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Configuring the HP 4396B
for O/E Testing
Application Note 1288-2
Introduction The recent trend in cable television (CATV) is the need for more
selections, or channels, and the possibility of having interactive TV
services such as On-Line-Banking and Movies-on-Demand. These
requirements are pushing the limits of the copper cabling already laid out
for today's CATV systems and these systems are not able to provide the
"500 channels" of TV for the future. The industry is now changing from
copper cable to fiber optic cable to carry the signals to the consumer.
The fiber optic cable carries the channel information as light signals, but
all major TV equipment works upon electrical signals. Hence, tomorrow's
CATV systems needs both electrical-to-optical converters (E/O) and
optical-to-electrical (O/E) converters. An O/E converter changes light
signals to electrical signals, and an E/O converter does the reverse.
These converters need to be tested for conversion flatness and efficiency.
A converter with too much ripple can cause distortions in the TV channels
audio or video signals, which will show on the TV screen. A converter
with low efficiency, or gain, can lead to low signal-to-noise ratio, which
would cause "snow" on the TV. A converter without flat group delay will
affect the quality of the audio and color of the channel.
There is a myriad of tests performed on these converters; this paper will
concentrate solely on the test system setup for O/E converter test, using
the HP 4396B 1.8 GHz Combination Analyzer.
The HP 4396B The HP 4396B combines a network analyzer (NA), spectrum analyzer (SA),
and impedance analyzer (ZA) into a single instrument. This combination
allows for some major advantages:
1. Reduced capital equipment cost -- The HP 4396B costs less than a
comparable network analyzer and spectrum analyzer if they were
purchased separately.
2. Simplicity -- The HP 4396B is simpler to use. The front panel interface is
always the same for every mode of the combination analyzer. Knowing
how to operate the HP 4396B means you can operate 3 analyzers without
constantly connecting and reconnecting the cables.
3. Accuracy -- The HP 4396B uses the latest digital signal processing (DSP)
techniques to enhance its performance. The HP 4396B has digital
bandwidth filters and a stepped FFT technique for speed and accuracy.
4. Power -- The HP 4396B has several powerful functions to enhance your
testing capabilities, such as List Sweep, a built-in floppy disk drive (FDD),
and a controller capability with HP IBASIC to automate testing or test
systems.
HP IBASIC allows for convenient control of the HP 4396B and automates
testing. In this note, HP IBASIC is used to determine the offset factors for
the E/O converter. In order to test an O/E converter, an optical system or
an E/O converter must be characterized. These characteristics are placed
into the HP 4396B memory array and subtracted from the actual E/O-O/E
measurement to obtain the O/E parameters.
The HP 83400 series of Lightwave Sources are excellent E/O converters,
with modulation bandwidths from 300 kHz to 3 GHz. They come provided
with a disk of calibrated conversion parameters specific to each individual
unit.
With an IBASIC program, the HP 4396B can read the E/O instrument disk
and interpolate the conversion parameters for any bandwidth of interest.
The HP IBASIC program will then put into the HP 4396B memory array the
E/O conversion parameters. This HP IBASIC program is available from
your local HP field sales representative upon request. (See Appendix for
program listing.)
Conversely, the HP 83410 series of Optical Receivers can be used to
characterize an E/O system. Instead of using a calibrated E/O for the test
system, a calibrated O/E can be used to find the characteristics of the E/O
Page 2
system. This data can be factored into the measurements to obtain the
corrected O/E device characteristics.
&+ 6 ORJ G% 5()
(2 &RQ Y HU WHU
&RU
+ OG
([W 5HI
,) %:N0 ]
32:(5 6:3
67$57 0 + ]
6723
Figure 1. Conversion Flatness for the HP 83400B
The HP 4396B for testing One of the first tests of an O/E converter is magnitude and group delay
O/E Conversion Flatness flatness, also called conversion flatness. Conversion flatness indicates
whether the device converts signals from light to electricity in a manner
that is relatively flat over a given bandwidth. For TV signals, a channel
bandwidth is 6 MHz.
The system layout is given in Figure 2. The output from the network
analyzer source is split; half the signal is returned to the analyzer's
reference port, while the other half goes to the E/O converter. The optical
output from the E/O is connected via fiber optic cable to the O/E converter
(DUT). The electrical output of the O/E is the sent on to the Analyzer's
transmission port. An S-parameter test set can also be used to make full
2-port S parameter measurements, although E/O converter will remain the
same in every measurement.
