sse
RECEIVER
Injea
1.8MHzRF_
1...
Mt4<
-,~
RF
VoIugr
CMriw
Injoo(:l:
IF
F.--cy
Measure
lrequmcy
Typial
r.
RF
VoIu!l"
1
7.8
MHz
It
,.
""
tnjtct
""
"
,
.,
....
L
T_
l§
"
.....
""
.
........
Mao
..... ..J
"......,
o 'F
100
Fil. 21-Simplified SSB
~cei~r.
,
Thl:'re
are
only
minor
differenoes
be~ween
the
opera-
tion
of
an
SSB
receiver
and
a
ltandard
AM
reeei~r.
Fint,
the
f~uency
of
the
local oscillator
Mlleeu
the
upper
or
lower lideband.
The
block diagram
in
FIll".
21
shOWI
a
~ypieal
local oscillator arrangement.
The
LSB oecillator will
produce
a
diflerent
frequeney
of
7.8 MHz when combined with a
lower
lidtband
signal.
Thil
il
done
by
miIing
the incoming tlngle
sideband lilPlai
with
a frequency
of
about
19.2
MHz.
The
USB
c.eUlator
wiU
alao
produce
a 7.8 MHz
IF
frequency when
miud
with
an
upper
sideband lienal.
In this e.se, the injed.ed frequency is 34.8 MHz, 01"
7.8 MHs
abaft
the
selected
lideband
frequency.
The
IF Stagel pllU
the
lignal
as
an
ssa
signal.
It
it
necessary
to
re.insert the missing carrier
f~ueney
before final
detection.
This
i,
done
in a
"Product
Mixer"
which insertll the miMing
7.8
MHz carrier on
the
SSB
IF
aignal.
The
rellUlt
i,
an audio
output
that
is
the
same lIS the original
modulation
information
present
in
the
transmitter. In order for
the
carrier
mixer
to
operate
properly.
the
ill5l!rted signal muat be
EXACTLY
the
arne
frequency u
the
milling carrier.
The
"clarifier
control"
allo'Q
the
frequency
of
the
7.8
MHz oscillator
to
be
shifted
a1ighUy.
Thit
com·
penata
for.
tn.nsmitc.er
that
may
be
alighUy
off
frequency
(but
ltill
within FCC
spea).
FREQUENCY
SYNTt£SlZER
•
I
Some
trantcei....n require
one
cryH&I for
eldl
l.raJu..
mitter
channel
and
one for each
rt'*iv«
en.nnel..
Thill me&ruI a .23
dianne!
uamcei'ft!l"
requin'l
46
CfYsWI.
Plequency
synthesizer
stageI
reduce
the
number
of
CfYltaII
to
1<4
or
1_
for
aU
23
tranmlit
and
reeeive
-..,es.
A syntheli&er
tauladvantage
of
heterodyning-'II'hidl
prodUDeli
the sum and difference
of
two
oeeillator
frequencies.
By
selecting
the
frequenciell
of
two
oeeiJ·
laton
properly.
the
required 46 frequencies
can
be
obtained willi fewer
than
46
c:rystaill.
Mo,t
synthet1un
lIIe
t'll'O
oscillaton
which are fed
to
a
mlIer
Itage.The
out.put
of
the
mixer
ill then tiltered
to
produce
the
wm
or
difference frequency.
In
other
types
of
synthesizen,
a llIird
OICi1la~or
il
aim
used. Willi
Utili
leWp.
the
output
of
the
fin~
ee~
of
oscillators produces an intermediate frequency whieh
ill then mixed with
the
third OlIcillator
to
produce
the
final desired frequency.
CRYSTAL
SYNTHESIZER
SCHEME
Hon::
on
frequendel
m
'"
M!I%
•
~,<
~.
-
,~,
_.
._.
"
•
..
-
.-
--
,
'.-
'.'-
•.
-
u"
0.-
•
".-
...
-
N.""
..
'"
......
•
"
....
..
,-
.......
'.'"
"
....
•
.-
..
,-
N
......
...
..
......
•
n.'"
"'-
"."
..
'.'"
"
....
•
...
..
,-
.......
'-'II
".'"
•
...
-
.
..
-
....
-
,."
.
"
....
•
".'"
'.'-
....
-
'
....
"
....
•
..
-
...
".
..
.....
'.m
".'"
•
".-
..
,
...
".n
..
'.m
".".
"
,,-
...
".
..
,.-
,.m
..
....
"
u._
..
,-
.......
,.",
n
....
" ".'"
,.,,,,
..
,
....
..
'"
......
..
"
....
·"
...
..,
....
'.m
..
.U,
"
n
....
•
"~to.
0
...
..
'"
,..,,,
0
...
'"
,,'
...
..
.....
'-I"
...
".
••
n
....
,.""
..
-
,.
".
..
....
..
"
....
.
.....
..."
..
,.
m
".'"
"
n
....
,.""
...
"
..
,.
'"
".!II
"
......
'.,,"
.......
'.m
".'"
"
......
'.lI"
.......
'.m
".m
" ".'"
•.
lI"
".""
I.'"
".,n
"
......
'.lI"
n.""
,.",
".n'
Fig.
22-Q.ci/klcor
"..qUllnc/e.
or
J4
eryfial
tyn·
thuuer.
"
To Next Page
Loading...
Need help?
General
