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Dynamic Testing of Frequency
Agile Radios
BILL FLERCHINGER * TOM HIGGINS
RF & Microwave
Measurement
Symposium
and
Exhibition
Flin-
HEWLETT
~e. PACKARD
www.HPARCHIVE.com
Bill Flerchinger
Bill is a Regional Sales Engineer from t.he Spokane Division. lIe graduated from Washington State
University with a BSEE and is currently working on his Master from WSU.
Tom Higgins
Tom received his BSEE from Montana State University in 1985. As ault&D eugineer, Tom worked
on RF microcircuits for pulse generation in sigual generators, a rcfreuce loop and a floating am-
plifier in a uew function generator. He is currently working on his Masters from WSU.
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TESTING FREQUENCY AGILE RADIOS
With the technology in communications advancing every day, more complex communications systems
have emerged. These newer communications systems have been developed for several reasons. They
allow a means to more efficiently send information, to resist interference from the surrounding environ-
ments, to secure the information being sent from outside parties, to resist being jammed intentionally
from a third party, etc. One of the methods used by radio manufacturers that give a user additional
performance capability is to use spread spectrum techniques. Basically, the idea behind using spread
spectrum is to take the normal bandwidth of the information being sent and either spread it out (that is
to add additional signal to the transmitted information so that its effective bandwidth is increased consid-
erably) or to take the normal R.F. occupancy and spread it over a large number of frequencies (being
several octaves or even decades apart) or a combination of the two. In both cases, the information is
being transmitted in a much wider bandwidth than if no spreading was used. This increased bandwidth
makes the spread spectrum system more jam or interference resistant. It also helps avoid signal fading
common in fixed frequency systems due to multi-path signal cancellations. Military tactical radios are a
prime example of these techniques in use. The need for secure, jam resistant, reliable communications is
extremely important in field use. Radio manufacturers like ITT, Magnavox, Racal, Thompson, B.E.L.,
Harris, Marconi, etc., are or have developed radios that change frequency from a few times a second, to
thousands of times a second. While production of these radios has increased immensely in recent times,
very little, if any commercial test equipment has been developed for testing these radios. Manufacturers
have had to design custom test fixtures adapted from their own radio hardware that are expensive and
limited in capability. These test fixtures allowed manufacturers to develop and manufacture hopping
radios. However, now that there are larger productions lines and end users who want to evaluate the
performance of these radios, as they have in the past with conventional radios, the need for commercial
test equipment that will accurately dynamically test radios has arisen.
This paper addresses these issues and gives insight on how testing of frequency agile radios can be
performed using newly developed test instruments from Hewlett-Packard.
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Agenda
Review of Conventional Transceiver Testing
IFrequency Agile Transceiver Testing
Required IEquipment for IFrequency Agile Testing
Sychronization of the HIP 8645A
~nterfacing to the Rockwell/Collins 1M1P-83
Applications
Summary
MCG/Spokane Division rDlHEWLETT
rft ~PACKARD
Slide 2
A Frequency agile radio can
operate on a single channel
or over a number of channels
l11111
MCG/Spokane Division rDlHEWLETT
rf2 ~PACKARD
Slide 3
Nearly all frequency hopping radios currently being manufactured have a conventional single channel operation
mode built-in as well. One of the primary reasons that frequency agile radios have single channel capability is so
that they can communicate with older existing radios. This is very important to military organizations since they have
thousands of conventional tactical radios currently in use that need to be able to communicate with the newer radios.
Although at sometime in the future, the majority of tactical radios will probably have frequency agile capability,
upgrading of all these radios will take a considerable amount of time.
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Block Diagram of
Conventional Transceiver
MCG/Spokane Dlvlalon rI3 HEWLETT
rf3 ~PACKARD
Slide 4
This is a block diagram of a conventional radio lets quickly go through the various blocks of the receiver and trans-
mitter and discuss what the function of each is.
The RF signal arrives at the receiver, is filtered, amplified, and then down converted to an intermediate frequency. At
the I.F. level the signal is again filtered and amplified. The signal is then sent into a discriminator or envelope
detector (depending on whether the radio is a angle modulated or amplitude modulated) from which the audio is
then recovered.
On the other end a voice is input into a microphone and either amplitude modulates, or angle modulates the carrier,
and then is amplified. As you can see, there are several blocks that make up a transceiver. Although many of the
portions can be tested alone, (board level or modules) tests on the entire receiver or transmitter are desired. Tests
that enable the manufacturer to characterize the performance of his radio. Not only under normal operating condi-
tions but determining limits of the radio by simulating various field conditions. This not only tells how his radio will
operate in adverse conditions, but enables him to improve the radio design so that optimum performance can be
obtained from the design being used.
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TESTS DONE ON
CONVENTIONAL TRANSCEIVERS
RECEIVER TESTS IMPORTANCE
sensitivity Determines range of radio
Adjacent channel selectivity Determines radio's ability to reject signals In
adjacent channels
Spurious response attenuation Determines how well radio rejects unwanted
spurious signals
Audio tests Determines quality of recovered audio
TRANSMITTER TESTS
Frequency Error Determines accuracy of transmitted carrier
Carrier power Determines output power level
Adjacent channel power Determines power output in adjacent channels
Modulation limiting Determines modulation limiting capability
Audio tests Determines quality of transmitted audio
MeG/Spokane Dlvlaion rJ,~ HEWLETT
RF4 a!!~ PACKARD
Slide 5
Let's look at a few of the tests that evaluate the performance of these radios, who is interested in the performance,
and why.
There are basically three groups of people who are interested in having tests like these run on radios, 1) regulatory
commissions 2) users and 3) manufacturers
Regulatory commissions (FCC, EIA, CEPT, CCIRR, etc.) are performing these tests to determine if a manufacturer's
radio is operating within the standards they establish. With the RF spectrum being utilized nearer to its capacity,
stricter regulations are being placed on users. It is their job to see that all radios being sold are within these regulations.
Users are interested in doing these tests as it allows them to verify the specifications that a manufacturer guarantees
for a given radio. This also gives the user a standard by which he can evaluate the performance of radios built by
various manufacturers. Finally, it allows a user to quickly verify that his radios are fully operational or require repair
after they have been in use.
The manufacturers are interested in performing these tests as it helps them to precisely characterize their radios as
well as use the results to improve their radio design. In addition, it gives them a high confidence level that the radios
they are shipping will work. And, of course, the manufacturer's do these tests as the users and regulatory commis-
sions demand it.
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Block diagram of equipment for
performing conventional radio tests.
MCG/Spokane Division ~HEWLETT
rl5 EalPACKARD
Slide 6
Let's look at the block diagram of equipment that will allow us to perform all the tests that I previously listed as well
as many additional tests.
Note the methodology that is used for testing the transmitter and receiver. The idea here is to substitute calibrated
test equipment for all parts of the communication system except for, of course, the unit under test. By using cali-
brated test equipment the following advantages are gained:
1) The equipment has guaranteed specifications for its performance that are traceable to standards labs like NBS,
therefore allowing the user to very accurately measure and record specifications for his radio.
2) It allows operating parameters to be varied so that the results of these variations can be seen on the unit under test.
3) Eliminates discrepancy in the results obtained by two aifferent labs performing the same tests.
4) It provides a standard to be measured against when more than one source manufacturers the same radio.
5) It insures that the performance measured is that of the unit under test and not due to the uncertainty of
non-specified or uncalibrated test equipment.
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HP 8955A Transceiver Test System
III .....l;:1 .~~