HP 61 - Page 5

Appl. Note 61
691A/B
SWEEP OSCILLATOR
Page 5
130C
0OSCILLOSCOPE
0 Q
el (o) (o]
y ) x
—®
[ SWEEP RF
ALC
= 423A DETECTOR
423A DETECTOR WITH SQUARE-
LAW LOAD
PAD OR LOW-
PASS FILTER T A
AS REQUIRED -7
— - DEVICE
= UNDER
s o TEST
COUPLER ] sHORT
Figure 6. Setup for Reflection Measurements in Coax
690 SERIES 130¢
SWEEP OSCILLATOR
0SCILLOSCOPE
424A
DETECTOR o o
424n WITH OPO2
DETECTOR SQUARE-LAW
LOAD -
SWEEP RF L
ALCH J
PAD OR LOW-
PASS FILTER v
AS REQUIRED -
X X e DEVICE
- UNDER
281A
ADAPTER
T
cvee
o
TEST
(NOT REQUIRED T
ABOVE 12.46C) COUPLER COUPLER =[] suort 4000-8-3
Figure 7. Setup for Reflection Measurements in Waveguide
With Sweep Oscillator Power Switch in "STANDBY"'.
- Adjust sweep oscillator frequency limits.
- Set oscilloscope horizontal gain control to give the
desired calibration inGe/cm. The sweep oscillator
sweep circuits mustbe operating for this adjustment.
For use with "SWR'' scales shown in Table III, set
the oscilloscope vertical position control to estab-
lish the CRT trace exactly 3 cm up from the grati-
cule center line. This corresponds to 1.00 on all
SWR scales.
With Sweep Oscillator Power Switch in "RF"".
- Place short on reflectometer.
- Adjust sweep oscillator for leveled sweep as dis-
played on oscilloscope.
- For use with SWR scales shown in Table III, set os-
cilloscope vertical attenuator and vernier controls
to establish CRT trace exactly 3 cm below graticule
center line. This corresponds to = on SWR scale
and 0 db return loss on db scale.
Remove short from reflectometer and with system
open -circuited, observe =-SWR - reflection/0-db
return-loss-line on face of CRT. Phase reversal
will be about 180°, but amplitude deviation should
be about the same. If a substantial difference exists
between the calibrationlines obtained with the short
and the open, there is a fault in the measurement
system which should be corrected. For return loss
differences of less than +1/2 db use a calibration
setting halfway between the ''short'" and"open' trace
lines.
YOUR AMPLITUDE AND FREQUENCY SCALES
ARE NOW CALIBRATED FOR MEASURING RE-
FLECTION IN SWR.