CDM-750 Advanced High-Speed Trunking Modem
Revision 2
Front Panel Operation
MN-CDM750
5–31
5.2.2.5.3 (CONFIG) ACM Config: Target-Es/No-Margin
The
ACM
system
is
designed
to
switch
based
on
thresholds
that
correspond
to
a
QEF
≈
10
‐
7
PER
for
each
ModCod.
Target Es/No Margin = 1.0 dB (0.0 – 4.5)
(
v
)
Use
the
ST
arrow
keys
to
select
a
margin
value
between
0.0
and
4.5
dB,
in
0.1
dB
increments.
Press
ENTER
when
done.
The
Target
Es/No
Margin
value,
used
as
a
tool
to
compensate
for
Rain
Fade,
is
added
to
the
QEF
specification
for
all
ModCods.
The
QEF
specification
for
a
ModCod
plus
the
Target
Es/No
Margin
plus
the
Modulation
Degradation
for
a
modulation
type
will
set
the
“Shift
Down”
Es/No
point
in
ACM
operation.
For
example:
The
far
end
side
of
a
link
has
a
maximum
rain
fade
slope
of
1
dB
per
second.
ACM
messages
are
sent
roughly
every
250
ms
and
it
will
take
290
ms
for
the
message
to
reach
the
near
side
modulator.
Assuming
worst
‐
case
scenario
of
a
strong
rain
fade
that
begins
just
after
sending
an
ACM
message:
•
There
could
be
250
ms
of
delay
before
the
next
message;
•
The
message
will
take
290
ms
to
traverse
across
the
satellite
link;
•
There
will
be
some
minimal
processing
time
of
20
ms
to
act
on
the
new
message
and
change
to
the
new
ModCod;
•
The
new
ModCod
signal
will
land
at
the
far
end
site
in
another
290
ms.
This
equates
to
250+290+20+290=550 ms
.
If
there
is
a
maximum
rain
fade
of
1dB
per
second,
there
could
be
as
much
as
.55
dB
of
fade
before
the
new
ModCod
is
received
at
the
fading
site’s
demodulator.
To
ensure
that
missing
a
single
ACM
message
does
not
drop
the
link,
the
user
may
want
to
add
another
250
ms,
so
now
the
max
fade
could
be
800
ms
–
or
0.8
dB
–
of
fade.
For
this
reason,
it
is
preferred
that
the
Target
Es/No
margin
be
at
least
0.8
dB.
Factory
default
is
set
to
1dB
.
5.2.2.5.4 (CONFIG) ACM Config: Degradation
Degradation: QPSK=0.0 8PSK=0.0
16QAM=1.0 32APSK=2.0
v
An
additional
level
of
signal
margin
can
be
added
to
the
QEF
switch
points
in
ACM
operation
by
adding
a
degradation
figure
per
modulation
type.
This
degradation
figure
further
increases
the
Es/No
required
to
switch
to
a
ModCod
having
a
degradation
figure
above
0.0.
Summary of Contents for CDM-750
Page 76: ...CDM 750 Advanced High Speed Trunking Modem Revision 2 Updating Firmware MN CDM750 4 12 Notes...
Page 224: ...CDM 750 Advanced High Speed Trunking Modem Revision 2 Appendix A MN CDM750 A 4 Notes...
Page 234: ...CDM 750 Advanced High Speed Trunking Modem Revision 2 Appendix B MN CDM750 B 10 Notes...
Page 256: ...CDM 750 Advanced High Speed Trunking Modem Revision 2 Appendix C MN CDM750 C 22 Notes...
Page 280: ...CDM 750 Advanced High Speed Trunking Modem Revision 2 Appendix D MN CDM750 D 24 Notes...
Page 300: ...2114 WEST 7TH STREET TEMPE ARIZONA 85281 USA 480 333 2200 PHONE 480 333 2161 FAX...
