website.
73s, Adam
'Doc
StarGazer,
It would probably give you a white mark across
whatever part of your body touched the antenna. It
would also remind you not to do that again...
'Doc
Dick Carroll
> What would 1000 Watts HF do if you touched an antenna?
Guaranteed you don't want to find out by direct
experimentation. RF makes neat little DEEP burn holes in
your body.
Dick
Richard Harrison
"What would 1000 watts HF do if you touched the antenna?"
It would likely burn you. Nothing else to you.
Due to "skin effect", negligible r-f current penetrates deeply into your
body.
Many milliamps are usually needed through the heart to stop its beating
and there is almost no danger of electrocution.
1000 watts at 30 ohms is about 173 volts. Momentary contact at a peak of
245 volts at 50/60 Hz won`t kill most people.
Low d-c voltages aren`t shocking to most people under most conditions.
Dry skin resistance is 1000`s of ohms, but but drops in the blink of an
eye. This phenomenon is used for lie detection. Sweat brings skin
resistance down. I`ve read of electrocution at 30 volts!
I`ve never been shocked by 30 volts and I`ve survived KV d-c contacts,
but they hurt and sometimes burned.
I`ve survived 10`s of KV r-f contacts. It didn`t feel like a
low-frequency shock at all. On the roof of a shortwave broadcast plant,
I bumped an ear into an energized 600-ohm transmission line carrying 50
KW. I heard something like: "Radio Volna Europa. Vlos Volna Polska". I
think that translates into "Radio Free Europe. The voice of Free
Poland", but I don`t speak polish. Whatever it was it was loud and right
in my ear. That plasma really talks! My ear was really hot. It was
redder and continued to redden for hours. Then it started to darken
until it looked like carbon. After several weeks, the surface flaked
away. Skin and flesh returned to normal leaving no scars.
I`ve had many r-f burns from lower powers, watts to kilowatts. None
shocked. They just burnt. The burns were usually sorer than the 50-KW
burn. But most were on or around the hands which have more nerve endings
to register pain than does the ear.
Best regards, Richard Harrison, KB5WZI
Peter O. Brackett
--Peter K1PO
Indialantic By-the-Sea, FL.
"StarGazer" <p...@capnet.com> wrote in message
news:3D0AC392...@capnet.com...
Richard Clark
(Richard Harrison) wrote:
>
>Many milliamps are usually needed through the heart to stop its beating
>and there is almost no danger of electrocution.
>
>1000 watts at 30 ohms is about 173 volts. Momentary contact at a peak of
>245 volts at 50/60 Hz won`t kill most people.
>
>Low d-c voltages aren`t shocking to most people under most conditions.
>Dry skin resistance is 1000`s of ohms, but but drops in the blink of an
>eye. This phenomenon is used for lie detection. Sweat brings skin
>resistance down. I`ve read of electrocution at 30 volts!
>
Hi Richard,
I took my ohm meter and found no less than 1.5 MOhms hand-to-hand.
Yesterday in hotter weather, I would've speculated at 10,000 Ohms
instead.
Resistance is very much to the matter, as it is current, not voltage,
that kills.
Skin is a resistive sheathe covering a poor (dissipative) conductor
and it has a grid work of openings (pores) allowing for conduction
through many parallel paths penetrating the high resistant layer.
Lethal current through the muscle, bone, and nervous system is
generally figured from 20 mA up. 10 mA is painful (to personal
tolerance) and less so toward 5 mA below which it becomes a sensation.
Lethality can come by surprise. A 20 mA lethal current is not common,
but given the right conditions.... One contributor to this surprise
is found in the state of the current. DC causes muscular rigidity,
whereas AC causes muscular fibrillation.
With a DC shock you may be forced by the current to grip the
conductor. With AC (so Geo. Westinghouse may have retorted to
Edison), the muscles quiver and the grip relaxes allowing you to break
free of the contact (you might think of it as chattering loose).
Edison would've no doubt hammered back that AC fibrillation of the
muscles also causes the pores to sweat (pumping action here) causing
the skin resistance to plummet - and guess (the surprise) what?
