the transmitter to about 10W.
Turn the calibration knob clockwise until the meter
pointer indicates the CAL position. Then, set the
function switch to the SWR position and SWR will be
indicated on the meter. Note that if the power of the
transmitter is less than 1W, the meter cannot be set
to the CAL position.
Also, when SWR is close to "1" during matching
work, the meter pointer will deflect little, making it
impossible to find the dip point of SWR. In this case,
turn the calibration knob further clockwise until the
meter pointer properly deflects so that the dip point
can be obtained for easy matching of impedance. The
reading of SWR obtained in this manner is incorrect
because the calibration knob has been turned beyond
its set point, so the meter should be calibrated again
according to the ab()vementioned procedure after the
completion of impedance matching.
The value of SWR measured on the meter varies
slightly with the volume of power, since the detector
diodes in the circuit have non-linear characteristics.
Normally, SWR should be calibrated at 10W of
forward power. If the power is larger than 10W, the
value of SWR on the meter will be a little higher than
the actual value, and vice versa. Accurate SWR can be
measured at 10W of forward power or by calculation
after measuring forward power and refrection power
as described below.
2. Measurement of forward power (FWD)
Connect the instrument as shown in Fig. 6. Set the
10
power range selector to the 150W position to prevent
the meter pointer from scaling out. Set the function
switch to the FWD position. With the transmitter
operated, adjust the power range selector to the
proper range and read forward power on the scale.
If a dummy load is connected to the ANn or ANT2,
instead of connecting an antenna, the instrument
functions as a terminal type power meter, allowing
you to check the operating condition of the antenna
being used by manipulating the antenna selector
pushbutton. It is also useful for tuning the trans-
mitter.
3. Measurement of refrection power (REF)
Set the instrument as described above except that the
function switch should be positioned to REF. Refrec-
tion power will be read on the meter scale.
4. Calculation of SWR from forward power (Pf) and
refrection power (Pr)
After the forward power (Pf) and refrection power
(Pr) have been measured according to the procedures
outlined in items 2 and 3 above, accurate SWR can be
obtained from the following equation:
1+ rP;
N~
1- {P;
Np'f
SWR=
'.
Actual SWR can also be obtained from the ratio of Pf
to Pr on a praph (Fig. 7).
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