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Peak envelope
power is seen only
on a peak reading
meter. Average power
is seen on a
non-peak reading
meter, like a
standard Bird 43.
Pure 100% linear
undistorted sine
wave amplitude
modulation has the
following power
relationships:
Carrier power is 25%
of peak envelope
power, or if you
prefer peak envelope
power is 4 times
carrier power. A
1000-watt carrier is
4000 watts PEP with
undistorted 100%
sine wave
modulation.
Average modulated
power output is 150%
of carrier power.
This is because
average audio
modulation power is
50% of carrier
power. A 1000-watt
carrier is 1500
watts average power
when 100% modulated
with an undistorted
sine wave.
RMS
RF antenna current
is 1.225 times
unmodulated RF
carrier current. A
1000-watt
transmitter into a
50-ohm load is about
4.5 amperes
unmodulated carrier
and 5.5 amperes load
current when 100%
modulated.
Peak
RF output voltage
when modulated is 2
times unmodulated
carrier voltage. A
1000-watt carrier
into 50 ohms is
about 326 volts peak
voltage and 652
volts peak when 100%
modulated.
Thinks that arc,
like capacitors,
must be rated at
peak voltage. Things
that heat are
generally rated
using RMS current or
average power.
Amplifier Class
I’m not sure why
CB amplifiers are
called “AB1”. Any
tube amplifier with
grid current is not
“AB1”, it is either
class AB2 or class
C. Most CB amps are
actually class C,
and there is a
reason for that.
Solid-state
amplifiers cannot be
class “AB1” or
class “AB2”. A
bipolar transistor
amp cannot be a sub
1 or sub 2 class
because they do not
have grids to have
or not have grid
current. Solid-state
amplifiers have
bases or gates, and
a bipolar transistor
always has base
current.
Most CB amps are
intentionally
self-biased in at
least one stage with
some form of
unregulated bias or
supply voltage. This
causes them to
automatically adjust
gain to compensate
for differing drive
powers. The primary
objective is to
not be
linear. A linear
amplifier will not
“swing much” with
modulation, while a
grossly non-linear
amp will “swing”
substantially with
AM voice peaks.
Generally the way CB
amplifiers obtain
swing is through
class C biasing.
While they often
rest in conduction
with no drive,
giving the
appearance of being
class AB or B, they
develop self-bias
through a grid leak
(or base leak) that
pulls them into
class C when enough
drive power is
applied. A capacitor
across the leak
resistance averages
the bias voltage.
This establishes
gain at the point
where output power
is folded back far
below the point
where it would be
with stiff bias. It
is a form of slow
time constant gain
compression that
sets the carrier
level far below the
modulation peaks.
When an audio
peak comes along
they conduct
heavily, causing a
power meter to dance
upward on voice
peaks.
Another trick was an
unregulated screen.
They would get the
unregulated screen
wiggling around to
accent any power
change, and this
would cause carrier
shift.
It actually would be
pretty tough to sell
a real linear amp to
a CB op, because it
wouldn’t have that
great audio caused
by RF compression or
clipping. Most amps
were intentionally
or accidentally
built to be RF
speech processors.
Contrast that to a
real linear SSB amp.
In almost any real
linear amp bias is
very stiff. It is
regulated. The
screen voltage is
stiff also, up to
dissipation limit,
in a good clean
amp.
Class AB does not
mean the amplifier
is linear. “Linear”
in the context of
amplifiers indicates
a linear transfer
function, or a
transfer function
that has the proper
transfer function
curve shape to
minimize odd-order
intermodulation
products. A linear
transfer function
generally means the
output power level
tracks the input
power level in a way
that does not cause
excessive 3rd, 5th,
7th and other
odd-order mixes.
Only odd-order
mixing or distortion
produces annoying
splatter.
Often the criteria
is how the “audio
sounds”. The
on-frequency sound
tells us nothing
about bandwidth and
nothing about
harmonics.
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