+3$
HP 4396B
$ # #
3RZ HU 6SOL W W HU
(2&RQYHUWHU 2(&RQYHUWHU'87
)LEHU 2SW LF &DEO H
Figure 2. Network Analysis System Setup.
Page 3
After completing a THRU calibration by bypassing the E/O and O/E
converters, the system is ready to make measurements. The calibrated
data measured by the analyzer is the total conversion of both the E/O and
the O/E converters. To get just the O/E converter conversion data, the
analyzer will then subtract the conversion parameters of the E/O
converter. The resultant trace, DATA - MEMORY, is the conversion
flatness of the DUT. A sample Conversion Flatness result is given in
Figure 3.
The HP 4396B has a full vector network analyzer, which means it
processes phase information in its measurements. The phase information
combined with the frequency information results in group delay
information.
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Figure 3. Corrected O/E Converter Amplitude Flatness.
The HP 4396B The HP 4396B has a powerful spectrum analyzer inside. It has a dedicated
Spectrum Analyzer Spectrum Input Port, and can also monitor the spectrum from the R, A, or
B ports. A spectrum analyzer allows spectral testing of a component for
Carrier-to-Noise (C/N), Harmonics, Hum, and Composite Triple Beat
(CTB). A system schematic for CTB testing is shown in Figure 4. Separate
signal generators are necessary to drive the E/O converter.
+3$
HP 4396B
$ # #
6LJQDO*HQHUDW RU (2 &RQY HUWHU 2( &RQYHUWHU'87
)L EHU 2SW L F &D EOH
6LJQDO*HQHUDW RU
3RZ HU&RPELQHU
Figure 4. Spectrum Analysis IMD Test Setup
Page 4
In Figure 4, only one E/O converter is used with the two signal generators
combined at the input to the E/O. Depending on the specifications of the
E/O, two E/O converters can be used: one attached to the output of each
signal generator, with an optical combiner to combine them before the
input to the O/E under test. A screen from a CTB test is shown in figure 5.
G%5 ()
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&RU
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5 %: N+ ] 9%:N+ ] $7 1 G% 6:3
&(1 7 (5 0 + ] 63$1
Figure 5. Spectrum Analyzer CTB Test Results
C/N measures the amount of signal present compared to the amount of
noise on the signal. Too little C/N means "snow" on the TV screen. CTB
measures the amount of distortion from in-channel signals that "leaks" to
other channels. This is called crossmodulation or crossmod, and typically
is represented by jittery diagonal lines on the TV. Hum measures the AM
modulation of the signal carrier due to the electrical power system. The
TV picture will show overlaid horizontal if too much hum is present.
Conclusion The HP 4396B fits in perfectly for testing CATV components, electrically
and optically. The use of the calibrated Optical Transmitters and
Receivers allows for manufacturing test of O/E converters. The HP 4396B
has a third analyzer in it, an impedance analyzer for measuring passive
components. This triple functionality of the HP 4396B also makes it a very
useful tool for R&D engineers making CATV components.
Page 5
Appendix 10410 IF Points<>Pnts OR Sta<>Strt OR Sto<>Stp
THEN
Program Listing 10420 GOSUB Correction
10430 END IF
10000 ! Program to be run by HP4396B internal 10440 END LOOP
IBASIC 10450 STOP
10010 ! This program uses the correction factors for 10460 !
10020 ! an HP83411C lightwave receiver as found 10470 Correction:!
on 10480 BEEP
10030 ! the floppy disc shiped with the HP83411C 10490 !
for 10500 ! Save new Points, Sta and Sto values
10040 ! use with an HP8702. 10510 !
10050 ! The name of the file to be used must be 10520 Pnts=Points
10060 ! entered below. 10530 Strt=Sta
10070 ! At startup and whenever the start frequency, 10540 Stp=Sto
10080 ! the stop frequency or the number of points is 10550 !
10090 ! changed this program will re-calculate the 10560 OUTPUT @Hp4396;";MEAS S21" ! Meas
10100 ! correction data for the HP83411C and store S21
10110 ! this data in the so called memory array of 10570 OUTPUT @Hp4396;";HOLD" ! Stop
10120 ! the HP4396B after which DATA+MEMORY sweep
is 10580 OUTPUT @Hp4396;";DISA ALLB" ! Claim
10130 ! selected for display. This way all displayed display
10140 ! data is corrected for the HP83411C. 10590 !
