Reg Edwards wrote:
The complete equation is -

Attenuation = R/2/Ro + G*Ro/2 Nepers

where G is the conductance of the dielectric, which is small for
materials such as polyethylene and Teflon. And 1 Neper = 20/Ln(10) =
8.686 dB.

Reg, I didn't disagree with your equation. I disagreed with this
statement of yours:

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

That is simply not a true statement. #13 RG-213 wire is actually
***LARGER*** than #18 ladder-line wire yet the coax still has the
higher matched-line loss. If your statement were true, #13 RG-213
would have lower losses than #18 ladder-line but it doesn't.

The number one reason that coax has higher matched line losses
than ladder-line is NOT primarily due to wire size. It is primarily
due to the differences in characteristic impedance, as I said earlier,
and as proved by your equation above.
--
73, Cecil http://www.qsl.net/w5dxp


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Reg Edwards wrote:
All the so-called SWR meter tells you is whether or not the
transmitter is being loaded with 50 ohms.

This may be a useful thing to know. But it is NOT SWR. Where is the
line on which the SWR is supposed to be measured?

If the reflected power on the line between the transmitter and
the meter equals zero:

SWR = [SQRT(Pf)+SQRT(Pr)]/[SQRT(Pf)-SQRT(Pr)]

SWR = [SQRT(Pf)+0]/[SQRT(Pf)-0] = 1:1
--
73, Cecil http://www.qsl.net/w5dxp


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Reg:

You kinda relate SWR meters to "time", huh? Well, I am used to being fooled
by "non-existant" "things"-"values" which we plug into formulas and somehow
get workable results back!!!! The "Unified Antenna Theory" will be a nice
thing--when it finally gets here... so, a SWR meter which doesn't work as
"mentally modeled"--hey, perfectly understandable!!!

So, not in anyway in disagreement with you, just poking a bit of fun at the
way things work...

Like I say, I miss the old PA tubes--dull almost dark red glow from the
plates--good to excellent... brighter almost cherry red--danger will
robinson!!!!... orange'ish-red--time to buy new finals!!!!! grin

I am at a complete loss on the email... may have picked up some malicious
email from a "fan" of mine... have worn myself out attempting to find the
problem--you can count on me NOT giving up until it is fixed... I keep a
seperate computer for use here--this demonstrates why...

Warmest regards,
John
--
If "God"--expecting an angel... if evolution--expecting an alien... just
wondering if I will be able to tell the difference!

"Reg Edwards" wrote in message
...
| John,
|
| All the so-called SWR meter tells you is whether or not the
| transmitter is being loaded with 50 ohms.
|
| This may be a useful thing to know. But it is NOT SWR. Where is the
| line on which the SWR is supposed to be measured?
|
| By the way, I think I am receiving all your emails. But you do not
| appear to be receiving any of mine. Don't think I do not wish to
| speak to you.
|
| Could you check that you can receive other people's emails?
| ----
| Reg, G4FGQ
|
|

Cecil Moore wrote:
Reg Edwards wrote:

The complete equation is -

Attenuation = R/2/Ro + G*Ro/2 Nepers

where G is the conductance of the dielectric, which is small for
materials such as polyethylene and Teflon. And 1 Neper = 20/Ln(10) =
8.686 dB.


Reg, I didn't disagree with your equation. I disagreed with this
statement of yours:

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

As an illustrated example: Assume a parallel feedline made from #24
wire and having a characteristic impedance of 600 ohms.

What size would the wire in 50 ohm coax have to be to equal the HF
matched line loss of the #24 600 ohm line? (The wire in the coax has
to be 12 times as conductive as the wire in the parallel feedline in
order to offset the effect of Z0.)

A rough estimate indicates that the #24 600 ohm line has approximately
the same matched line loss as RG-213 with its #13 wire.
--
73, Cecil http://www.qsl.net/w5dxp


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Cecil Moore wrote:
Reg Edwards wrote:

You will get all sorts of technical reasons for lower loss. But
essentially -

The wires in high impedance balanced pair lines are thicker than
the
inner conductor of coaxial lines.

Thicker wires mean lower resistance.

Lower resistance means lower loss.

That is true. But the number one reason that matched line loss
for 450 ohm ladder-line is lower than matched line loss for RG-213
at HF is the effect of (characteristic impedance =3D load) which is
the same effect as Ohm's law.

Given RG-213 vs 450 ohm ladder-line the losses are *roughly*
equal when:

SWR(coax)/50 =3D SWR(ladder-line)/450

or, in general, when:

SWR1/Z01 =3D SWR2/Z02

Wunnerful. But out here in the realities of practical (God forbid)
applications of the various types of backyard feedlines there's a
persistent rumor going back decades to the effect that decent open-wire
feedlines have significantly lower dielectric losses than "ham-level"
coax under all VSWR condx. So there are conductor *and* dielectric I=B2R
losses to consider in this discussion yes?

--
73, Cecil http://www.qsl.net/w5dxp

w3rv


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Brian Kelly wrote:
So there are conductor *and* dielectric I²R
losses to consider in this discussion yes?

Dielectric losses are usually considered to be
negligible at HF.
--
73, Cecil http://www.qsl.net/w5dxp

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Reg:

I am not after your scalp, trust me...

However, as I ready for bed, I was thinking--on the age of my coax...
although some may be as new as 3 years old... most is greater than 5, and I
bet the run to my 1/2 vertical is 20 years or better....

Sometime in the past, I remember reviewing data on loss in coax going up
with age.... not that it would amount to an important loss... but still, it
must be a measurable amount...

Oh, and strange how this all keeps touching on the matter I am constantly
holding at hand... but that "skin effect"... seems like copper becomes an
"impedance" at high freqs.... those little electrons in the wire just can't
keep pumping the charge fast enough... seems like that old rf there is
considering the ether itself (dielectric in coax) as a better choice of
travel than the copper atoms...

