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Agilent
8645 Signal Generator
Communication
Product Note 8645-2
A catalog of 8645A information
This product note is actually a has to offer and the performance of the topics are covered in great
compilation of many brief prod- it can provide. The objective of detail and other literature may
uct notes, each concerned with a this product note is to be a refer- offer a more thorough treatment
particular aspect of the 8645A ence guide for the owner of a of a subject, these summaries
agile signal generator. Included 8645A, to help maximize the use- should provide sufficient infor-
in these pages are explanations fulness and performance of this mation to help in many situa-
of how this unique signal genera- agile signal generator in the tions.
tor operates, the capabilities it intended application. While none
Table of contents
Operation related topics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Block diagram and theory of operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Timebase configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Internal audio source. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Frequency sweep capabilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Externally doubled outputs to 2060 MHz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Operation as a phase noise reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Programming with HP-SL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Command sequence independence using HP-SL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Performance related topics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Phase noise performance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Spurious performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Third order intermodulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Divided outputs below 515 MHz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Stereo separation quality. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Minimizing fan noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Frequency agility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Functional description of frequency agile operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Faster frequency switching using multiple agile generators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Frequency accuracy of agile outputs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Relating phase error and frequency accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Amplitude dynamic range while frequency hopping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Amplitude shaping of agile outputs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
High rate, high deviation FM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Simultaneous modulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Digitized FM operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
AC coupled FM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Special capabilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Tailored operation through special functions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Protecting classified instrument settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Storage registers and sequential recall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Offsets and multipliers of frequency and amplitude . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Built-in calibration functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Finding failures with internal diagnostics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
2
Operation related topics
Block diagram and theory
of operation
The basis of the 8645A is a sin-
gle fractional N loop controlling
plished in the output section Besides high performance out-
a VCO operating in the frequen-
through control of the Automatic puts for traditional applications,
cy range of 515 to 1030 MHz.
Level Control (ALC). The AM sig- the 8645A is designed to provide
The reference signal for this
nal is summed together with the sequences of many frequencies
phase lock loop originates from
level DAC which sets the ampli- in rapid order. Frequency
either an internal 10 MHz oscil-
tude level that reaches the atten- switching is specified as fast as
lator or an external input. An
uators. The combination of the 15 usec between frequencies. To
extensive divider section at the
level DAC, the AM signal, and accomplish this switching speed,
output of the phase lock loop
the attenuators (up to 120 dB of the fractional N phase lock loop
provides coverage down to
attenuation) determine the actu- is opened and replaced by a
252 kHz and a doubler in the
al output level of the 8645A. The delay line frequency lock loop.
output section extends the fre-
Reverse Power Protection (RPP) Phase noise and spurious signals
quency range to 2060 MHz. All
prevents the output circuits from on the VCO output are again
four modulation types are imple-
damaging signals externally decreased by the delay line and
mented in the 8645A with either
input through the generator's phase detector in the fast hop
the internal 400 kHz synthesizer
output. Controlling all of this enhancement section. VCO set-
integrated circuit providing the
hardware in the many states the tings learned before fast hop
modulation waveform or an
user can set up is a Motorola operation begins are sent to the
external input. Frequency modu-
68000 microprocessor. VCO through a pretune DAC in
lation uses two techniques
the order of the output frequen-
including an analog signal
The basic block diagram summa- cies the user wants and at the
summed into the VCO tuning
rized above produces all the tra- rate programmed. Amplitude
input and a digitized FM tech-
ditional functions of a signal information is simultaneously
nique that directly modifies the
generator. For the applications sent to the level DAC. A hard-
fractional N number of the phase
intended for the 8645A, the ware state machine programmed
lock loop. Phase modulation sig-
phase noise and spurious signals by the microprocessor provides
nals are summed directly into
must be very low at offsets all the fast control signals need-
the fractional N phase lock loop.
greater than approximately ed while fast hop operation is
Pulse modulation occurs directly
10 kHz. A major advantage of underway.
after the divider section.
the block diagram is that a
Amplitude modulation is accom-
clean-up loop based on a delay Many of the operational areas
line and a phase detector can be briefly discussed on this page
added in parallel to the fraction- are covered more thoroughly in
al N phase lock loop. The 70 nsec other parts of this product note.
delay line in the clean-up loop of Refer to the table of contents for
the phase noise enhancement a listing of the topics.
section decreases the phase
noise and spurious signals to
levels required by communica-
tions hardware tests.
3
4
Timebase
configurations
The frequency stability of the The output of this optional high To allow other instruments to
8645A depends a great deal on stability timebase is only routed use the timebase signal from the
the reference oscillator in use. to the rear panel of the instru- 8645A, the rear panel 10 MHz
The standard internal timebase ment as the oven ref output. An ref out output provides an out-
is a non-ovenized 10 MHz crystal external jumper cable is used to put of either the standard or
oscillator with a typical aging input this reference signal at the optional timebase that is cur-
rate of