Cecil Moore wrote:

Reg Edwards wrote:

The number one reason for attenuation being higher is because the
conductor diameter is smaller and, as a consequence, its resistance is
higher.


On that we can disagree. The *number one* reason for attenuation
being higher is because, in a matched feedline, the losses are
proportional to the square of the current, and the current is
inversely proportional to the characteristic impedance of the
feedline, i.e. given #20 wire, a Zo-matched 75 ohm feedline
will have Sqrt(600/75) times the I^2*R losses of a matched 75
ohm feedline. Proof:

SQRT(100w/75) = SQRT(600/75)*SQRT(100w/600)

SQRT(100w/75)/SQRT(600/75) = SQRT(100w/600)

100w/600 = 100w/600

Given that the center conductor of RG-213 is the same size wire as
a parallel feedline, a *very* large percentage of the difference
in matched line dissipation is due to the Z0. (I don't know the
size of the center wire in RG-213 but it looks like #14 or #12.)
I don't think the RG-213 center conductor is at all smaller.

Resistivity is the 'R' in I^2R, as Reg indicated.

ac6xg

Wes Stewart wrote:
On 15 May 2005 17:59:50 -0700, "Brian Kelly" wrote:

So there are conductor *and* dielectric I=B2R
losses to consider in this discussion yes?
=20
=20
No.

.. . that's unambiguous enough . .

Whilst on the romantic subject of coaxial attenuation -

Attenuation is the number-one characteristic of all transmission
lines. From power frequencies and upwards. Yet, quantitativly, it is
the smallest parameter per mile and the most difficult to measure
accurately. An innocent observer might think it is hardly worth
bothering about.

It is inextricably mixed up with system economics. An exact knowledge
even of the temperature coefficient of attenuation is vital to
communications system design.

Around the 1950's I was involved with measurement of attenuation (and
other characteristics) of the first oceanic submarine telephone
cables. A transatlantic coaxial cable, 2000 miles long, has an overall
attenuation at 5 MHz of around 4000 decibels. The temperature
coefficient of attenuation is half of the resistance temperature
coefficient of copper which is 0.4 percent per degree C. Which was
well known to Oliver Heaviside around 1875.

Thus, a change in temperature on the ocean bottom of 0.1 degree
results in a change of 80 dB in the signal level at the far end.
Unless corrected in the repeaters (of which there were about 100) this
is enough to shift signals between the thermal noise level of an
amplifier and its overloaded cross-modulation level.

One of the cable factories was located in Southampton Docks. As cable
came off the production machinery at about 1 mile per hour, it was
coiled in giant circular concrete tanks below ground level, the same
size as an 8000-ton cable-laying ship's hold. Attenuation and other
measurements were made in the tanks by automatic testing equipment.
The cable was then loaded onto a cable ship waiting for it in the
nearby dock.

I designed a special attenuation and phase-shift tester for research
purposes. It did not incorporate an SWR meter. It did incorporate a
phase-locked-loop but it was not until several years later that I came
by chance upon a learned paper by Gruen and discovered how a PLL
really works. The equipment was all tubes. A whole mobile rack of it!
The final output meter was a moving-coil instrument with a scale
calibrated in 0.001 decibels. There were also home-brewed 0.001 dB
stepped attenuators which I had to calibrate myself.

To determine attenuation temperature coefficients in was necessary to
bring tons of ice by lorry from Billingsgate fish market in central
London. One of the concrete tanks was flooded with sea water and the
ice dumped in. It took 24 hours for the temperature to stabilise. I
spent much of the waiting time in a pub in Southampton Town. I never
knew who organised and paid for delivery of the ice which must have
been the most intricate and illegal part of the whole operation.

The data accumulated was rushed to the boffins who immediately began
designing even higher frequency oceanic systems. I was rewarded with a
pat on the back and told to keep my mouth shut. Politics were
involved somewhere.

My tester should have eventually been installed in the Science Museum,
Kensington, London. But long after the job was finished it was stolen
by some unfeeling person and cannibalised for the spare parts. There
was a BC221, straight-line frequency variable tuning capacitor built
into it. I would have liked that for myself.

