HP 61 - Page 6

Page 6 Appl. Note 61
Table III. Examples of Transmission and Reflection Scales for Use on Cathode-Ray Tube Graticule.
Use transparent plastic or white-paper inserts provided with this Application Note
for calibration of CRT face.
db SWR SWR SWR SWR SWR
[rp— 1.00 -1 1.00 1.0 1.00 1.0 1.00 - 1.00 1.00 - 1.00
L] 2 1 i 1.05
7.8 7°° 2.38 130413 120412 w2 b9 1.085 4-1.08
2
3
110
6.0 14 115
48 373 145 130413 118 1122
4.0 4 15 1.20
30430 58S 1584 16 1384, 122 Lis2 115
8 2 i1
1842° 99f0 1707 145 g g 2> IATE SRT
osf 0 224-20 181 1.8 PO 130 4 1.30 120 4-1.20
olo ol w--0db odb 1.58 J-—-13db 1.33{---17db 1224 1.22--20db
135
204 +20
MEASUREMENTS
Place the unknown device under test as a termination
onthe reflectometer. Change the oscilloscope vertical
step-attenuator setting to bring the trace as close as
possible to (but still above) the lower 3-cm calibra-
tion line, without changing the vernier or vertical po-
sition controls. If more vertical amplifier gain is
required, use the 140A Oscilloscope with 1400A and
1420A Plug-In Units.
B 1 |
1.45 1.50
Frequency in Gc
1.35 1.40 1.55 1.60
Figure 8. Reflection from Coaxial Crystal
Detector Mount (older style)
Note the number of steps traversed by the step-atten-
uator and from Table I relate to return-loss in db.
Knowing return-loss, select the matching SWR scale
from Table III. Full scale (6 cm) return-loss is
marked on each SWR scale. Cut the proper trans-
parent
"SWR'' scale from the foil. Place scale on
oscilloscope graticule as shown in Figures 8 and 9.
Use either static charge or several small spots of
rubber cement to hold scale in place. The thus se-
lected reflection scale gives an accurate calibration
of SWR on the CRT face.
*)
1.35 1.40 1.45 1.50 1.85 160
Frequency in Gc
Figure 9. Reflection from New Flat-Response
423A Coaxial Crystal Detector Mount
(note low SWR)
The examples shown in Figures 8 and 9 display sweep
reflection measurements for two coaxial crystal de-
tector mounts. The older mount design measurement
shown in Figure 8 indicates a SWR of 1.65 to 1.75,
with a 10-db return-loss line. Measurement on the
mount of newer design shown in Figure 9 indicates a
SWR of 1.14 to 1.15, with a 20-db return-loss
reference.
RECOMMENDED INSTRUMENTS
Both coaxial and waveguide instruments for leveled
swept frequency measurements are shown in Table IV.
Attenuators for making insertion and return-loss cali-
brations are indicated. Hewlett-Packard sweep os-
cillators and other instruments shown give complete
coverage from 1 to 40 Ge.