
Model 8640B
TM 9-4935-601-14-7&P
manual's print date and part number, both of which
appear on the title page. Complimentary copies of the
supplement are available from Hewlett-Packard.
1-11. For information concerning a serial number prefix
not listed on the title page or in the Manual Changes
supplement, contact your nearest Hewlett Packard
office.
1-12. GENERAL DESCRIPTION
1-13. The Model 8640B Signal Generator covers the
frequency range 500 kHz to 512 MHz (450 kHz to 550
MHz with band over-range) and can be extended to
1100 MHz with an external doubler. An optional
variable audio oscillator is also available to extend the
CW output range of the generator down to 20 Hz. This
broad coverage, together with calibrated output and
modulation, provides for complete RF and IF
performance tests on virtually any type of HF, VHF, or
UHF receiver.
1-14. This solid state generator has an output level
range of +19 to -145 dBm (2 V to 0.013 MV) and is
calibrated and metered. The output is leveled to within
+0.5 dB across the full frequency range of the
instrument.
1-15. The generator also provides AM, FM, and pulse
modulation for a wide range of receiver test
applications. AM and FM can be performed
independently or simultaneously in either the internal or
external modes. This modulation is calibrated and
metered for direct readout under all operating
conditions. External pulse modulation is also available.
1-16. Other significant features are extremely low
noise, built-in phase lock and counter, and front panel
controls designed for operating convenience and
flexibility.
1-17. PERFORMANCE CHARACTERISTICS
1-18. Spectral Purity
1-19. The basic frequency source of the Signal
Generator is a mechanically tuned high-Q cavity
oscillator that operates over the frequency range 230
550 MHz. This oscillator has an inherent stability of
better than 10 ppm/10 min and exceptionally low noise
characteristics. The lower 9 frequency ranges are
obtained by dividing the basic oscillator frequency and
filtering the unwanted harmonics. Using this technique,
sub-harmonic and non harmonic-spurious are virtually
eliminated. A band over-range of 7% to 10% is also
provided for convenience when operating near the
nominal band edges.
1-20. Frequency tuning within the selected band is
accomplished with approximately 8 turns of the
FREQUENCY TUNE control (see Figure 3-2) for fast
selection of the desired output frequency. A mechanical
FINE TUNE control has a tuning range of 200 ppm for
precision frequency setting.
1-21. Restabilization time is short when tuning the
frequency across any one band. The total frequency
excursion after any frequency change is typically < 20
ppm and within 15 minutes the output has restabilized
to the specified 10 ppm/10 min. When not phase
locked, no restabilization time is required when
switching frequency bands for a fixed position on the
frequency tune control.
Figure 1-2. Measured Single Sideband Noise vs
Offset from Carrier. (Stated in a 1 Hz Bandwidth at
256 and 512 MHz Carrier Frequencies on 256 512
MHz Band.) Markers indicate specified limits.
1-22. Noise performance of the generator is state of the
art for a solid state generator. The high-Q cavity
oscillator has been optimized with use of a low noise
microwave transistor for a spectrally pure output signal.
Figure 1-2 shows the typical measured single-sideband
noise performance in a
1-2
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