On Sat, 11 Aug 2007 21:44:08 -0400, Walter Maxwell wrote:
I haven't read all the posts in this thread, so I'm not sure that the method I'm advancing for measuring line
loss has not already been discussed.
The method I'm suggesting measures the input impedance (R and jX) of the line in question with the opposite
end of the line terminated first with an open circuit and then with a short, at a frequency where the line
will be close to lambda/8. With low-loss lines the R component will be very small, requiring an RF impedance
bridge that can produce accurate values of R in the 0.2 to 2-ohm range. (The General Radio GR-1606A is a
typical example, which, while using this procedure, will yield answers of greater accuracy than the methods
described in the current posts.) With the 1/8wl line the + and - reactances appearing in the measurements will
be approximately the value of the line Zo.
The open and short circuit values are then plugged into a BASIC program that I wrote years ago, which appears
in Chapter 15 of both Reflections 1 and 2. It also appears on my web page at www.w2du.com. The program outputs
the line attenuation, the complex Zo, and the electrical length of the line. The program solves the equations
appearing in Chipman's "Theory and Problems of Transmission Lines," Page 135.
On my web page go to 'View Chapters of Reflections 2' and click on Chapter 15 to see the detailed explanation
of the procedure.
The BASIC program TRANSCON (Transmission-line Constants) is listed there, but to save your having to load the
program from the typed list I will email a copy of the actual operable program to anyone who requests it,
addressing your request to .
I hope this suggestion will prove to be of value.
Walt, W2DU
Some additional information that can make it easier to follow the procedure. The section of Chapter 15
describing the line attenuation measurement procedure is Sec 15.3.1, Calibration of the Feedline, Page 15-3,
Chapter 15, and the table showing the results using the TRANSCON program is Fig 15-1, Page 15-4 The TRANSCON
program listing is on Page 15-22.
Walt, W2DU