Bird Technologies 4314C - Manual (Page 27)

15
Determining Attenuation with a Single Wattmeter
Note: This measurement must be supplemented with a reflected
power to forward power ratio check while using a load or with a DC
continuity check or leakage check, since open circuits or shorts may
exist part of the way along the line. The ratio determined in these tests
should be viewed as a rough estimate, since 100% of the power at the
open connector will not be reflected back.
Open Circuit Method
1. Attach an RF generator to the wattmeter’s input port.
2. Attach the section of transmission line that is to be measured to the output
port.
Note: The line section should be left open-ended.
3. Apply power.
4. Measure the Forward Power (P
fwd
).
5. Measure the Reflected Power.
6. Divide the Reflected Power reading in half to determine the Reflected
Power in the transmission line (P
rfl
).
Note: Because the power drop is being measured twice (down and
back).
7. Convert the reading to decibels by using this equation:
Short Circuit Method
Perform the Open Circuit Method with the exception of using a Short standard
on the end of the line being measured.
Note: The open circuit method is preferred because the ratio
(reflected power to forward power) is easier to achieve in an open cir-
cuit.
dB 10
P
rfl
P
fwd
----------- log =