BIRD Thruline 4304A, Руководство по эксплуатации, Страница: 20 / 34

RF Directional Thruline® Wattmeter 4304A
10
Transmission line theory shows that if the line length changes by exactly
1

2
wavelength, the impedance at the transmitter will not change. So, to have
identical match with the Bird 4304A in or out of the circuit, it is necessary to
insert or remove
1

2
wavelength of line (including the wattmeter). Use a length
of cable which, when added to the wattmeter, equals
1

2
wavelength at the
frequency of interest. If more than one frequency is involved, a separate cable
length is required for each. See
Figure 5
for sample cable lengths.
Note:
Cable length is measured from end to end of the outer con-
ductor of the connectors, except for UHF and mini-UHF plugs where
it is measured from tip to tip of the center pins.
Note:
Dimensions shown are for solid polyethylene cable such as
RG-58C/U or RG-8/U, which have a velocity of propagation 66% of
that of air. If RG-58 or RG-8 type cables with foam polyethylene
(v.p. of 79%) are used, multiply the dimensions in the graph by the
ratio of the relative velocities; 79% ÷ 66% = 1.2 in this case.