d. Turn the 20 dB ATTENUATOR switch for the Type 491
to the ON position. Adjust the variable output attenuator
on the signal generator for an approximate 3 mV display
amplitude on the test oscilloscope.
e. Adjust L147 (Fig. 6-39), the 65 MHz trap, for minimum
response to the 65 MHz signal.
f. Remove the signal generator signal and the test os-
cilloscope connection. Reconnect the Sealectro connectors
and cables to J120 and J188.
9. Apply a calibrated signal within the frequency range of
band B through a 20 dB attenuator (Part No. 011-0086-00)
to band B RF INPUT connector.
h. Set the Dispersion to 10 MHz/div. Tune the RF center
frequency to the applied signal frequency. Adjust the
MIXER PEAKING for maximum signal amplitude. Adjust the
GAIN plus the variable attenuator of the signal generator
for a signal amplitude of 6 divisions.
i. Calibrate the output amplitude of the RF signal from
the signal generator.
band and check the response flatness of the Type 491. Signal
amplitude should not vary over 1.5 dB, or a total of 3 dB
from the maximum to minimum amplitude point, with a
constant amplitude input signal to the RF INPUT connectors.
Adjust the MIXER PEAKING for maximum signal amplitude
for each display window.
NOTE
This is not a conclusive check because the local
oscillator power may vary over this frequency
range. Try other input frequencies and oscillator
frequency ranges.
k. If the response flatness is not within tolerance, adjust
C137 and L134 (Fig. 6-39) for optimum sensitivity and flatness.
Adjusting C137 will produce a noticeable affect on the
response slope. Adjust L134 for optimum sensitivity at the
high frequency end of the response.
l. Increase the signal generator frequency to 800 MHz
bration. These filters require special test equip-
and tune the Type 491 to this frequency.
ment and technique to calibrate. Contact your
local Tektronix Field Office or representative.
m. Adjust the MIXER PEAKING control for maximum
This procedure does not require a Sweep Gener-
signal amplitude.
ator, however, a Sweep Generator such as the
Kay Model 121 C Multi-Sweep Generator may be
n. Adjust C68 (Fig. 6-39) on the band B RF mixer for
used to check flatness.
optimum sensitivity and bandpass flatness. Tune the signal
across the screen with the RF CENTER FREQUENCY control
a. Equipment setup is given in Fig. 6-38.
to check flatness.
b. Disconnect the cable connector from J120 on the honey-
comb assembly and apply a calibrated 65 MHz signal (--30
o. Check the display flatness over the frequency range of
dBm) from the signal generator to J120 as described in
the instrument as follows:
step 23.
NOTE
c. Disconnect the cable connector from J188 (output of
Each time the signal generator frequency is
the IF Attenuator). Connect the output of J188 through a
changed it will be necessary to recalibrate the
subminiature to BNC adapter and coaxial cable to the Verti-
output amplitude.
cal connector of the test oscilloscope.
6-37
