Bird Technologies 4304A - Manual (Page 19)

8
Component Testing
The Bird 4304A is very helpful in component testing, and may be employed in
several ways:
Note: Measuring small attenuations requires correction for normal
instrument errors. For two wattmeters, do this by simply connecting
the wattmeters directly, with no line between them, and adjusting
their zero settings. For one, make sure to note exact readings, or their
difference, on the initial equality check, and correct for this.
•
Insertion VSWR or
φ may be measured by placing the component
between the wattmeter and a good load resistor.
•
Attenuation (power lost by heat in a line) as well as insertion VSWR or
φ
may be measured by inserting the unknown line between two Thruline
wattmeters, or between a Thruline wattmeter and a Termaline absorp-
tion wattmeter.
•
Line loss using open circuit calibration: The high directivity of elements
can be exploited in line loss measurements by having the load connec-
tor open or short circuited. The forward and reflected waves then have
equal power, so that
φ = 100% and ρ = ∞. Open circuit testing is pre-
ferred, because a high quality open is easier to create than a high qual-
ity short. To measure insertion loss, use an open standard to check
forward and reverse power equality, then connect an open, unknown
line to the wattmeter. The measured
φ is the attenuation for two passes
along the line (down and back). This can then be compared with pub-
lished data for line type and length (remember to halve N
db
or double the
line length).
Note: This measurement should be supplemented with either time
domain reflectometry or dc continuity and leakage checks, since the
attenuation measurement alone cannot detect faults such as open or
short circuits partway down the line.