23
Frequency Menu
The frequency of the FS700's FREQUENCY OUTPUT is set in the
FREQ menu. This frequency is set using the cursor keys in a 1, 2.5, 5
sequence (for example, 1 kHz, 2.5 kHz, 5 kHz), between 0.01 Hz and
10 MHz. This output has the same accuracy as the 10 MHz sine wave
outputs on the rear panel.
Phase Menu
The FS700's Phase menu allows the measurement of frequency
differences between the FS700's internal clock and the OSC IN BNC.
The measurement may be made with a 1 sec duration, or in a
continuous mode where the frequency difference is displayed for any
elapsed time up to 32767 hours.
The first screen of the Phase menu displays the output of the FS700's
analog phasemeter. This phasemeter measures the phase difference
between the signal at the OSC IN BNC and the FREQUENCY
OUTPUT BNC. These signals may range from 100 kHz to 10 MHz.
The FREQUENCY OUTPUT must be set to the same nominal
frequency as the input signal. The PHASE OUT BNC produces an
analog voltage that is proportional to the phase difference between the
OSC IN signal and the reference. The coefficient of proportionality is
0.01 V/degree (±3.6 V full scale). The output is digitized with a 8 bit
A/D converter, limiting the resolution to 3° for a 1 sec measurement.
The analog output is, of course, continuous. The FS700 can measure
any frequency offset up to 100% of the reference frequency, but the
analog phase output only functions to about 1 kHz offset.
The PHASE between the two signals is displayed in degrees. The
range of this number is 0 to ±360 degrees. The phase will be greater
than zero if the OSC IN frequency is greater than the reference, and will
be less than zero if the OSC IN frequency is less than the reference.
This displayed value is simply the digitized version of the analog
PHASE OUT signal.
dF displays the fractional frequency offset (df/f) of the input relative to
the reference. This calculation is made by doing an 1 s measurement
of the input frequency. The largest offset that can be measured is
100% of the reference frequency (dF = 1.0 E 0). The smallest offset
that can be measured is limited by the FS700's 3° phase digitization
resolution. For example, an offset of 3°/s at 10 MHz corresponds to a
frequency offset of 8 x 10
-10
.
The bar graph display shows the current phase in the form of a bar
graph. This display has a range of ±360°. The bar graph can be used
Frequency Out: 2.5 MHz
Phase: 109°
dF = 5.6 E-7
-360
+360
