HP 3048A Operating Manual page 177

Table 3-25. Numbered Error Messages (10 of 17)
7 4. If the Frequency Intervals vary greatly and are considerably larger than expected for
(cont'd)
t n e
tuning range of the the VCO, then:
• Check for erratic frequency drift of the beatnote. (Beatnote stability is
directly related to the frequency stability of each signal source used in the
measurement.)
5. If all four measured frequencies are 0 Hz, then:
• Check for injection locking. Refer to Minimizing Injection Locking in Chapter 3
of this manual for further information.
8
Unable to find a beatnote. System was not able to detect a beatnote above -24 dBm
(20 mVpk) between 0.1 Hz and 40 MHz.
Action: Verify the presence of the beatnote signal. (Refer to the Checking the Beatnote
procedure provided in each Phase Lock Loop measurement example in Chapter 3 of this
manual.) If you are making a Phase lock loop measurement, be sure the VCO Tuning
Constant value entered for the measurement is within a factor of 2 of the actual value.
Refer to the HP 3048A Reference Manual Calibration Process in Chapter 2, Measurement
Definitions for information about the beatnote calibration technique.
The calibration spur could not be found. The system was unable to detect a spur
within a factor of 2 of the entered spur frequency.
Action:
1. Check that the correct spur frequency was entered.
2. Verify the output signal from the spur source.
3. Increase the spur level up to but not exceeding a maximum of —20 dBc.
NOTE
If a single sided spur is being used and the source frequency is adjusted to
maintain quadrature, the frequency of the spur source will also have to be
adjusted to maintain the desired spur offset.
" | 0 Waveform departs too drastically from sinusoidal to be used in calculation of
the Phase Detector Constant. The system measures the slope of the waveform at
both the positive and the negative zero crossings. If the true slopes differ in magnitude
by more than 10%, Error 10 is generated.
Action: Check the harmonic content of the two input signals to the Phase Detector. All
even harmonics must be below -20 dBc to guarantee good symmetry of the beatnote
waveform. If possible, increase the PTR to >10 kHz so that the beatnote is >1 kHz.
Then the HP 3048A will measure the fundamental and its harmonics. (<1 kHz beatnote
system measures slope of sinusoid.)
3-130 Signal Source Applications
rev.l2JUL88