Lesson 3/Learning Event 3
(d) Display key.
The display switch (key) also works in
conjunction with the three-level impulse noise hits and dropout test. When
the switch is in the IMPULSE NOISE position, the display will show the hits
at the low, medium (MID) and high frequency spectrum of the channel under
test.
When the switch is in the HIT & DROPOUT position the display will
show phase hits, dropouts and gain hits.
(e) Envelope delay.
The envelope delay section consists of one
indicator light and three push button switches that are used to perform
return reference envelope delay test. The indicator light (NO LOOP) will be
illuminated any time the envelope delay loop is broken, or the signal is
attenuated to the point that an accurate reading cannot be made. The DELAY
NORM AND REPEAT push button switches, determine whether the test set will be
used to measure envelope delay (NORM) or retransmit (REPEAT) the delay
signal received from the distant end. The DELAY ZERO push button switch is
used in conjunction with the envelope delay measurements. When the test set
is adjusted to the desired reference frequency, pressing the DELAY ZERO
switch will establish a zero microsecond delay reference.
All delay
measurements are then relative to this reference point.
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