Hope you enjoyed the story. From what I remember it's mostly true.
Southampton makes a change from Manchester and Leeds. The Queen Mary
was berthed not far from the Cable Ship Monarch.
----
Reg, G4FGQ

Reg Edwards wrote:

A transatlantic coaxial cable, 2000 miles long, has an overall
attenuation at 5 MHz of around 4000 decibels. . .

Just to get a little context here. . .

Years ago when I was a little bored, I determined that the ratio of the
light output from a common two cell flashlight to the entire light
output of the Sun is a mere 280 dB (10^28). So if you attenuate the Sun
by 280 dB you get the light of a flashlight beam. Well now, if you took
that flashlight beam and attenuated it again by the same amount, then
did that again, and again, 14 times altogether, you still wouldn't quite
have totaled 4000 dB. It's a staggering number, incomprehensible except
by some pretty abstract thinking. It's real, though. I remember reading
a paper long ago about transatlantic cables, and those are the numbers
they work with.

Roy Lewallen, W7EL

Reg Edwards wrote:
Hope you enjoyed the story.

That's a really enjoyable story, Reg. Thanks for sharing.
During that time I was involved in smuggling operations -
smuggling girls into my Texas A&M dorm. :-) Today, there
are girls all over the Texas A&M dorms.
--
73, Cecil http://www.qsl.net/w5dxp


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Reg Edwards wrote:
Whilst on the romantic subject of coaxial attenuation -

A follow on from Reg's story, is that (in submarine the cables with
which I was familiar), there was another grade of cable also used, a
repair cable that had about two thirds the loss of the regular cable.

It was used when repair was necessary (eg repeater failure, cable damage
from anchors , earthquakes etc). It is not possible to effect a repair
without cutting the original cable in order to get the cable to the surface.

The technique used on CS Monarch and the like, was to use a special
grapnell that caught the cable (often after many days of steaming back
and forth across the suspected cable position) and hauled it up until a
pre-determine tension was reached which activated a cutter in the
grapnell, which separated each end off on a separate hauling line. One
was buoyed off, and the CS steamed toward the other cable end until
sound cable was retrieved. It was sealed and buoyed off. They then
steamed back to the other buoy and retreived the other end, again
steaming until sound cable was found. Calculations were then done of
depth, position, losses to find how much more cable was to be removed so
that when the repair cable was inserted, the S/N into each of the
affected repeaters was sufficient to allow normal operation (these were
linear FDM or carrier telephone cables). (In some cases, so much cable
was affected that a mix of original cable and repair cable was used.)

This operation could take several days in good weather, worse in bad seas.

Owen

PS: 4000 dB sounds a lot, but when it is stated as 40dB between
repeaters it sounds more manageable.

Really, to all you guys:

There is sense, and there is non-sense here...

Never doubted you ALL had the the sense, just pleased you can enjoy a bit of
non-sense...

And, yes, the first time I found out I had to increase effective radiated
power by a factor of 4 to achieve a factor of 2 on someones S-Meter--I was
disapointed--not sure I have fully recoved from the meaning of that to this
very day--frankly, I expected more... I expect if I consulted a
psychiatrist on all this--he would, most likely, chalk it up to "penis
envy"... and that is why I have not... grin

Warmest regards,
John

"Roy Lewallen" wrote in message
...
Reg Edwards wrote:

A transatlantic coaxial cable, 2000 miles long, has an overall
attenuation at 5 MHz of around 4000 decibels. . .

Just to get a little context here. . .

Years ago when I was a little bored, I determined that the ratio of the
light output from a common two cell flashlight to the entire light output
of the Sun is a mere 280 dB (10^28). So if you attenuate the Sun by 280 dB
you get the light of a flashlight beam. Well now, if you took that
flashlight beam and attenuated it again by the same amount, then did that
again, and again, 14 times altogether, you still wouldn't quite have
totaled 4000 dB. It's a staggering number, incomprehensible except by some
pretty abstract thinking. It's real, though. I remember reading a paper
long ago about transatlantic cables, and those are the numbers they work
with.

Roy Lewallen, W7EL

Reg, G4FGQ wrote:
"A transatlantic coaxial cable, 2000 miles long, has an overall
attenuation at 5 MHz of around 4000 decibels."

