Section III Model 240A
Paragraphs 3-18 to 3-35
3-18. Set the SWEEP WIDTH control about half way TYPE 240-A OSClLLoSCOPE
1501-8 CABLE 1
to maximum, turn the CRYSTAL MARKER switch on, I RF OUTPUT- 1 h 1
and advance the CRYSTAL MARKER AMPLITUDE.
Birdie-type markers should appear on the oscillo-
scope. The number of markers depends on the mar-
ker separation and the SWEEP WIDTH setting.
I I IF I II .
3-19. TEST SIGNAL AMPLIFIER. I I' 1 r/
I /
3-20. An audio frequency signal of approximately Figure 3-3. Test Setup Using 501B Output Cable
1/2 volt applied to the TEST SIGNAL IN jack should
appear at the COMPOSITE SIGNAL OUT jack as ap-
proximately 4 volts with the TEST SIGNAL-
AMPLITUDE control turned full on.
3-21. AMPLITUDE MODULATION.
3-22. Connect a diode detector circuit across the
terminals of the 501B Output Cable and connect the
rectified output to the vertical input of the oscillo-
scope. Turn the RF LEVEL controls for full out-
Figure 3-4. Test Setup Using 501B Output Cable
put, the function selector knob to CW, and the AM
and 509B Output Cable
knob to ON. Adjust the internal linear sweep of the
oscilloscope for about 100 cps. The rectified
1000 cps amplitude modulation should appear on the
3-29. RF OUTPUT.
oscilloscope.
3-30. The RF output is obtained from the terminals
3-23. RF BLANKING AND FLATNESS.
of the 501B cable, which presents a source imped-
ance of 25 ohms. The open-circuit voltage, acting in
3-24. Use the diode detector and oscilloscope con-
series with 25 ohms, is indicated by the combination
nections of paragraph 3-22 with the oscilloscope
of the meter and the RF LEVEL FULL SCALE dial.
sweep rate set to 20 cps. Turn the CW-SWEEP
An additional 25-ohm series resistor must be placed
selector knob to SWEEP and turn the SWEEP WIDTH
between the high terminal of the 501B cable and the
control up about half way.
input to a 50-ohm receiver.
3-25. The oscilloscope waveform is shown in
3-31. TEST SIGNAL IN.
Fig. 3-2. The top line (demodulated RF) and bottom
line (base line) should be parallel and flat.
3-32. The detected output voltage of the circuit under
test is fed to the TEST SIGNAL IN jack.
3-33. SWEEP OUT
3-34. The SWEEP OUT and GND terminals are con-
nected to the horizontal input of the oscilloscope.
3-35. The SWEEP WIDTH control determines the
frequency deviation about the indicated center fre-
quency. (See Sweep Range in Table 1-1.)
NOTE: The system used for deviating an RF
signal about a center frequency depends upon
Figure 3-2. RF Sweep Flatness changing magnetic flux acting upon ferrite
cores in the RF oscillator coils. The cen-
3-26. USING THE SWEEP SIGNAL ter frequency, as indicated by the frequency
dial, is determined by the current in a coil
GENERATOR.
which is magnetically coupled to the ferrite
3-27. For use as a conventional CW or Amplitude core. Residual magnetism in the ferrite
Modulated Signal Generator, the only connection re- and iron cores can cause the center frequency
quired is the 501B RF Output Cable. calibration to be slightly off. Rotating the
SWEEP WIDTH control fully clockwise and
3-28. Figures 3-3 and 3-4 show typical arrangements then counter-clockwise will effect the
of test equipment for measuring the pass-band of a degaussing of the cores and return the in-
radio frequency amplifier having its own detector. strument to proper calibration.
3 -4 |
ACEC