AC in the realm of RF does not seem likely to lead to fibrillation,
but it will feel no less painful (and my experience is more painful
than a flame burn).
73's
Richard Clark, KB7QHC
Jack Louthan
a pencil and draw arcs at the ends of antennas attached to
transmitters running about 100 watts. You can get an arc about an inch
long with 100 watts. I remember also getting burns on my
fingers...like Doc says the burns had a distinctive white color. It
was also fun to hold a flourescent bulb near the antenna and watch it
light up.
This was with 100 watts. I'm glad I never tried it with 1000 watts. I
wouldn't even think of doing anything like that now!
Reg Edwards
No more than a red-hot needle being stuck 2 millimetres into the end of your
index finger. If it was of any real danger
you Americans would have incorporated it into an electric chair and tested
it on a circus elephant. ;o)
---
Reg.
Ron Mathis
> What would 1000 Watts HF do if you touched an antenna?
Considering the voltage generally used and the possible current, it
could and most probably would kill you. That is why we keep antennas
above the reach of those that do not understand.
R Mathis N1SWK
Richard Harrison
"I`m glad I never tried it with 1000 watts."
Current divides. As Yogi Berra says, when it comes to a fork in the
road, it takes it. How much goes each way depends on the relative
impedances.
The impedance of an antenna depends on its length in terms of
wavelength. It also varies with location along the antenna due to
reflection from the open end of the antenna in most cases.
If you contact an antenna, you represent the alternate path which is a
"fork in the road". How much current you receive depends on the
impedance of the antenna at the contact point and how that compares with
your impedance.. How much you and the antenna get depend on how much is
available.
I`ve told of the broadcast stations sharing a common tower where I
worked in 1949. That tower was more than a 1/4-wave for the 950 KHz
station, and almost 1/2 wave for the 1320 KHz station. We periodically
opened shorting switches across the r-f antenna ammeters for both
stations to record their readings. To avoid r-f burns from the switch
handles attached to the extremely high voltages on the switch blades, we
used home made hot sticks to operate the switches. A hot stick was a
bent nail in any convenient stick. These had to be replaced often, as a
carbonized trail burned its way from the nail in one end of the stick
toweards the operator`s hand around the other end of the stick. During
switch operations, the sparks really flew in the gultch burnt in the hot
stick. As long as the operator stayed away from the sparks in the hot
stick, he didn`t get burnt, but it was an ever present threat.
In those days, people jumped on and off hot (operating) tower antennas,
to change lamps and perform other maintenance. I`ve done it too.
Paolo Emanuelli IK1QHB
> > What would 1000 Watts HF do if you touched an antenna?
>
> Guaranteed you don't want to find out by direct
> experimentation. RF makes neat little DEEP burn holes in
> your body.
......tattooo?????????
Paul IK1QHB
David G. Nagel
the peak voltage point you will get a good shock. If you touch the
current peak point you will get the afore mentioned burns.
It's kind of like sticking your tongue to a very cold pipe.
Dave WD9BDZ
Mike Coslo
Richard Harrison wrote:
<a whole bunch of interesting stuff snipped>
> In those days, people jumped on and off hot (operating) tower antennas,
> to change lamps and perform other maintenance. I`ve done it too.
Now you have me interested, Richard! What were the techniques of working
on a hot tower?
- Mike KB3EIA -
Dick Carroll
> Actually it would depend on where you touched the antenna. If you touch
> the peak voltage point you will get a good shock. If you touch the
> current peak point you will get the afore mentioned burns.
> It's kind of like sticking your tongue to a very cold pipe.
>
I don't think so....when you touch an antenna you may fundamentally change
it into something with an impedence that can be very different from what it
was before you touch it. This can change the voltage and current nodes. You
can't know just how.
>
> Dave WD9BDZ
>
> Paolo Emanuelli IK1QHB wrote:
> >>>What would 1000 Watts HF do if you touched an antenna?
> >>
> >>Guaranteed you don't want to find out by direct
> >>experimentation. RF makes neat little DEEP burn holes in
> >>your body.
> >
> >
> > ......tattooo?????????
