Sensitivity (50 W source)
Equal to or better than
(Refer to equipment list)
Every 10 MHz
Every 100 MHz
Every 500 MHz
Every 1.0 GHz
Sensitivity is specified at the mixer input. Insertion loss through the cable, at the higher (GHz) frequency range, will become significant. Fig.
is a graph that shows
the approximate loss
in dB for
a 6 foot
When checking the sensitivity of scales 7 and 8, apply the source signal to the Waveguide Mixer, then connect the Waveguide Mixer to the
Mixer Adapter through the 2 foot cable with TNC connections.
do not exceed 2 divisions in amplitude. (2 average noise
25. Check Amplitude of Spurious Signals from
e. Move the 50 Ω termination to band B RF INPUT con-
Requirement-With the DISPERSION RANGE at kHz/DIV
nector and switch the band selector to band B. Change the
for band A, spurious signals must not exceed 2 times noise
DISPERSION RANGE to MHz/DIV and the DISPERSION to
bands B and C, spurious signals should be down more than
f. Adjust the GAIN control for an average noise level of
-40 dB with 100 kHz resolution.
1 division, then tune across the entire band, checking for
b. Connect a 50 W termination on band A RF INPUT
spurious signals greater than 2 divisions in amplitude.
connector and switch the band selector to band A.
g. Move the 50 Ω termination to band C RF INPUT con-
c. Set the DISPERSION RANGE to kHz/DIV, the DISPER-
nector. Change the band selector to band C.
SION to 500 kHz/div and the RESOLUTION control fully
h. Measure band C for spurious signals as above.
This concludes the performance check for the Type 491.
d. Adjust the GAIN control for an average noise ampli-
If the instrument has met all checks it is ready to operate and
tude of 1 division then tune the RF CENTER FREQUENCY
will perform to specifications listed in Section 1.
control across the entire band checking that spurious signals