You're correct that CB whips, 2 meter whips, AM broadcast towers, and
the like are just fine because of their large diameter.

But think about it a little bit. If you reduce the frequency by a factor
of two, the length of a resonant antenna increases by a factor of two.
The skin depth decreases by a factor of the square root of two, so the
resistance per unit length increases by this factor. So at half the
frequency, the resistance of a resonant antenna has increased by the
square root of two. Furthermore, you don't typically use 1/4 inch
diameter wire for an HF dipole, for example. (And most hams presumably
wouldn't make an HF dipole from surplus broadcast towers -- but then I
haven't seen your station.) Assuming you're using a resonant antenna of
constant diameter, the loss gets higher as the frequency gets lower.

Now go back and read what I wrote. Notice that I said that the wire was
most likely to be a problem with antennas on the order of an 80 meter
dipole length. Now you understand (I hope) why that qualification.

If you use an antenna at a frequency higher than its primary resonance
(such as a 40 meter dipole on 15, or a G5RV on a high frequency band),
the loss gets greater yet, since the skin depth decreases with frequency.

Roy Lewallen, W7EL

Richard Harrison wrote:
Roy, W7EL wrote:
"Some stainless steels are ferromagnetic, with a permability I`d guess
at 100 or more. That reduces the skin depth, and therefore increases the
RF resistance by a factor of 10."

Being ferromagnetic does not disqualify an antenna material. Most CB
whips are stainless steel. They aren`t too lossy because they are only
about 1/4-wave at 27 MHz and must be large enough in diameter to be
durable. In the range of 0.55 MHz to 1.7 MHz, most transmission is from
ordinary non-stainless steel towers. The only coating on many of these
is paint. The cross-section to length ratio is economically small, but I
doubt the loss added by using nonplated steel could be measured.

Best regards, Richard Harrison, KB5WZI

Roy, W7EL wrote:
"Notice that I said that the wire was most likely to be a problem with
antennas on the order of an 80 meter dipole length."

80 meters isn`t the lowest nor the highest frequency ham band, but could
be a problem for various reasons. Loss is directly proportional to
resistance in the familiar current squared times resistance formula.

Resistance increases due to skin effect only as the square root of the
frequency while resistance varies directly with the conductor length
which varies inversely with frequency.

Loss gets worse for a given wire size as frequency drops because you
need longer wire for a 1/4 wavelength. It doesn`t get worse as fast as
it would if there were no skin effect because as frequency lowers,
current penetration grows and wire resistance drops due to reduction of
the skin effect. But, the longer wire is inevitable along with its
higher resistance at the lower frequency.

At RFE, as soon as a new frequency became available we would often erect
a Signal Corps rhombic kit and start broadcasting. These weren`t made
for 100KW so the dissipation lines soon melted and the rhombics became
bidirectional.

At the end of WW-2, many Central Europeans fled to South America. When
we strengthened and replaced our dissipation lines, we discovered we had
built a large loyal audience among the fugitives. Not too surprising
since we were programming with some of their favorite entertainers who
were also exiles. Too bad we had to eliminate the signal flooding South
America, but other broadcasters had claims on the frequencies we were
using for a South American audience.

Best regards, Richard Harrison, KB5WZI

On Mon, 30 Aug 2004 10:36:57 -0500, (Richard Harrison)
wrote:

Roy, W7EL wrote:
"Notice that I said that the wire was most likely to be a problem with
antennas on the order of an 80 meter dipole length."

80 meters isn`t the lowest nor the highest frequency ham band, but could
be a problem for various reasons. Loss is directly proportional to
resistance in the familiar current squared times resistance formula.

Resistance increases due to skin effect only as the square root of the
frequency while resistance varies directly with the conductor length
which varies inversely with frequency.

Loss gets worse for a given wire size as frequency drops because you
need longer wire for a 1/4 wavelength. It doesn`t get worse as fast as
it would if there were no skin effect because as frequency lowers,
current penetration grows and wire resistance drops due to reduction of
the skin effect. But, the longer wire is inevitable along with its
higher resistance at the lower frequency.

At RFE, as soon as a new frequency became available we would often erect
a Signal Corps rhombic kit and start broadcasting. These weren`t made
for 100KW so the dissipation lines soon melted and the rhombics became
bidirectional.

At the end of WW-2, many Central Europeans fled to South America. When
we strengthened and replaced our dissipation lines, we discovered we had
built a large loyal audience among the fugitives. Not too surprising
since we were programming with some of their favorite entertainers who
were also exiles. Too bad we had to eliminate the signal flooding South
America, but other broadcasters had claims on the frequencies we were
using for a South American audience.

Best regards, Richard Harrison, KB5WZI

Very interesting, Richard. Were the rhombic dissipation lines made of high
resistance wire? And where were the transmitters located that flooded SA? And
what SA countries did the fugitives concentrate in?

Walt

There's been much discussion.

The end-to-end RF loss resistance of a half-wave copper dipole is given by -

R = Squareroot( Lambda / 2 ) / D ohms.

Where Lambda is the free-space wavelength in meters and D is wire or rod
diameter in millimetres. Much more simple and easier than measuring it.

For example, the overall loss resistance of a 14 awg, 40m dipole, is 2.73
ohms.

For another metal, multiply R by the square root of resistivity and the
square root of permeability, both relative to copper.
----
Reg, GFGQ

Walter, W2DU wrote:
"Were the rhombic dissipation lines made of high resistance wire?"

