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Heathkit HM-2102 - Page 21

Heathkit HM-2102
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Page
17
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FIBATHEITS
To
obtain
total
losses
in
a
given
length
of
coaxial
cable,
determine
the
dB
loss
per
foot
of
the
cable
from
Figure
4.
This
is
done
by
finding
your
operating
frequency
on
the
bottom
line
of
the
chart,
and
moving
up
to
find
the
type
of
cable
used.
By
looking
at
this
same
level
on
the
left-hand
side
of
the
chart,
you
can
read
the
dB
loss
per
100
feet
of
the
cable
at
that
frequency.
Now
determine
the
additional
loss
caused
by
the
SWR
from
Figure
5
as
follows:
Use
the
amount
of
loss
determined
from
Figure
4
and
find
this
value
on
the
bottom
line
of
Figure
5.
Now
move
up
the
graph
until
you
come
to
the
SWR
of
your
antenna
system.
Move
over
to
the
left-hand
side
of
the
graph
and
determine
the
amount
of
loss
caused
by
the
SWR.
To
obtain
the
total
loss
of
your
system,
add
the
value
from
Figure
4
to
the
value
from
Figure
5.
Multiply
the
total
loss
by
the
cable
length
in
feet.
Then
divide
by
100.
Loading
The
load
presented
to
the
transmitter
output
circuit
may
create
conditions
that
make
it
touchy
or
impossible
to
load
the
transmitter.
With
a
low
SWR,
the
load
that
the
transmitter
sees
is
practically
pure
resistive.
However,
at
a
high
SWR,
the
apparent
load
may
change
from
a
very
low
to
NORMAL
ATTENUATION-COAXIAL
CABLES
vs
FREQUENCY
'0
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LC
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5
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ald
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ay
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6
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xe
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|
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a
110
fer
t4-+
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4
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4
4
+
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a
03
4
—-
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a
02
1
2
3°94
5678
10
20 30
40
5060
40
100
200
FREQUENCY
IN
MEGAHERTZ
Figure
4
a
very
high
resistance,
accompanied
by
either
capacitive
or
inductive
reactance.
These
resistance
and
reactance
values
change
when
the
transmission
line
length
or
frequency
is
changed.
Remember
when
you
are
using
50
2
nominal
unbalanced
feed
lines
that
the
SWR
cannot
be
changed
by
changing
the
transmission
line
length.
However,
the
loading
to
the
transmitter
may
be
changed
considerably;
thus
making
it
appear
that
“‘pruning’’
the
cable
length
offers
improvement,
when
it
actually
does
not
affect
the
SWR.
The
SWR
can
only
be
changed
by
changing
the
toad
or
termination
at
the
cable.
If
the
transmission
line
length
is
changed,
for
example,
with
50
Q
cable
and
an
SWR
of
3:1,
the
apparent
load
to
the
transmitter
may
vary
from
16-2/3
2
to
150
Q
resistive
in
series
with
reactance
varying
from
66-2/3
2
capacitive,
to
zero,
to
66-2/3
Q
inductive.
If
the
transmitter
output
tuning
adjustments
will
not
accommodate
this
impedance
range,
the
transmitter
will
be
difficult
to
load
until
the
load
is
properly
matched
to
the
line.
When
the
load
is
matched,
the
SWR
will
be
low,
approaching
1:1.
This
condition
provides
the
greatest
accuracy
for
Power
Meter
measurements.
POWER
METER
The
operation
of
the
Power
Meter
is
simple.
A
load
must
be
connected
to
the
output
jack
of
the
Meter.
Merely
place
the
FUNCTION
switch
in
either
the
25-
or
250-watt
position;
then
read
the
corresponding
scale
on
the
meter
scale
to
obtain
the
power
output
of
the
transmitter.
SWR
ATTENUATION
19
T
LT
8
++—-+
|
7
20
RB
6
ES
7
ee
+
+
mee?
4
PER
100
FEET
ADDITIONAL
LOSS
IN
DB
CAUSED
BY
STANDING
WAVES
.
L}
2
3
4.4
8
6
7.8.9.0
2
3
4
5678910
LINE
LOSS
IN
DB
WHEN
MATCHED
Figure
5

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