Section 11 Model 683C
Paragraph 2-8
the bwo will be operating over a small section of the
helix voltage-vs-frequency curve and the curve can be
considered a straight line. If, however, large modu-
lating voltages are used, the bwo will be operating
over a large section of the helix voltage-vs-frequency
curve and the curve is exponential. When the modu-
lating voltage is large, a shaping circuit may be used
which provides an exponentially-varying voltage which
has a helix voltage-vs-input-voltage curve which is
the same shape as that of the bwo helix voltage-vs-
frequency curve.
CAUTION
The bwo can be damaged if the 683Cis swept
out of its rated band (2 to 4 kmc [gc]). The
possibility of sweeping outside the band is
greatest 1) when a wide band is swept (volt-
5 10 20 50 100 150 RO
age excursions applied to the FREQ. MOD. MODULATING VOLTAGE (PEAK-TO-PEAK)
jack are greater than 150 volts peak-to-peak)
and 2) when the FREQUENCY dial is set Figure 2-8. Allowable External Frequency
near one edge of the band. Modulation Voltage Amplitude vs
Modulation Voltage Frequency
To guard against sweeping outside the band,
the arrangement shown in figure 2-9 may be
used. The output from the 683C is applied
through an attenuator, two wavemeters, and reflection or swr with a reflectometer, but often over-
a crystal detector to the vertical input of an looked is the fact that a reflectometer or ratio meter
oscilloscope. The modulating voltage is is equally valuable for measuring attenuation, gain,
applied to the oscilloscope horizontal input. and other transfer characteristics over a wide range
and in rapid fashion. The ratio meter system is also
Each wavemeter is tuned for one edge of the good for measuring the magnitude of scattering matrix
band. Thus, as the band is swept, a wave- coefficients when it is desired that a transmission-line
meter pip at each end of the oscilloscope network be described in terms of such coefficients.
trace will define the rated range. and any
Information regarding this type of measurement using excursion beyond limits can be ietermined.
the 683C is found in Hewlett-Packard Journal Sept.-
Oct. 1957, Volume 9, No. 1-2 (Permanent Record and 2-8. APPLICATION.
Oscilloscope Techniques with the Microwave Sweep ,
One of the valuable uses for a microwave sweep oscil- Oscillator); Hewlett-Packard Journal Dec. 1960, Vol-
lator lies in its ability to permit rapid measurements ume 12, No. 4 (Improved Sweep Frequency Techniques
of microwave device performance over a range of for Broadband Microwave Testing); Application Note
frequencies. One example is the measurement of 42 (Applications of the 416A Ratio Meter).
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