That sounds reasonable as it is only 2 dB per mile. A mile is 52.8
increments of 100 feet, so that would produce about 0.038 dB/100 feet.

The lowest loss 75-ohm cable I found listed in the ARRL Antenna Book
table is 7/8-inch Hard-line at about 0.1 dB/100 feet at 5 MHz. For an
intercontinental link, you would strive for better as Reg indicated.

One problem of cable is that it has constant loss. Every cebtimeter of
length takes the same percentage loss of the remaining energy. Hence,
dB/ 100 feet.

Not so with radio in free-space. Getting rid of the wires ends their
attenuation. Loss is then due to decreased signal in a square unit of
the wavefront caused by expansion or thinning of the signal. The
"unattenuated" signal decline is 6 dB every time distance from the
source doubles, be it one mile or 1000 miles. The signal power level at
a point is 1/4 the power it had for the same area at 1/2 the distance
from the source.

We could`not communicate by wire with our space probes due to too much
loss even were the wires a practical alternative.

To cross an ocean, cable solves the problem of repeater placement. The
signal must be regenerated before it falls into noise. The repeaters are
"simply" integrated into the cable at proper intervals. The first
transatlantic cable message was sent by Queen Victoria to the American
President.

Ashore and on distant offshore platforms, I`ve puzzled why microwave was
not used instead of cable. Privacy may be one reason, but encryption,
route switching and other techniques could make theft of information
from thin air more difficult than other theft. There are always
beneficiaries of the status quo who make change difficult to impose.

In the early 1950`s, Houston`s Transcontinental Gas Pipeline Company
(Ken Lay was an officer of "Transco" before moving to Enron) built a
private microwave system from its heasdquarters to New Jersey along its
pipeline. I recall looking the new system over. It was supplied by
Philco Corporation and used Pulse Code Modulation, if I recall. The
microwave system was sold to a communications common carrier (now
Sprint) after a few years but it is still in service, I believe. Transco
(now Williams Pipeline Company) is one of many subscribers to the
service I believe.

Microwave repeaters located at about 20-mile intervals can provide
low-noise and high-reliability communications when properly designed.

In the 1950`s, I marveled as I commuted to work on a stretch of road
which ran between Lisbon and O`Porto, watching the Portuguese Post,
Telephone, and Telegraph Company laying coaxial cable alongside.

Cable is more vulnerable to damage, harder to repair, and surely costs
more than microwave. It was none of my business. I was a foreigner in
their country.

Best regards, Richard Harrison, KB5WZI

Cable doesn't fade from atmospherics.

--

73
Hank WD5JFR
"Richard Harrison" wrote in message
...
Reg, G4FGQ wrote:
"A transatlantic coaxial cable, 2000 miles long, has an overall
attenuation at 5 MHz of around 4000 decibels."

That sounds reasonable as it is only 2 dB per mile. A mile is 52.8
increments of 100 feet, so that would produce about 0.038 dB/100 feet.

The lowest loss 75-ohm cable I found listed in the ARRL Antenna Book
table is 7/8-inch Hard-line at about 0.1 dB/100 feet at 5 MHz. For an
intercontinental link, you would strive for better as Reg indicated.

One problem of cable is that it has constant loss. Every cebtimeter of
length takes the same percentage loss of the remaining energy. Hence,
dB/ 100 feet.

Not so with radio in free-space. Getting rid of the wires ends their
attenuation. Loss is then due to decreased signal in a square unit of
the wavefront caused by expansion or thinning of the signal. The
"unattenuated" signal decline is 6 dB every time distance from the
source doubles, be it one mile or 1000 miles. The signal power level at
a point is 1/4 the power it had for the same area at 1/2 the distance
from the source.

We could`not communicate by wire with our space probes due to too much
loss even were the wires a practical alternative.

To cross an ocean, cable solves the problem of repeater placement. The
signal must be regenerated before it falls into noise. The repeaters are
"simply" integrated into the cable at proper intervals. The first
transatlantic cable message was sent by Queen Victoria to the American
President.

Ashore and on distant offshore platforms, I`ve puzzled why microwave was
not used instead of cable. Privacy may be one reason, but encryption,
route switching and other techniques could make theft of information
from thin air more difficult than other theft. There are always
beneficiaries of the status quo who make change difficult to impose.

