Peter,

Soon after WW2 the Cable & Wireless company was 'nationalised' and became a
part of the British General Post Office. The GPO, in effect, was a giant
government department with 250,000 employees world wide. At its head was the
Postmaster General, a politician, a minister of government next in authority
to the prime minister (Clement Attley who had usurped Churchill). All other
employees, including the usually distinguished Engineer-in-Chief, down to
postmen, telegram boys on motor bikes and pretty female telephone operators
were civil servants.


C&W was the GPO's overseas arm distributed around the far-flung Empire on
which the sun never set. As the whole of my 40 years telecoms career was
with the GPO (later British Telecom and The Royal Mail to be asset-stripped
by Mrs Thatcher) you might say that for a period I was a C&W employee. At
any rate we were all contributing to the same pension scheme.


One of the Engineer-in-Chief's domains was his Research Department based at
Dollis Hill, N.London. It was the British renowned equivalent of Bell labs.
Formally I was a member of the E-in-Chief's Cable Test Section, a
non-descript name which covered a multitude of sins. I once met Josephson of
Junction fame with some of his equipment in a broom cupboard under the
stairs at DH. But at that time research was being concentrated on submerged
deep-sea repeaters, reliablity of thermionic tubes, and on a new,
light-weight oceanic cable with its strength member being the coaxial inner
conductor itself. It consisted of a bundle of high-tensile steel wires
covered with a seamed copper tape. I designed the mobile transmission test
equipment used at the cable factory in Southampton docks. To determine
temperature coefficients of line loss and other properties the last decade
of the home-brewed comparison attenuator was in steps of 0.001 decibels. I
also recall the all-tube equipment incorporated what must have been one of
the first of the phase-locked loops. RF signal switching circuits used
high-speed, mercury-wetted relays. To get everything to work properly in
the lab all at the same time I had to haggle my boss (who hadn't any idea
what it was all about) to specially import a Tektronics double-beam scope
from the States.


It will be appreciated cable loss across the Atlantic can amount to 4000
decibels. A prediction error of 0.5 percent involving temperature
coefficients can cause HF signal levels to disappear in thermal agitation
noise or LF signals to overload the last repeater into a state of
intermodulation paralysis. Aaah! - the romance of it all.


Never met up with the famous "Cyrus Field" cable layer. But I've had spells
at sea on HMTS (Her Majesty's Telegraph Ship) "Monarch" and "Iris" and even
privately shared most of a bottle of Scotch with Captain Evans of "HMTS
Arial" in his cabin while proceding in darkness up the English Channel back
to the ship's home port, Dover, just in time for Xmas.


There were once so many thousands of miles of disused Teed-pairs,
bridged-taps, coax, buried in GPO telephone exchanges (offices) and trunk
switching centres a national drive was organised to recover them for the
value of the metal involved. It was called "Copper Mining".


I lived for 4 years in the other Halifax, in the hills and deep valleys of
the West Riding of Yorkshire, but didn't spend much time at home to be amid
the smoking chimney stacks attached to the many woolen mills. They've now
all gone. We have other things in common besides transmission lines.


To have confidence in an analysis of an antenna as a transmission line it is
first necessary to pray and believe in the existance of single-wire
transmission lines. But Heaviside asked "Shall I refuse to eat my dinner
because I do not fully understand the processes of digestion."
----
Yours, Reg.

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


[snip]
Vary line length until it is exactly 1/4 wavelengths.

The input impedance of the 1/4-wave length of open-circuited line is
also
calculated and displayed.

It will be found that at exact resonance (vary length or frequency very
finely) the input impedance of the line will be a pure resistance ( jXin
=
0) equal to half of the of the line end-to-end wire resistance.
[snip]

This is *exactly* what my [and other's as well] line analysis computer
programs do for the analysis of so-called "bridged taps".

"Bridged taps", which are sections of open circuited transmission line
bridged across an operational transmission line, are quite common
in telephony practice. They are often placed deliberately to allow
for extra extension/party lines, or are inadvertently left in place once
a line is taken out of service. There are often several bridged taps
on a given line. These bridged taps don't affect telephony [audio] but
wreak havoc at higher frequencies for broadband signals. For
frequencies where the bridged taps represent a 1/4 wavelength, they
act as traps or notches and "suck out" the desired energy on the main
line. As such bridged taps can ruin the performance of digital subscriber
loops aka "DSL" such as ADSL/VDSL, etc. because they punch holes
in the transmission band. Several companies, and consultants
such as myself, have transmission line programs to evaluate broadband
transmission over lines with cascades of multiple guages/dielectrics and
several bridged taps. In fact several such "standard" line makeups
for evaluating the performance of DSL systems are published
in the Standards literature [ANSI T1E1.4]. My Fortran computer codes
must perforce analyze such 1/4 wave, or any wavelength for that
matter, stubs quite accurately to predict multi-megabit transmission
performance over several thousand feet of such impaired lines. :-)

But until your posting I had never thought to use them to analyze
the driving point impedances of antennas. Neat application!

[snip]
If your own programs significantly disagree then consign them to the
junk
box.
[snip]

Can't do that now, since literally millions of DSL modems are now running
around the world over lines that have been accurately analyzed using those
programs, hence they must be "right". I still use the programs in my
consulting
practice for client companies designing DSL modems who use my services.

I have never used these programs to simulate antennas yet, gotta do that
just for fun... I can set any arbitrary distribution of radiation
resistance
along the line in series with the primary parameter R(f) [of R(f), L(f),
C(f)
and G(f)] and so uniform distribution should be easy.

[snip]
. There are no references
except my tattered note books. I came across various useful
relationship
around 1960 when researching into methods of locating faults on oceanic
phone cables.
[snip]

Well you certainly predate me, I only started developing my transmission
line
analysis programs around 1971 or so and have kept *improving* them over
the
years, mostly to make contributions to my employers, clients and various
transmission standards committees [ANSI, ITU, ETSI, IEEE].

[snip]
But I daresay Heaviside preceded me. I dug up much information
and designed fault locating and other test equipment but very little was
published beyond contract manufacturing information. There were two
articles
in the house engineering journal. I worked alone with a small group of
assistants, a lab and a workshop. I did present a series of lectures
afterwards, twice in Europe. But it was all just in a day's work with
occasional trips aboard cable laying ships and at manufacturers. The
nearest
I got to the States was Newfoundland and Nova Scotia. I then shifted in
succession to several entirely different fields of operations. But no
experience is ever lost.
[snip]

Same here, as you know... I am a "fan" of Oliver's myself... and most of
my work in this area was done "in house" for various clients and never
published. Many times I felt that such work was "all done" and I was
ready
to retire it all only to have it called back into service with each round
of
higher
bandwidth systems... for various reasons detailed cable/transmission line
analysis seems to come back into favor every decade or so... these days it
is a sadly neglected subject in "skul" curricula and are few "young turks"
who can handle such problems, and so we "old farts" can't retire just yet.
:-)

Newfie and Nova Scotia, eh? Wonderful place in the summer. My wife
and I have a condominium overlooking Halifax harbour and we spend
part of the summers there. My Mom was/is a Newfie and I was
born in Halifax, Nova Scotia myself, although we are both now all
fully certified "Americans".

Did you work for Cable and Wireless at one time?

I suppose you might even have sailed on the "Cyrus Field", no?

Long live the "Telegraphist's Equations"!

--
Peter K1PO
Indialantic By-the-Sea, FL.