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.
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
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
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
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