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P A R T I
M O D E L 4 O O T R A N S C E I V E R
C I R C U l T T H E O R Y
GENERAL DISCUSSION
The Sr ran 400 Transceiver plovides siagle
s i d e b a n d , B u p p r e s s e d c a ! r i e r t r a n € c e i v e
operation; and generates the Bingle side-
band eignal by mean6 of a crystal lattice
filte!.
To permlt a logical diEcussion of
thi6 lnode of operation, certain definitions
ate nece€5aly,
In a normal AM signal
(double dideband with carrier),
a radio
frequency i6 modulated with an audio Jre-
quency signal.
This is considered by
many to be merely a ca8e of varying the
amplitude of the carlie!
at an audi.o rate.
In fact, howeve!, there are actual.ly side-
band frequencies generated which ale the
!eBults of mlxing the RI. and A!' 6ignal3.
These sideband3 are the suh ot, and the
difference between the two hetelodyned
6ignals.
For detection by means of
conventional diode detectols, the two
sidebands are mixed with the carlier
to
detect aDd to demodulate the audio
intelligence.
This inef{icient hean€ of
transrnis sion p€rrnits only approximately
25 per cent of the full tlanahitted
power
to b€ used to tras6lnit
intelligence.
There are other attendant drawbacks,
also.
The bandwidth of the transmitted
6igna1 is on the order of 6 kc, while the
actual dehodulated audio is 1e66 than
3 kc.
The lesult i. very limited use of
the band, and over half of the allotted
frequency range iB unuaable becauge oI
heterodyne6, ioterference,
and congestion.
In the single sideband, suppressed carlier
rrode of transhioeion,
only ono sideband
of the Rr. and AF heterodyned signal is
tranBmitted,
the other sideband and the
carrier
being Buppressed to a level which
effectively
permits
using only the audio
intelligence bandwidth.
This results in
increasing the transrnission efficiency
many times ove!, and pellnits an effec -
tive doubling of the use of the allocated
frequenciea.
It rnust be remerrlbered that in the single
aideband, suppresned calrier
mode of
transhission,
both the unn,anted side-
band and the calrier
ale oaly Buppressed,
not entile1y eliminated.
Thu6, with a
transmitted
sigDal frorn a transmittei
with 40 db sideband 6uppression,
the
other, or unwanted sideband is pleBent,
and it i6 transrnitted,
but its leve1 is
40 db below the'wanted sideband. When
3
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