On Thu, 1 Jun 2006 03:04:33 +0100, "Reg Edwards"
wrote:

Bob asked -
For the Wireman's ladderline # 551, where would I find the line loss
at 10 mhz in db per 100 feet (and why feet, when the other
parameters
are in meters?)?

=======================================
Bob,

If you don't know the attenuation of your transmission line you
shouldn't be using it.

A standard method of defining the vital attenuation parameter of a
transmission lines is "Decibels per 100 feet at some frequency or
other." It is probably stated in that form in bibles such as ARRL
publications.

And a reputable American manufacturer will probably state it in his
sales catalogue. Or he ought to.

Frequency is mentioned because knowing the attenuation at one
frequency allows it to be accurately calculated at any other
frequency. As is done thousands ot times in the program.

The program asks for dB per 100 feet because, out of consideration for
USA citizens, the foot is the unit of length with which they are most
familiar. And for the rest of the World there is a statement in the
program notes that "100 feet = 30 metres."

The alternative to asking for dB per 100 feet at 10 MHz is to provide
a look-up table which lists by name the attenuation of hundreds of
different types of transmission line used in the USA and the rest of
the World.

Or the program could ask for conductor diameters and conductor spacing
in the case of twin lines, inner and outer diameters for coaxial
lines, also the dimensions and electrical properties of the insulating
materials. And then calculate attenuation versus frequency.

A large number of numerical program input items would detract from a
program's usefulness. Users would soon get fed up with using it. And
the programmer would get tired of writing any more.

Attenuation and Zo are the most important parameters of a transmission
line. To keep things simple for both program users AND the programmer
it is best that both parameters be entered directly.

Try Google.

The main purpose of the program is to calculate the impedance
presented to the tuner. For accuracy, line loss must be taken into
account.
----
Reg.


Got everything plugged in -- works very nicely -- thanks... fun to
change line & feedline length and see what that does at various
frequencies.

bob
k5qwg