AT&T TD-3 Manual

BELL SYSTEM PRACTICES
AT&TCo Standard
SECTION 411-100-501
Issue 2, January 1973
TD-3 MICROWAVE RADIO
OVERALL SYSTEM
TESTS
ENVELOPE DELAY DISTORTION
CONTENTS PAGE
1. GENERAL
2. TESTS
Chart 1-Envelope Delay Distortion
Measurements Using The J68347 A
3
Visual Delay Set . . • • . . . 3
Chart 2-Envelope Delay Distortion
Measurements Using the VZM-83
Distortion Measuring Set • . . • 7
.Chart 3-Envelope Delay Distortion
Measurements Using the Hewlett-Packard
KS-20548 Microwave Link Analyzer 10
Chart 4-Envelope Delay Distortion
Measurements Using the J68347 A
Visual Delay Set (Transmit) and the
Hewlett-Packard KS-20548 Microwave
Link Analyzer (Receive)
Chart 5-Envelope Delay Distortion
Measurements Using the Hewlett-Packard
KS-20548 Microwave Link Analyzer
(Transmit) and the J68347A Visual
14
Delay Set (Receive>• • . . • • 1 7
3. MOP-UP EQUALIZATION OF DELAY SLOPE
AND PARABOLIC DISTORTION • • • . 20
4. DELAY RIPPLE REQUIREMENT . • . . 22
1. GENERAL
1.01
This section contains the procedures for
making envelope delay distortion (EDD)
measurements. Procedures are given for using
the J68347 A visual delay set, the Wandel and
Goltermann VZM-83 distortion measuring set, and
•The KS-20548 Hewlett-Packard microwave link
analyzer .• If the EDD measurement is to be made
with any other type of set, the manufacturer's
instruction manual for that set should be used for
test setup and operation information.
1.02
This section is reissued to include Charts
3, 4, and 5. This reissue does not affect
the Equipment Test List.
1.03
Cross-modulation noise can be produced
whenever the FM signal being carried on
the radio channel is transmitted through any portion
of the system having either residual envelope delay
distortion or residual amplitude distortion. Envelope
delay distortion is a measure of the departure from
perfect phase linearity across the IF or RF frequency
band. Amplitude distortion is a measure of the
departure from perfect amplitude (or gain) flatness
across the IF or RF frequency band. Both distortions
must be held within tight limits if the system
cross-modulation noise objectives are to be met.
1.04
Because of the complex nature of the FM
signal, there is no simple method of
determining the cross-modulation noise from a
complicated EDD characteristic. However, it is
possible to find from the measurement, by inspection,
several simple predominant components of the
EDD characteristic, such as slope, parabola, and
ripple. Delay slope is generally the largest contributor
to the system cross-modulation noise, and, therefore,
it is essential that the slope component of the
characteristic be minimized.
1.05
Normally, some delay slope will be present
in all radio channels before mop-up equalization
is applied. ~ome delay slope will be introduced
by the circular and rectangular waveguide runs at
a radio station. The amount of delay slope introduced
over a 12-MHz channel is directly proportional to
the lengths of the waveguide runs involved. This
source of slope arises because the velocity of
propagation of the signal through the waveguide
decreases as the frequency approaches the cut-off
frequency of the waveguide.. A small residual
delay slope in each hop also can be caused by some
of the IF circuits in the radio receiver and
transmitter, and by the channel separation network
© American Telephone and Telegraph Company, 1973
Printed in U.S.A.
Page 1