Bird Model 43 Wattmeter
8
The simple relationships:
and
Note:
Where r = VSWR and f = Wr / Wf
These can be used to convert between the standing wave ratio (
ρ)
and the reflected/forward power ratio
(φ)
, which can be directly read
from the Thruline Wattmeter. The relationship between
ρ
and
φ
is
graphed in Figure 4 and Figure 5.
Note:
Attenuation, measured in dB, can be derived from
the power ratio by the equation N
db
= 10 log
φ
.
VSWR scales and their attendant controls for setting the reference
point have been intentionally omitted from the Bird 43. Experience
using the Thruline Wattmeter for transmitter tune-up, antenna
matching, etc. will show that the power ratio measurement is as use-
ful in practice as the standing wave ratio.
A trial is suggested – forget about VSWR for a few days and think
in terms of
φ
= W
r
/ W
f
. The two meter readings, W
r
and W
f
, give
a useful, approximate picture of the results without bothering to cal-
culate the power ratio exactly. Consider that, for an antenna match-
ing problem, the main objective usually is to minimize W
r
. Anything
done experimentally to this end will be seen when the element is
turned to the reflected power position.
ρ
1
φ
+
1
φ
–
----------------
=
φ
ρ
1
–
ρ
1
+
------------
2
=
Содержание Thruline 43
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Страница 37: ...Bird Model 43 Wattmeter 23 Figure 9 VSWR Conversion Graph Reflected Power 0 2 20 0 ...
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Страница 40: ...Bird Model 43 Wattmeter 26 Figure 11 Cable Length Wavelength Matching ...