The Signal Corps rhombic kits we had were manufactured by the Wind
Turbine Company and were most distinguished by a unique one-piece
ceramic insulator designed to hold both transmission line cables as it
sat atop a support. The lines were made of 3 no. 12 Copperweld wires
twisted together. We discarded these as our transmission lines needed
larger cable and wider spacing for the same 600-ohm line.

The kit included short tower sections meant as transmission line
supports. Triangular tower sections were made of (3) vertical steel rods
with wire sides where the wire weaved back and forth between rods. Every
steel piece was welded at intersections and assemblies were all
hot-dipped galvanized. They were good structures.

The rhombic curtain was a 3-cable type, spread apart vertically at the
side towers to reduce impedance variations. The same Copperweld cable,
(3) twisted no. 12`s, was used for each of the 3 separate cables, as
that used in the transmission line.

An exponentially tapered feedline was used to attach the wide-spaced
attachment to the curtain overhead to the more narrow transmission line
down below. Its aim was matching 800 ohms to 600 ohms.

My recollection is that the dissipation line at the far end of the
rhombic terminus was itself made to match 800 ohms rather than using
another tapered line. Too many insulators of varied size, I suppose. So,
the down line at the far end had uniform spacing. The dissipation line
itself was relatively small stainless steel wires until we replaced them
with much larger wire and spacings. It ran back and forth down the
centerline of the rhombic.

The rhombics were aimed at central Europe from Portugal. Their reverse
radiation bathed nearly all of South America with strong signals for as
long as the rhombics were without dissipation lines.

I have no statistics on where the fugitives concentrated. I know that
before WW-2, many Europeans had sought opportunity in South America. The
war made it plain that the persecuted needed a new haven outside of
Europe. It was also clear that the persecutors might escape
responsibility if they fled Europe following the war.

I`ve personally been struck by the numbers of people I`ve encountered in
Santiago de Chile, Buenos Aires, and Rio de Janeiro, obviously
residents, not tourists, speaking Central European languages. A lot of
these newer arrivals already had families residing in those countries.

There are a lot of Brits in South America too. In Argentina, many came
to do good and stayed to do well. Hurlingjham is a British neighborhood
in B.A. with its own polo grounds. People send their fourth generation
offspring back "home to the U.K." for education. The main street (high
road) of Santiago is Avenida O`Higgins.

Best regards, Richard Harrison, KB5WZI

O'Higgins is not English. He was an important part of the fight to
breakaway from Spain.

I found the descriptions of the rhombics interesting. Thanks.

My son changed my operating system over the weekend. The change was
long overdue. This is first test of whether I am able to post.

73 Mac N8TT

--
J. Mc Laughlin; Michigan U.S.A.
Home:
"Richard Harrison" wrote
snip
There are a lot of Brits in South America too. In Argentina, many came
to do good and stayed to do well. Hurlingjham is a British neighborhood
in B.A. with its own polo grounds. People send their fourth generation
offspring back "home to the U.K." for education. The main street (high
road) of Santiago is Avenida O`Higgins.

Best regards, Richard Harrison, KB5WZI

On Mon, 30 Aug 2004 21:12:06 -0400, wrote:

O'Higgins is not English. He was an important part of the fight to
breakaway from Spain.

"Richard Harrison" wrote
snip
Hurlingjham is a British neighborhood
in B.A. with its own polo grounds. People send their fourth generation
offspring back "home to the U.K." for education. The main street (high
road) of Santiago is Avenida O`Higgins.

Hi All,

Buenos Aires certainly does not lack for Spanish names in its various
barrios and along its streets, but not all of them are mono-cultural.
Notable in both their in-country airport and a road nearby is the name
Jorge Newberry. The Thames can be found in Palermo. You can stay the
night in the Hotel Waldorf or Hotel Lancaster in the Retiro and shop
at Kelly's - the Irish Embassy is also located in this barrio. There
is also the British Arts Center in the Retiro, as well as the Torre de
los Ingleses (a monument to the English) across the street from the
Plaza Libertador General San Martin (which contains a wall of names of
the fallen in the Malvinas).

When I visited the Cementario de la Recoleta there were plenty of
English and Irish surnames from 150 years ago - not unusual at all.
However, Buenos Aires also sports a very large population of Italians
and is the home to the largest settlement of Jews outside of Europe
and the US. When we were in La Plata, we ate at schnitzel at a
Bavarian styled restaurant.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
"You can stay the night in the Hotel Waldorf or the Hotel Lancaster in
the Retiro and shop at Kelly`s-"

I usually stayed at the Claridge just off the pedestrian shopping street
La Calle Florida. The company installed me there on my first arrival in
Buenos Aires as I had no preference. When I returned there after a 6
month absence and was joyfully greeted by my name from the doorman. I
was hooked.

On one of my 6 month tours in Argentina, I decided to give the Sussex
Hotel across the street from the Claridge a try as all the oil field
hands seemed to stay there. I arrived out of cigarettes, dying for a
smoke, and asked the desk clerk if the Sussex had a smoke shop. When the
clerk said no, I told him to send my luggage on up to my room while I
shopped for cigarettes.

The clerk spyed me when I re-entered the hotel and called me over to
give me a message from my wife who was very eager to see me. I thanked
him although at that time I`d never been married, but I had discovered
the main attraction of the Sussex Hotel! And they say a gringo is no
damn good when he speaks Spanish!

Best regards, Richard Harrison, KB5WZI