Text preview for : 5952-1416.pdf part of HP 5952-1416 HP Publikacje 5952-1416.pdf
Back to : 5952-1416.pdf | Home
Agilent PN 8780A-2
Modulation Solutions for RF and Microwave
Receiver Test
Product Note
The Agilent 8780A--Off-the-Shelf
"Real World" Modulation
Today's advanced telemetry, terrestrial
and satellite communications receivers
vastly exceed the modulation capabil-
ities of traditional narrow-band analog
modulation signal generators. Testing
these advanced receivers often requires
custom-built test systems which include
complicated combinations of splitters,
filters and hybrid components.
The Agilent Technologies 8780A
Vector Signal Generator is Agilent's
answer to the custom-built modulator
for receiver test. It combines several
highly-advanced modulators in a sin-
gle programmable test instrument.
Capable of AM, FM, Phase Modulation,
and I/Q and Digital Modulations, the
8780A not only replaces most custom-
built modulators over the 10 MHz to
3 GHz IF frequency range, but improves
performance as well. And, unlike
custom-built solutions, the vector
signal generator has all the conven-
iences of a state-of-the-art synthesizer:
programmable level and frequency
plus automatic calibration at the
touch of a button.
This note describes the modulation
capabilities of the 8780A in detail. It
also includes several actual measure-
ments made on an 8780A sampled at
random to show how actual perform-
ance compares with the specifica-
tions. In most cases, there is consid-
erable margin in the specifications.
Hopefully, by presenting actual meas- Figure 1. Simplified 8780A Vector Signal Generator block diagram showing modulators
ured data, you will be able to better and frequency mixing
determine if the 8780A is suitable for
your applications. If you have to have
a tighter specification, please contact
your Field Engineer for a quote of a
special option.
New! Phase Modulation >10 MHz Frequency Modulation >12 MHz One of the most demanding applica-
BW, <10% THD, >3 Radians P-P BW, >50 MHz P-P Deviation tions for an FM modulator is the gen-
The FM modulator of the vector sig- eration of video signals. The vector
Deviation signal generator's AC FM is designed
In response to the needs of telemetry nal generator also benefits from its
location in the 8780A's multiplier with this challenge in mind.
customers, we've added phase modu-
chain. Not only are very wide peak-to- Differential gain and phase are speci-
lation to the 8780 as special option
peak deviations and rates possible, fied at less than 2% and 1 degree
H02. Because the vector signal gener-
but distortion is also very low. respectively for 27.6 MHz peak-to-
ator's phase modulator is placed in
peak deviations.
the multiplied LO path, very low dis-
tortion and wide deviations and rates FM modulation is available as nar-
rowband DC FM or wideband AC FM. Another very demanding application
are possible. This capability is espe-
The narrowband mode has lower for an FM modulator is the genera-
cially valuable is in the simulation of
phase noise. Narrow band DC FM is tion of CHIRP radar signals. The
satellite or range telemetry signals.
specified for up to 10 kHz BW and CHIRP graphs demonstrate the
Not only does the 8780A generate
150 kHz peak-to-peak deviations. The dynamic performance of the vector
telemetry signals, but it also gener-
wideband AC FM is specified for up signal generator's FM modulator,
ates the digital modulations used to
to 12 MHz BW and 50 MHz peak-to- showing in a single signal very high
carry data on satellite communica-
peak deviations. A special function is peak-to-peak frequency deviation, lin-
tions systems, and likely to carry
also available to extend peak-to-peak earity, and input bandwidth.
tomorrow's telemetry information as
well. DC FM deviations to >200 MHz, but
rates remain limited to the 10 kHz
Figure 2 shows one phase modula- input bandwidth.
tor's frequency response. Although
the bandwidth is specified to 10 MHz, Where extremely wide deviations and
this specification, like many on the input bandwidths are required, the
8780A, is conservative. As the graph 8780A FM modulator may be driven
shows, the measured response is flat directly by rerouting two internal
to within tenths of a dB to 10 MHz connectorized cables (remove cable
and isn't down 3 dB until more than from A7J6 and reconnect at A6J10).
80 MHz. In this configuration, the input band- Figure 3. Phase modulator distortion
width is >12 MHz and peak-to-peak
Phase modulation distortion is also deviations of >250 MHz are possible;
conservatively specified at 10%. however, this is basically an open
Figure 3 shows measured distortion loop VCO input and performance is
less than 1% for rates to 10 MHz and much less stable than other operating
peak-to-peak deviations less than the modes.
specified maximum 1.5 radians. Even
if the modulator is over-driven by a
factor of two, total harmonic distortion
remains well below the 10% specifica-
tion. Only at higher rates (eg. 20 MHz) Figure 4. Maximum FM deviation possible
does the distortion approach the without exceeding 8780A internal IF filter
specification, and then only when BWs
driven at very large deviations.