> >
A DEEP one.
Tom W8JI
wrote:
>Actually it would depend on where you touched the antenna. If you touch
>the peak voltage point you will get a good shock. If you touch the
>current peak point you will get the afore mentioned burns.
>It's kind of like sticking your tongue to a very cold pipe.
Not really.
The burn AND shock you get is directly related to the voltage.
Remember your body and the connection point to your body has a modest
impedance, and it takes voltage to force current into you.
So, as long as you are a small part of the overall system load (which
you usually are), you will get a worse and worse burn and/or shock as
the VOLTAGE at the point you touch increases.
As frequency increases, shocks become less noticable and burns become
more problematic.
If the frequency is low and voltage at that point is low, you can hang
right on a conductor carrying hundreds of amperes without a burn or
shock. I've moved from wooden ladders to AM BC towers carrying many
kilowatts without feeling or noticing anything unusual or harmful.
73 Tom
Richard Harrison
"What were the techniques of working on hot towers?"
Tom, W8JI gave an answer. I don`t recall having a wooden ladder, but
that would be an excellent technique. You don`t want to be a bridge
across the base insulator. Dismounting is easy. You just jump to the
ground from a low altitude. Once you`ve climbed onto the tower, you
wouldn`t know if the power were on or off.
There were items to service and a desire to minimize carrier
interruptions. We had an FM antenna on one of the towers, r-f current
and phase sampling loops, and tower lighting on all towers.
Richard Harrison
"As frequency increases, shocks become less noticeable and burns become
more problematic."
I agree with the generalization but there are exceptions. As frequency
increases "skin effect" reduces body pennetration and the electric
shock. Contact with 50/60 Hz usually penetrates and evokes reaction.But
high volts at 50/60 Hz can really blister.We had a laborer excavating
for an antenna switching system who hit a 7 KV cable feeding 50 Hz to
one of the transmitters. The pick-axe was severely pitted and the
laborer was shocked but not severely injured except for burns from the
flash. It was that darn plasma again.
At r-f, my contact with high voltage burnt only my ear which came in
contact. At 50 Hz, the laborer`s contact burnt both his arms and legs.
Fortunately, he recovered completely with no scars.
J. Harvey, VE1BLL
> "What were the techniques of working on hot towers?"
"Richard Harrison"
> Tom, W8JI gave an answer. I don`t recall having a
> wooden ladder, but that would be an excellent technique.
> You don`t want to be a bridge across the base insulator.
> Dismounting is easy. You just jump to the ground from a
> low altitude. Once you`ve climbed onto the tower, you
> wouldn`t know if the power were on or off.
> <snip>
The workers that maintain very high voltage electric power lines use a small
helicopter and a suspended basket. They wear a 'chain mail' woven metal
suit. As the basket approaches the cable, they use a 'grounded' (to the
basket) conductive rod to draw a huge arc (several feet in length) to
equalize the voltages. And then they clamber out of the basket and onto the
cables.
I assume that they leave their wallets (credit cards) and wrist watches back
at the office...
CAM
> The workers that maintain very high voltage electric power lines use a small
> helicopter and a suspended basket. They wear a 'chain mail' woven metal
> suit. As the basket approaches the cable, they use a 'grounded' (to the
> basket) conductive rod to draw a huge arc (several feet in length) to
> equalize the voltages. And then they clamber out of the basket and onto the
> cables.
>
> I assume that they leave their wallets (credit cards) and wrist watches back
> at the office...
... along with their common sense. :-)
--
cheers, CAM http://www.qsl.net/w5dxp
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DL7JSK
my magloop and it felt VERY hot - with abt. 25 W
73
Tom
"StarGazer" <p...@capnet.com> schrieb im Newsbeitrag
news:3D0AC392...@capnet.com...
vhfradiobuff
I think the appropriate reply to this question is: "Why the hell do
you want to know!?" :)
Tom
news:5e5fccab.02061...@posting.google.com...
I think he wants to know if he has to order a coffin before....
T.