In the early 1950`s, Houston`s Transcontinental Gas Pipeline Company
(Ken Lay was an officer of "Transco" before moving to Enron) built a
private microwave system from its heasdquarters to New Jersey along its
pipeline. I recall looking the new system over. It was supplied by
Philco Corporation and used Pulse Code Modulation, if I recall. The
microwave system was sold to a communications common carrier (now
Sprint) after a few years but it is still in service, I believe. Transco
(now Williams Pipeline Company) is one of many subscribers to the
service I believe.

Microwave repeaters located at about 20-mile intervals can provide
low-noise and high-reliability communications when properly designed.

In the 1950`s, I marveled as I commuted to work on a stretch of road
which ran between Lisbon and O`Porto, watching the Portuguese Post,
Telephone, and Telegraph Company laying coaxial cable alongside.

Cable is more vulnerable to damage, harder to repair, and surely costs
more than microwave. It was none of my business. I was a foreigner in
their country.

Best regards, Richard Harrison, KB5WZI

Rich H. wrote:
"Getting rid of the wires ends their attenuation."
--and--
"Loss is then due to decreased signal in a square unit of
the wavefront caused by expansion or thinning of the signal."

I missed this on my first read of your post--I think there is some
measureable amount of attentuation by the
(a)ether (is the (a)ether a superconductor?)... it is just a component of
the "loss" noted in the second clip, above...

.... not wishing to make a bit point of it... just pointing it out...

Warmest regards,
John

"Richard Harrison" wrote in message
...
Reg, G4FGQ wrote:
"A transatlantic coaxial cable, 2000 miles long, has an overall
attenuation at 5 MHz of around 4000 decibels."

That sounds reasonable as it is only 2 dB per mile. A mile is 52.8
increments of 100 feet, so that would produce about 0.038 dB/100 feet.

The lowest loss 75-ohm cable I found listed in the ARRL Antenna Book
table is 7/8-inch Hard-line at about 0.1 dB/100 feet at 5 MHz. For an
intercontinental link, you would strive for better as Reg indicated.

One problem of cable is that it has constant loss. Every cebtimeter of
length takes the same percentage loss of the remaining energy. Hence,
dB/ 100 feet.

Not so with radio in free-space. Getting rid of the wires ends their
attenuation. Loss is then due to decreased signal in a square unit of
the wavefront caused by expansion or thinning of the signal. The
"unattenuated" signal decline is 6 dB every time distance from the
source doubles, be it one mile or 1000 miles. The signal power level at
a point is 1/4 the power it had for the same area at 1/2 the distance
from the source.

We could`not communicate by wire with our space probes due to too much
loss even were the wires a practical alternative.

To cross an ocean, cable solves the problem of repeater placement. The
signal must be regenerated before it falls into noise. The repeaters are
"simply" integrated into the cable at proper intervals. The first
transatlantic cable message was sent by Queen Victoria to the American
President.

Ashore and on distant offshore platforms, I`ve puzzled why microwave was
not used instead of cable. Privacy may be one reason, but encryption,
route switching and other techniques could make theft of information
from thin air more difficult than other theft. There are always
beneficiaries of the status quo who make change difficult to impose.

In the early 1950`s, Houston`s Transcontinental Gas Pipeline Company
(Ken Lay was an officer of "Transco" before moving to Enron) built a
private microwave system from its heasdquarters to New Jersey along its
pipeline. I recall looking the new system over. It was supplied by
Philco Corporation and used Pulse Code Modulation, if I recall. The
microwave system was sold to a communications common carrier (now
Sprint) after a few years but it is still in service, I believe. Transco
(now Williams Pipeline Company) is one of many subscribers to the
service I believe.

Microwave repeaters located at about 20-mile intervals can provide
low-noise and high-reliability communications when properly designed.

In the 1950`s, I marveled as I commuted to work on a stretch of road
which ran between Lisbon and O`Porto, watching the Portuguese Post,
Telephone, and Telegraph Company laying coaxial cable alongside.

Cable is more vulnerable to damage, harder to repair, and surely costs
more than microwave. It was none of my business. I was a foreigner in
their country.

Best regards, Richard Harrison, KB5WZI