TM 11-6625-1559-12
line system may be measured by the sweep gen-
end of the cable is short-circuited.
erator and a delay line, which can be made up
from coaxial cable, the type and dimensions de-
e. Terminate the far end of the delay line
pending upon the frequency range and the par-
titular type of impedance to be tested. Make
proper fittings to avoid any additional mismatch
this measurement as follows:
problems.
f. If the impedance termination is resistive or
broadband and matches the impedance of the de-
jack to one of the DETECTOR input jacks; use
lay line, the loops will straighten out into a
a short length of test cable with UG-88/U con-
nectors.
b. Connect the other DETECTOR jack to a
matching characteristic, only a few of the loops
delay line made up of low-loss 50-ohm coaxial
will be straightened out, corresponding to the
cable. The length of this cable should be long
frequencies at which the delay line is matched,
enough to include approximately 8 to 10 half-
waves of the frequency being measured.
Note. A
half-wavelength of cable
may be
calculated
by using either of the following formulas:
Frequencies
(1) For solid polyethylene cables:
If other than the built-in 60-cycle sweep fre-
quency is required for special tests, an external
333
drive voltage may be connected at the rear of
Length in feet =
.
the power supply chassis, as follows:
Frequency in MHz
a. Disconnect the jumper from terminals 2 and
3 on the EXT WOBB DRIVE terminal strip.
(2) For aid dielectric cables:
b. Connect an external sweep voltage, from dc
492
to 60 cycles, not to exceed 3 volts, between ter-
Length in feet =
.
minals 1 and 2 of the terminal strip.
Frequency in MHz
c. The maximum and minimum sweep widths
obtainable from this external voltage may still
through l, to obtain the best display on the os-
be controlled with the SWEEP WIDTH switch
cilloscope screen.
and SWEEP WIDTH control on the sweep gen-
erator.
loops represent standing waves reflected back
from the open end of the cable, the number of
a. Set the POWER switch to OFF position.
loops depending upon the frequency and length
of cable. A pattern that resembles that shown
and MARKER GAIN switches to in position.