Heinz W. Wiggeshoff
> "J. Harvey, VE1BLL" wrote:
>> The workers that maintain very high voltage electric power lines use a small
>> helicopter and a suspended basket. They wear a 'chain mail' woven metal
>> suit. As the basket approaches the cable, they use a 'grounded' (to the
>> basket) conductive rod to draw a huge arc (several feet in length) to
>> equalize the voltages. And then they clamber out of the basket and onto the
>> cables.
Hmm. I've never seen this, but it does mimic the birds who land on
high tension wires and live to fly away - provided they don't short out.
Yet I don't see any birds on the 100,000 V + lines, few on the 3 kV lines.
They seem to prefer the 220 V lines for perching and shitting on cars and
pedestrians. It must have something to do with coronal discharge ruffling
their feathers.
>>
>> I assume that they leave their wallets (credit cards) and wrist watches back
>> at the office...
And those with heart pacemakers need not apply.
>
> ... along with their common sense. :-)
Helicopters and power lines - there's a life limiting combination.
Irv Finkleman
Little Willy played with matches...
--
Diagnosed Type II Diabetes March 5 2001
Beating it with diet and exercise!
297/215/210 (to be revised lower)
58"/43"(!)/44" (already lower too!)
--------------------
Visit my FINALLY UPDATED website at
http://members.shaw.ca/finkirv/
--------------------
Irv Finkleman,
Grampa/Ex-Navy/Old Fart/Ham Radio VE6BP
Calgary, Alberta, Canada
Richard Harrison
"The workers that maintain very high voltage electric power lines use a
small helicopter and a suspended basket."
Birds landing on 100 KW r-f transmission lines aren`t so fortunate. They
don`t survive.
100 KW, 100% modulated, is 150 KW.
150 KW across 600 ohms is sq.rt. 90 million.
Sq. rt. 90 million = 9487 volts.
Peak voltage = 13,414 volts, not very high as compared with 50/60 Hz, or
d-c transmission voltages.
Birds landing on these 600-ohm transmission lines instantly disappeared,
none the less, in puffs of flame, steam, and smoke. All that remained to
mark their visit were claws clenching the the cable. No body, feathers,
nothing hit the ground. The birds were simply vaporized.
M.J.Powell
Richard Harrison <richard...@webtv.net> writes
Did they put one foot on each cable?
Mike
--
M.J.Powell
DL7JSK
don't have any lines with 600 ohm here (afaik).And I didn't see any birds
turning into smoke and steam when landing on high voltage lines or on my
antenna (with VERY small 100 W)
73
Tom
"Richard Harrison" <richard...@webtv.net> schrieb im Newsbeitrag
news:4887-3D0...@storefull-2395.public.lawson.webtv.net...
Jerry Oxendine
StarGazer <p...@capnet.com> wrote in message
news:3D0AC392...@capnet.com...
> What would 1000 Watts HF do if you touched an antenna?
I'd pay atttention to the fellas on here and DON'T do it! I played a trick
on a
biker in my younger days who took a dislike to my mobile HF antenna. Back
in
the late 60s, I was running some AM gear in the mobile (about 75 watts). I
pulled
into a Shoney's (Azar's for you 9-landers) and into the rear of the
drive-in. There were
some bikers parked in the shopping center lot behind me observing the girls
cruising
thru the drive-in. It had just finished a thunder shower, and the pavement
was wet and
steamy. I rolled my window down to order a meal when I overheard one of
those
ruffians in tattoos and leathers say, "hey, look at that guy over there with
the funky antenna on the car. I'm a-gonna go over there, break it off, and
dare the SOB to do
anything about it". I thought, "Hmmmmm, I don't know if you will or not."
So I turned
on my transmitter filaments, and observed the biker approaching from my rear
view.
