Heathkit SB-10 - Page 4

FIIEI
f9.
a
given
ampli-fier
peak
power
rating,
by
eliminating
the
carrier,
we
can double
the
amplitude
of each
sideband,
This
increases
the
total
sideband poier
(1+1)2
o;'4
limes.
Referring
to Figure
I' it
is
apparent
that
each sideband
of
a l00To
amplitude
-oauf.t"a
"r""ier
is
one
half
the
amplitude
of
the
carrier
or, squaring
once
aga.in,
l/ 4'the
carier
powu".
-
rotrr
sideband
power
is
7/4 +,t/+,
or
7/2
the cariie"
piower.
N"otice
that
the
peak
power
rating
of the
l007o
amplitude
modulated
amplifier
,i-s,
"equal.
to the
power
at the
instint
df the
vottage
elements
of
Figur^e..l
add.
This is
equal
to
(2)z
or 4 times
ihe
carrier
power.
Thus,
by further
eliminating
one-of
the
two sidebands,
we can double
the
total
sideband powe.
once
rg.i"
-d still not
over-
load
the
amplifier
on
peaks
(4
x 2
x l/z
carrier
power
=
4
x
carrier
p'ower),
since
the
total
sideband-
power
is
multiplied
8 times,
an
increase
in
"talk-power"
of 9 db
is realized.
Srr-n4
by
eliminating
the carrier,
rve
eliminate
the
eRM
caused
by
"r..lu"
t
"t.oay.,u".
I+i4L
spectrum
space
is conserved
since
only
half
of the
original
afvr
"p""i""."
is required.
Ihf_l!"o
enables
the operator
to cut his receiver
bandwidth
in
"half,
furth'er
."drr".r,g
exposure
to
QRM.
SSB
operation
presents
two
primary
obstacles,
onephysical
and
the
other
psychological.
Siabie
oscillators
for
transmitting
frequency
control
and
carrier
insertion
atthe ieteive"
are a
prime
requisite.
This
problem
can b€
overcome
by
proper
design
and
has
been
solved
by the manu-
facturers
of receivers
and
SSB
transmitting
equipment producing
for
today's market.
The
supposed
complexity
of sSB
equipment
is the
psyctrologicai
obstacte]
nowever,
there is
nothing
about
SSB
_circuit
thmry
and
equipment
that
cannot
be easily grasped
by
the
average amateur
after
alittle
study
of
the numerous
articles
and
books
puUiinea
on
ttre"sublect.
Most
of
the
basic
circuits
are
familiar
and
only
vary in
their
application.
{fhe
initial
investment
in SSB
equipment
for
low
power
will
be somewhat
more
than
for
comparable power
AM
equipment.
Despite
this,
more
effective
communication
will
be realizea
wittr
ttre
'SSB
equipment
at the
same
power
level' Furthe.rmore,.
the investment
required
to
go
to higher
powLr
will
always
be considerably
lower
for SSB
equipment
since
no
highlevel
moaiutation
Equipment
ts
necessary.
The
principles
involved
in ssB
transmission
have
been
known
for many years,
but the Iack
of
commercially
available
sharp
cutoff.filters,
high
stability
crystals,
anO
audio
phase
shift
net-
worksrestricted
SSB
application
to relativelyfew
fields,
primarily
longdistance
ielephone
work.
Howevbr,
with
the radio
frequency
spectrum
becoming
more
and more"
crowded, some
services
began
to use
ssB
as
a means
of
conserving
availablelpace.
The
military
red
ihe way to more
widespread
use
of
SSB.
The FCC
then began
to order
other
services
to cbnvert
to SSB
and the
ensuing
transition
in
recent years
has not
only
stirred
up significant
amateur
interest but
also
brought
about
the
commercial
availability
of components
fbr SSB
equipment
at
reasonable
prices.
Two
methods
of
generating
an ssB
signal
are
commonly
employed
in
amateur
equipment. one
method
employs
very sharp
filters
of
either
the LC,
crystii
oi
mechanical
typ'e to
pass
one
sideband
and suppress
the other.
These
filters
exhibii
best
characteristics
at
lower frequencies.
Therefore,
filter
type SSB
transmitters
employ
heterodyne
methods
of converiing
the
low
ssB
frequency
to
the desired
band.
The filtering
method
hai
the
advantage
that frequency
stability
is
easier
to
obtain
at lower
frequencies.
Its
one
disadvantage
is
Jomplex
fii'ter
Oesign
and
adjustment
plus
somewhat
higher
cost.
Carrier
suppression
is
obtained
through
the use of
a
balanced
modulator.
The
phasing
method
of SSB
signal
generation
is
more
complex
in
theory
than filtering,
but has
the distinct
advantages
of lower
cost, easier
adjustments,
plus
equally
gooa pe"to"mance
at aII
frequ-encies.
Since
the
phasing
method is
employed
in
the SB-10
it
wiil be
explained in some
detail.
The
phasing
method
of
generating
a
single
sideband
vector
diagrams
and
then
referring
to
a
simplified
practically
applied.
signal
can
best
be explained
using
two
simple
schematic
diagram
to
see
how
the method is
Before proceeding,
it
may
be advisable
tobecome
re-acquainted
withvector
algebra.
euantities
which repres_ent
magnitude
only, such
as inches,
cubic
feet,
or degrees,
a"r e
called
scalar
quantities
and
can be
represented
merely
by
numbers,
However,
qu--ti
us which represent
PaEe
4