2
Chapter 2
Theory of Operation
Loads
convert
RF
energy
into
heat.
This
heat
must
be
quickly
transferred
to
the
surrounding
environment
to
prevent
damage
to
the
load.
The
coolant
fluid
surrounding
the
resistor
transports
the
heat
to
the
radiator
walls
by
convection.
There,
air
passing
over
the
radiator
fins
carries
the
heat
away.
When
a
load
or
attenuator
is
mounted
on
the
Bird
Blower
Assembly,
baffles
cover
the
radiator
fins
so
that
the
high
airflow
generated
by
two
blower
fans
is
confined
to
passing
over
the
fins.
Up
to
twice
as
much
RF
energy
can
be
dissipated
by
this
forced
draft
air
flow
as
compared
to
normal
convection
air
currents.
Thus,
a
2.5
kW
load
will
safely
dissipate
5
kW
using
the
Bird
BA–300/310.
Power Rating Reduction
The
baffles
interfere
with
the
free
flow
of
normal
air
currents,
causing
a
50%
reduction
in
heat
transfer
efficiency
if
the
forced
airflow
is
stopped.
Thus,
a
2.5
kW
load
will
have
its
maximum
power
dissipation
reduced
to
1.25
kW.