He attempted to sneak up so as not to attract attention. I keyed the mike
(I hadn't cut
off the engine to keep the a/c running. The dynamotor spooled up, and I
watched the
guy creep up as I pretended not to notice. He slipped his fingers around
the whip about
halfway up the whip above the coil. Remember: everything, including the
antenna, is very WET. Had he grabbed the antenna firmly, it might not have
done anything but get
very warm so he would've let go. But, he slowly closed his fingers around
the whip, and
I saw in the mirror a distinct little blue spark arc across about 1/8" or so
to his finger and
thumb! He yelped, snatched his hand back slinging it, and sucking his
thumb, cursing as
he returned to his bike! "DAMN!" DON'T TOUCH THAT B*******'S CAR---THAT
SOB'S ELECTRIFIED!!" I had had smart punks threaten to tear up my antennas
before, but the word must've gotten out amongst the young toughs of the day
(I was only 21) 'cause after that, no one ever offered to touch my car!
LOL! It was SO funny to watch that biker's face as he recoiled in shock
(pun intended).
Jerry
K4KWH
>
Richard Harrison
"Did they put one foot on each cable?"
The old story: "Little old lady asks the motorman if putting her foot on
a streetcar rail will shock? Motorman replies: "Only if she puts her
other foot on the overhead wire."
RF doesn`t require such a spread. The birds` feet usually grip only one
of the wires in many pairs indicating near perfect two-point final
landings. Never watched a bird land on the wire, only heard the sound
and turned to see the smoke, steam, and clenched feet gripping the wire.
Richard Harrison
"What transmission lines are you talking about?"
Shortwave broadcasters use 600-ohm transmission lines between
transmitters and antennas for lowest loss. High voltage and low current
are needed for low current squared loss just as in 50/60 Hz
transmission.
Sky-wave propagation changes with the daily solar radiation cycle, so
shortwave broadcasters change antennas during the 24-hour cycle to fit
the frequency predictions for the intended paths. This requires
switching.
Some of our lines used wire as small as 6 AWG, to be accepted by Brown
Bovari Corporation antenna switches. Birds could get their feet around 6
AWG wire. If the line was hot with 100 KW, the bird was history when it
hit the wire.
In Germany you have many kilometers of identical transmission lines,
switches, and bird feet. I`ve been there, seen for myself, and could
take you to the sites.
Heinz W. Wiggeshoff
>
...
> none the less, in puffs of flame, steam, and smoke. All that remained to
> mark their visit were claws clenching the the cable. No body, feathers,
> nothing hit the ground. The birds were simply vaporized.
Next stop: Kentucky Fried Chicken. Tastes less gamey too.
Richard Harrison
"Some of our lines used wire as small as 6 AWG, to be accepted by Brown
Bovari Corporation antenna switches."
I fat fingered Brown Boveri. Saw it after the posting appeared. It is
now ABB ASEA Brown Boveri, and they no longer make the antenna switches
we used in Deutschland or anywhere else. Sad. It was a nice design.
Peter O. Brackett
> Helicopters and power lines - there's a life limiting combination.
I believe that it is fairly common to use helicopters and trained linemen to
do live power line work these days.
In fact, I just passed one in action about two weeks ago while driving in
central Florida, just South of Orlando.
The helicopter and the suspended lineman were working on an FPL power line
about 50 yards from US 192 on which I was driving on at the time.
--Peter K1PO
Indialantic By-the-Sea, FL.
M.J.Powell
Richard Harrison <richard...@webtv.net> writes
>Tom, DL7JSK wrote:
>"What transmission lines are you talking about?"
>
>Shortwave broadcasters use 600-ohm transmission lines between
>transmitters and antennas for lowest loss. High voltage and low current
>are needed for low current squared loss just as in 50/60 Hz
>transmission.
Last time I went round a BBC SW station I was told that they used 50 ohm
skeleton coax from the TX to the ATU.
Mike
--
M.J.Powell
M.J.Powell
Richard Harrison <richard...@webtv.net> writes
Well, I can't image the cause, no current path except for a small
capacitative charging current which I would have thought wouldn't be
enough to fry the bird.
Mike
--
M.J.Powell
Richard Harrison
"Last time I went round a BBC SW station I was told that they used 50
50 years ago I worked in a 790 KHz station which used 50-ohm skeleton
coax. The 4-wire outer conductor was held in place with metal U-supports
atop metal posts in the earth. The center conductor was a pair of
paralleled wires held in place in the center of the outer conductor by
isulators atop the support posts. This is one of several such skeletal
coax designs and it worked very well with only slight influence of foul
weather.