Figure 2. Phase modulator frequency
response
2
Vector Modulation >350 MHz BW Other direct benefits of using a fixed Digital Modulation
<1% Error frequency microwave I/Q modulator Most digital modulations can be
Many modern transmitters and are in bandwidth, flatness, and group easily generated using Agilent 8780A
receivers use vector or "I/Q" delay. Since the modulator operates Vector Signal Generator digital inputs
Modulation to encode digital signals at 8 GHz, the modulation frequencies directly. The generator supports BPSK,
or to completely analyze received sig- common in communications and QPSK, 8PSK, 16QAM, and 64QAM
nals in terms of phase and magni- radar systems (10 to 100 MHz) cover (with Option 64) with symbol rates
tude. The vector signal generator is very small fractional bandwidths. The up to 150 MHz covering most satellite
ready to test these receivers too. By result is extremely clean generation and terrestrial communications
operating at a fixed frequency, the of relatively low bandwidth signals applications.
generator's I/Q modulator provides (see phase modulation section) and
very accurate modulation with almost very wide bandwidth capability for Digital modulation accuracy of the
no quadrature error and amplitude I/Q modulation. The I and Q inputs generator is specified in maximum
imbalance. The heterodyne output on the 8780A are specified for band- percent error as a percent of full
section downconverts the signal to widths in excess of 350 MHz, but as scale output (the magnitude of the
the generator's 10 MHz to 3 GHz out- the measurement of one 8780A below largest signal state). I/Q errors are
put. The result is calibrated I/Q mod- shows, the actual 3 dB bandwidth is specified to be less than 1% for BPSK
ulation over more than 8 octaves of often in excess of 500 MHz. This is and QPSK, less than 1.2% for 8PSK
range--something impossible using particularly important where the I/Q and less than 2% for 16QAM. In fact,
custom-built modulators which inputs may be used to generate very measured error data is usually much
employ direct modulation techniques. high rate digital modulations (eg. better, as the sample of 16QAM con-
QPSK) for testing advanced satellite stellation errors plotted below shows.
communications modems. Maximum error for any of the 16
states was 0.5%--much lower than the
2% specification.
Figure 8. I/Q error versus I and Q drive voltages for all possible input values--no meas-
ured errors exceed 0.26%
Figure 5, 6, 7. Very wide deviation CHIRP Figure 9. Vector modulation frequency Figure 10. Digital modulation errors for all
pulse performance illustrates exceptional response digital states in an 8780A--none measured
FM performance exceed 0.5%
3
Putting it All Together When your own baseband signals are Agilent Technologies' Test and Measurement
inconvenient, or you want to eliminate Support, Services, and Assistance
The 8780A Vector Signal Generator's
Agilent Technologies aims to maximize
modulations are individually unsur- potential baseband errors which might
the value you receive, while minimizing
passed, and together provide unique degrade the generated modulation, your risk and problems. We strive to
solutions for receiver test. All of the Agilent has a wide range of function ensure that you get the test and measure-
generator's modulations are available and waveform generators which can ment capabilities you paid for and obtain
generate calibrated baseband signals. the support you need. Our extensive sup-
simultaneously except digital and vec- port resources and services can help you
tor modulations which work simulta- An especially important product to choose the right Agilent products for your
neously with all other modulations mention is the 8770A Arbitrary applications and apply them successfully.
except each other. The ability to simu- Waveform Synthesizer (AWS). The Every instrument and system we sell has
AWS generates arbitrary signals with a global warranty. Support is available
late multiple modulations simultane-
for at least five years beyond the produc-
ously adds to the generator's versatil- up to 50 MHz bandwidth ideal for
tion life of the product. Two concepts
ity, by allowing receiver margin test- driving any of the vector signal gener- underlie Agilent's overall support policy:
ing and accommodating receivers ator's analog inputs. "Our Promise" and "Your Advantage."
designed to work with multiple simul- Our Promise
taneous modulations. Ordering Information "Our Promise" means your Agilent test
and measurement equipment will meet its
8780A Vector Signal Generator advertised performance and functionality.
Modulation Sources Opt. 064 adds 64QAM When you are choosing new equipment,
With all of its bandwidth, you may be Opt. H02 adds phase modulation we will help you with product informa-
wondering where you get signals to Opt. 001 adds +10 dBm coherent tion, including realistic performance spec-
carrier (normally -20 dBm) ifications and practical recommendations
drive a modulator like the 8780A. One from experienced test engineers. When
excellent place is your own baseband Opt. H05 adds 8 GHz CW output you use Agilent equipment, we can verify
circuits. Proprietary filtering, shaping, (typically 0 to -4 dBm) that it works properly, help with product
and coding are often done at base- operation, and provide basic measurement
8770A Arbitrary Waveform assistance for the use of specified capabil-
band. By using your own baseband ities, at no extra cost upon request. Many
signals, you can be sure the signal Synthesizer self-help tools are available.
generated by the 8780A will be
Your Advantage
"understood" by your receiver. "Your Advantage" means that Agilent
offers a wide range of additional expert
test and measurement services, which you
can purchase according to your unique
technical and business needs. Solve prob-
lems efficiently and gain a competitive edge
by contracting with us for calibration, extra-
cost upgrades, out-of-warranty repairs, and
on-site education and training, as well
as design, system integration, project man-
agement, and other professional services.
Experienced Agilent engineers and techni-
cians worldwide can help you maximize
your productivity, optimize the return on
investment of your Agilent instruments and
systems, and obtain dependable measure-
ment accuracy for the life of those products.
Get assistance with all your
test and measurement needs at:
www.agilent.com/find/assist
Product specifications and descriptions in this
document subject to change without notice.
Copyright