EXAMPLE 2.
Assume unknown fx is approximately 1.1 GHz; Time Base = 1 ms.
a. Where f2 is lower than f1:
f1 = 110000 kHz (read on counter) tuning lower in frequency gives
f2 = 100000 kHz (read on counter)
f1 - f2 = 10000 kHz
N = 110/10 = 11.
Set thumbwheels to 11;
fx = 11 x 100000 = 1100000 kHz.
b. Where f2 is higher than f1:
f1 = 1100000 kHz (read on counter) tuning higher in frequency gives
f2 = 122000 kHz (read on counter)
f1 - f2 = 12000 kHz
N = 110/12 = 9
fx = 122000 x 9 = 1100000 kHz.
d. Verification of Harmonic Number N. The transfer oscillator method
of measuring frequencies higher than the counter's capability requires that
harmonic number N be known exactly.
Since there are many harmonics to
choose from, a foolproof method of verifying the selected harmonic number is
necessary.
In use, N is either increased or decreased by 1 on the
thumbwheel switches and the internal VF0 is returned for zero beat or phase
lock at an adjacent harmonic to match the change on the switches. Thus, the
measured frequency displayed is the same in both cases if the choice was
correct.
3.
CIRCUIT DESCRIPTION
This portion of the lesson is devoted to a circuit description of the
Model 5257A and is presented in two parts; the first is a block explanation
accompanied with a block diagram, and the second is a more in depth circuit
analysis.
Throughout the remainder of the lesson, refer to the block
diagram as well as the figures depicting the individual circuits.
a. Block Diagram Description. There are ten functional sections to the
Model 5257A. These are shown connected as a system in the functional block
diagram of figure 3. The frequency to be measured is applied to
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