Problem of 50-ohm coax is wire size. 100 KW at 50 ohms is 44.7 amps. 100
KW at 600 ohms is 13 amps. Loss is current squared times the resistance.
The current ratio above is about 3.44, so the loss ratio for a given
copper resistance produces 11.8 times the loss in the 50-ohm line as in
the 600-ohm line as a rough example.
On a medium wave frequency you have usually only one or two patterns.
Some stations use one pattern 24 hours while others are required to
switch between daytime and nighttime patterns. In either case, there are
a limited number of towers and one transmission line per tower.
Parasitic arrays are almost non-existent.
At shortwave frequencies, a broadcaster typically has many more antennas
than transmitters because separate antennas for each band are more
specific for a given target area coverage and the broadcaster has to
band hop during the broadcast day to accomodate propagation
expectations. Also, unlike the medium wave broadcaster with a single
target, the shortwave broadcaster usually is assigned many targets and
must have antennas aimed at each target.
The economics of transmission lines looms much larger to the usual
shortwave broadcaster than it does to the usual medium wave broadcaster
in most instances.
Fred Hambrecht
drooping dipole with a pencil. (just don't get your fingers on the metal
eraser part) and you could hear the modulation in the arc.
Probably not the brightest thing I ever did, but it impressed the hell out f
the neighbors.
"vhfradiobuff" <vhfrad...@aol.com> wrote in message
news:5e5fccab.02061...@posting.google.com...
Richard Harrison
"Well, I can`t imagine the cause, no current path except for the small
capacitive charging current---."
True. There wasn`t any obvious prevention and it wasn`t big trouble for
us so we ignored it.
The flash had to begin with a small spark, no doubt provided by the bird
getting very near the wire. Lightning may begin with a small spark and a
plasma trail which grows.
Our 600-ohm lines seldom flashed over line to line or line to anything
else. We had arc gaps with much closer spacing than the line spacing.
Even so, we had rare line to line flashes triggered by something but
usually we were ignorant of the cause. It may have been the birds.
Transmitter protection circuits momentarily killed the transmitters on
overloads and restarted them several times before ending attempts to
restart. I wasn`t curious enough to try to correlate bird flashes I`d
seen with carrier interruption records.
The thing I`m certain of is the many pairs of bird feet clenched on the
wires with no trace of the bird.
K7JEB
> 50 years ago I worked in a 790 KHz station which used 50-ohm skeleton
> coax. The 4-wire outer conductor was held in place with metal U-supports
> atop metal posts in the earth. The center conductor was a pair of
> paralleled wires held in place in the center of the outer conductor by
> isulators atop the support posts....
If you crank through the formulas for this type of line,
I think you'll find that the characteristic impedance
is closer to 200 ohms.
--
Jim Bromley, K7JEB k7jeb @ arrl.net
Glendale, Arizona
Richard Harrison
"If you crank through the formulas for this type of line, I think you`ll
Yes, I`m sure that`s correct. It requires too-close spacing even with
large wire to get down to the 50-ohm impedance I quoted. I was wrong. Ed
Laport has calculated the impedance of a popular 6-wire line of this
skeletal coax type. This is just one of about a dozen different lines of
this general type Ed has calculated and presents. For this 6-wire line
Ed calculates a Zo of 231 ohms.
That 790 KHz station used a 4-tower directional array. Never mind what
impedance individual lines presented, after tuning and phasing, their
combined transmitter load was 50 ohms. That was what the transmitter was
specified to serve and where its performance was guaranteed. The station
was licensed for a specified number of r-f amps into the 50-ohm "common
point" impedance (a resistance). An ammeter at that point constantly
displayed the common point current and was regularly read and recorded
during hiatuses in modulation.
CAM
>
> Jim Bromley, K7JEB wrote:
> > "If you crank through the formulas for this type of line, I think you`ll
> > find the characteristic impedance is closer to 200 ohms."
>
> Yes, I`m sure that`s correct.