Warmest regards,
John
--
If "God"--expecting an angel... if evolution--expecting an alien... just
wondering if I will be able to tell the difference!

"Reg Edwards" wrote in message
...
| The number one reason for attenuation being higher is because the
| conductor diameter is smaller and, as a consequence, its resistance
| is
| higher.
|
| The exact simple mathematical relationship is -
|
| Line attenuation = 8.69*R/2/Ro dB.
|
| Where R is the resistance of the wire and Ro is the real component
| of
| line impedance, all in ohms.
|
| Make a note of it in your notebooks.
|
| And, hopefully, that should be the end of the matter. But, knowing
| you lot, it probably won't be. ;o)
| ----
| Reg, G4FGQ
|
| ================================
|
| To you all.
|
| As predicted, I appear to have stirred up a hornet's nest.
|
| First of all, give credit to where credit is due. The simple equation
| is not due to me but to Oliver Heaviside, 1850 - 1925. May God rest
| his soul. And mine!
|
| It applies from DC to VHF where the predominent loss is due to
| conductor resistance including skin effect. At higher frequencies, say
| above 0.5 GHz, loss in the dielectric material begins to play an
| important part.
|
| The complete equation is -
|
| Attenuation = R/2/Ro + G*Ro/2 Nepers
|
| where G is the conductance of the dielectric, which is small for
| materials such as polyethylene and Teflon. And 1 Neper = 20/Ln(10) =
| 8.686 dB.
|
| The Neper is the fundamental unit of transmission loss per unit length
| of line, familiar to transmission line engineers. It is named after
| Napier, a canny Scotsman who had something to do with the invention of
| Logarithms around the 18th Century.
|
| Attenuation is simply the basic matched loss of a particular line,
| unaffected by SWR and all the other encumbrances which amateurs such
| as W5DXP ;o) worry about. KISS.
|
| Incidentally, the additional-loss versus SWR curves, published in the
| ARRL books and copied by the RSGB, for many years, are based on an
| incorrect mathematical analysis. But they are near enough for
| practical purposes.
|
| Not that SWR matters very much. SWR meters don't measure SWR on any
| line anyway. You are all being fooled. ;o) ;o) ;o)
| ----
| Reg, G4FGQ
|
|

I have never heard of ageing effects in copper or polyethylene - or
ancient ebonite spacers even.

The very first coaxial carrier communications cable was laid in Great
Britain by the Post Office, around 1937, between the cities of
Manchester and Leeds. There were 4 coaxial tubes inside a lead
sheath. Outer conductors = 0.375". Inner conductors = 0.1", which
later became the standard. Mostly air spaced. Inner conductors were
supported by ebonite disks or similar material, spaced at about 1.5".
Polyethylene was still waiting to be invented. Working frequencies
from 60 kHz to about 2 MHz. Repeater spacing about 5 miles.

Around 1960 I had the opportunity to test sections of this cable. As
far as I could judge it was in perfect working order. Bear in mind it
is possible to detect small changes in attenuation only by looping
back on very long lengths. It cannot be done in the lab.

I imagine coax, with temperature expansion and contraction, very
slowly 'breathes' through the ends and draws in humid atmospheric
pollution. Perhaps after 50 years it may have some minute detectable
effect on attenuation and appearance. Attenuation is the last
parameter to fail. Far more serious things have to happen to a
transmission line before loss becomes noticeable.

For example, a coax line can be almost flattened with a hammer over a
length of several feet which will make a shocking mess of impedance.
Yet, provided the inner and outer conductors are not in contact with
each other, additional loss will be undetectable.

=========================

Nothing happens to metallic copper with frequency. But copper
conductors also have internal inductance in addition to conductance.
Inductive reactance increases with frequency. The increase in
inductive reactance begins at the centre of the conductor and drives
the current outwards towards the surface or perimeter. At
sufficiently high frequencies the current is forced to flow only on
the conductor's skin.

The conductance of copper remains the same. But the cross-section of
the conductor allowed to the current is very much reduced and so the
effective resistance per unit length increases together with the
inductive reactance.

It's an interesting fact that at frequencies where skin effect is
fully operative, conductor inductive reactance and resistance become
equal to each other. Measure one and you also know the other.
----
Reg, G4FGQ

I should have mentioned, the Manchester-Leeds Number 1 Coaxial Cable
had an impedance of 75 ohms. The impedance at which, for a given
price of copper, in those far-off days, had the lowest attenuation per
mile. 75 ohms has stuck as the Standard..

The distance between Manchester (then the centre of the cotton
industry) and Leeds (then the centre of the woolen industry), by road,
over the beautiful Lancashire and Yorkshire moors, is about 40 English
miles. By correct choice of impedance the conscientious engineers of
that age could have saved as much as £5,000 per mile in the price of
copper, to be formed in the manufactories into copper tapes for outer
coaxial conductors, and drawing copper wire from 3-ton billet-form
down to exact precision-size wire through water-cooled diamond dies.
It was and still is a precision manufacturing industry.

More savings occur in the distance between repeater stations. If
attenuation performance requirements can be met with one fewer
repeater station, the cost of a whole building, power supplies and
transmission equipment can be saved.

Although communications have shifted to digital, cables still matter.
But eventually optical fibers will take over the long distance
communications.

Radio Amateurs, with a little money to burn, never become involved
with such mundane matters. They are more interested in what they
imagine the SWR meter tells them. But if that keeps them happy then
so be it. I am an amateur myself. I have a call sign which sounds
very nice in morse code. Why should I disillusion them?
----
Reg, G4FGQ

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

So there are conductor *and* dielectric I²R
losses to consider in this discussion yes?


No.