I've known Jim for more than a dozen years. I have never known him to be
wrong about antennas and transmission lines. The only time he was incorrect
was the time when he thought he was incorrect.
Alan Fowler
>> Richard Harrison, KB5WZI:
>
>> 50 years ago I worked in a 790 KHz station which used 50-ohm skeleton
>> coax. The 4-wire outer conductor was held in place with metal U-supports
>> atop metal posts in the earth. The center conductor was a pair of
>> paralleled wires held in place in the center of the outer conductor by
>> isulators atop the support posts....
>
>If you crank through the formulas for this type of line,
>I think you'll find that the characteristic impedance
>is closer to 200 ohms.
I agree. We used these (six wire) transmission line
to connect 50 kW transmitters to a 5/8 wavelength vertical
aerial for the Australian "National Broadcasting Service."
3AR (620kHz ) and 3LO (770lHz fed into a common aerial.
The aerial matching unit had to feed power to the aerial
with minimum loss, and at the same time prevent any
significant power being fed back to the other transmitter.
One of the problems with the six wire line is that a
significant amount (about 20% if I remember correctly) of
the return current flows in the earth instead of the outer
four wires.
We used about 6 wires (200 lb copper) buried under
the line, and bonded to the metal poles which were also
bonded to the outer four wires to reduce losses in the
earth.
Alan
Fractenna
> We used about 6 wires (200 lb copper) buried under
>the line, and bonded to the metal poles which were also
>bonded to the outer four wires to reduce losses in the
>earth.
>
> Alan
>
How well did that hold up against corrosion (and more ohmic loss)?
73
Chip N1IR
K7JEB
Alan Fowler:
> One of the problems with the six wire line is that a
> significant amount (about 20% if I remember correctly) of
> the return current flows in the earth instead of the outer
> four wires.
The only installation using this type of line I saw was at
XELO (now XEROK), 800 KHz, in Cuidad Juarez, Chihuahua,
Mexico. I was impressed with the intense E field that
existed underneath and to either side of the transmission
line (XELO ran 150 KW in those days). It was strong
enough to light a 40-watt fluorescent tube to full
brilliance 8 feet from the line.
> We used about 6 wires (200 lb copper) buried under
> the line, and bonded to the metal poles which were also
> bonded to the outer four wires to reduce losses in the
> earth.
I guess there's something to be said for 6-inch rigid
coax after all.
Alan Fowler
>
>Alan Fowler:
>> One of the problems with the six wire line is that a
>> significant amount (about 20% if I remember correctly) of
>> the return current flows in the earth instead of the outer
>> four wires.
>
>The only installation using this type of line I saw was at
>XELO (now XEROK), 800 KHz, in Cuidad Juarez, Chihuahua,
>Mexico. I was impressed with the intense E field that
>existed underneath and to either side of the transmission
>line (XELO ran 150 KW in those days). It was strong
>enough to light a 40-watt fluorescent tube to full
>brilliance 8 feet from the line.
Never saw any evidence of strong field from our
lines, but didn't go looking for it either.
>
>> We used about 6 wires (200 lb copper) buried under
>> the line, and bonded to the metal poles which were also
>> bonded to the outer four wires to reduce losses in the
>> earth.
>
>I guess there's something to be said for 6-inch rigid
>coax after all.
The six wire lines were built to replace two 3 inch
rigid co-ax lines. The co-ax was buried to protect it from
damage. Unfortunately, the soil was a heavy clay which sets
a good grip on the cable. It also moves a lot with weather
changes, large cracks open up in summer as the clay dries
our, and small cracks occurred in the outer.
Every improvement seems to bring new problems.
Alan.
Alan Fowler
There have been no problems as far as I know, but
it's about 35 years since I was last involved. The main
earth mat used the same wire and had been in use for about
25 years before I saw it. It was in good condition the,
Alan.
>
>73
>Chip N1IR
Richard Harrison
"There have been no problems as far as I know---."
We had no problems with 6-wire lines.
We could light our way at night by simply carrying almost any florescent
tube , good or bad. But, we easily met all radiation criteria,
efficiency, pattern, and null depths.
We had no dis-similar metal problems. Copper radials were buried. So
were the zinc-coated posts supporting the 6-wire lines. The outer wires
of these lines were zinc-coated too. The inner wires were copper but
they were supported on insulators. The zinc coating on the posts
outlasted the station location which has moved several times in the last
50 years.
Best rergards, Richard Harrison, KB5WZI
Richard Harrison
"We used these (six wire) transmission lines to connect 50 KW
transmitters to a 5/8 wavelength vertical aerial for the Australian
I`m impressed. In 1949 I worked in a plant where two 5KW transmitters
shared the same high tower and I have already told how sparks flew just
when we opened the ammeter shunts to read the tower currents from each
transmitter. Two 50 KW transmitters could really be hot! I suppose the
5/8-wave was at 770 KHz and not 620 KHz, so as to avoid too much
high-angle radiation at 770 KHz.
We had buried coax and high-stress soil just as Alan had, but we were
lucky. It had been in place about a decade in 1949 and was used by one
of the transmitters for about 20 more years. I know of no problems. The
950 KHz station moved away long ago and relocated several times. The
1320 KHz station is still broadcasting from the same tower, but has
replaced its transmitter several times to lower its electrical bill
through higher efficiency.
In 1949 the transmitter was an RCA 5-C, which was a 250-watt transmitter
followed with a 5-KW linear amplifier. Efficiency was about 20%, if I
recall. Something like 25 KW input!
A couple of years later, both station transmitters 950 KHz, and 1320
KHz, were replaced with RCA BTA-5F`s, which were high-level, plate
modulated, and cut the power bill at least in half.
Then, Ampliphase replaced the high-level modulation to trim the power
bill even more.
Don`t know what is being used now. The big fancy plant is gone and the
property it occupied now has new buildings housing several service
businesses. The transmitter seems to be located in the dog house next to
the tower and a shack next door seems to serve as studios. That used to
be our NBC Blue Network/ABC outlet. It`s now a Spanish Language station.
They don`t need much in the way of transmission line of any type
anymore.
ziyadk...@gmail.com
Fred McKenzie
> Hi I need to know how mutch wire 14 gauge can transmit by watts from hf on my
> base yaesu ft897
223.61 Volts and 4.47 Amps RF at the feed point. Along the antenna, I
expect voltage to increase and current to decrease as you move away from
a 50 Ohm feed point.
I think a 14 gauge wire should be OK for the antenna, but DO NOT TOUCH
IT. It might burn your finger off.
But what are you really asking? I understand the FT-897 has a 100 Watt
transmitter. A 100 Watt transmitter would produce 70.71 Volts and 1.41
Amps at the 50 Ohm feed point. It might not burn your finger off, but
would cause a serious burn.
Fred
Rob
> Hi I need to know how mutch wire 14 gauge can transmit by watts from hf on my base yaesu ft897
determines the maximum current, not the maximum voltage. And watts
is current times voltage.
So when you use a higer voltage with the same current (i.e. you have
a higher antenna impedance, of course matched with a tuner) you can
use thinner wire at higher power.
Ralph Mowery
ziyadk...@gmail.com says...
> Hi I need to know how mutch wire 14 gauge can transmit by watts from hf on my base yaesu ft897
>
>
amateur radio.
The 14 wire will take over 1500 watts easy.
Any wire that is strog enough to support its self will transmit over 100
watts.
Bigtexun Tex
> What would 1000 Watts HF do if you touched an antenna?
If a kid walks up to a broadcast transmitter base where the mast is the antenna, and sees the spark gap at the base, he might be foolishly tempted to wack the gap to bang it closed. Even more foolishly use the heels of his bare palms to do it. There is a smell of burned flesh, and a surpprised kid. A couple inches of tracks under the skin up the wrists... minor pain.
John S
--
Dogs make me happy. Humans make my head hurt.
Allodoxaphobia
> On Friday, June 14, 2002 at 11:33:22 PM UTC-5, StarGazer wrote:
>> What would 1000 Watts HF do if you touched an antenna?
google groopers! ... replying to 20-year old usenet posts!