10150 REM 10600 PRINT
10151 COM /Ampl_phase/ 10610 PRINT
Ampl(1:101,1:2),Phase(1:101,1:2),Delay 10620 !
10160 INTEGER One_point,Err,Error 10630 GOSUB Err
10170 REAL Points,Pnts 10640 !
10180 REAL Strt,Stp,Sta,Sto 10650 IF Error=0 THEN
10190 REAL Dat(1:801,1:2) 10660 !
10200 DIM Err$[256],Error$[256],Filename$[256] 10670 ! Get correction values from disc.
10210 ! 10680 !
10220 10690 Read_floppy(Filename$,Error,Error$)
!=============================== 10700 END IF
======== 10710 !
10230 Filename$="" ! Enter filename here 10720 IF Error=0 THEN
10240 10730 PRINT
!=============================== 10740 PRINT
======== 10750 PRINT
10250 ! 10760 PRINT "RE-CALCULATING HP83411C
10251 Delay=0 CORRECTION CURVE"
10252 ! 10770 PRINT
10260 RAD 10780 PRINT USING "K,10D";"Start frequency
10270 ! :";Sta
10280 ASSIGN @Hp4396 TO 800 10790 PRINT USING "K,10D";"Stop frequency
10290 ASSIGN @Bin TO 8;FORMAT OFF :";Sto
10300 ! 10800 PRINT "Number of points :";Points
10310 ON KEY 1 LABEL "RETRY CAL" GOSUB 10810 !
Calkey 10820 ! Calculate new correction by interpolation
10320 ! 10830 !
10330 LOOP 10840 Mkd(Strt,Stp,Pnts,Dat(*))
10340 OUTPUT @Hp4396;";POIN?" ! # of 10850 !
datapoints 10860 ! Send data header information
10350 ENTER @Hp4396;Points 10870 !
10360 OUTPUT @Hp4396;"STAR?" ! Start 10880 OUTPUT @Hp4396 USING
frequency "#,K";";FORM3;INPUDATA "
10370 ENTER @Hp4396;Sta 10890 OUTPUT @Hp4396 USING
10380 OUTPUT @Hp4396;"STOP?" ! Stop "#,K,6Z";"#6",Points*16
frequency 10900 !
10390 ENTER @Hp4396;Sto 10910 ! Send data and manipulate.
10400 ! 10920 !
10930 GOSUB Send ! To DATA arrays
Page 6
10940 OUTPUT @Hp4396;";DATMEM" ! To
MEMORY arrays
10950 OUTPUT @Hp4396;";SAVC" !
Re-calculate CAL
10960 OUTPUT @Hp4396;";MATH DPLM" ! Disp
DataPLusMem
10970 END IF
10980 !
10990 IF Error THEN
11000 Error=0
11010 OUTPUT @Hp4396;";DISA HIHB"! Claim
50% display
11020 !
11030 PRINT Error$
11040 PRINT
11050 PRINT "Correction failed. Check :"
11060 PRINT
11070 PRINT "- START frequency"
11080 PRINT "- STOP frequency"
11090 PRINT "- NUMBER of POINTS"
11100 PRINT
11110 PRINT "and change to correct values."
11120 PRINT "OR press RETRY CAL to retry with
current values."
11130 !
11140 OUTPUT @Hp4396;";KEY 47" ! System
menu
11150 OUTPUT @Hp4396;";KEY 0" ! IBASIC
11160 OUTPUT @Hp4396;";KEY 6" ! ON KEY
LABELS
11170 ELSE
11180 OUTPUT @Hp4396;";DISA ALLI" ! Release
display
11190 END IF
11200 !
11210 OUTPUT @Hp4396;";CONT"
11220 RETURN
11230 !
11240 Send: !
11250 FOR One_point=1 TO Points-1
11260 OUTPUT
@Bin;Dat(One_point,1),Dat(One_point,2)
11270 NEXT One_point
11280 OUTPUT
@Bin;Dat(One_point,1),Dat(One_point,2)
END
11290 GOSUB Err
11300 RETURN
11310 !
11320 Calkey: !
Page 7
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Test and Measurement products,
applications, services, and for a current sales
office listing, visit our web site,
http://www.hp.com/go/tmdir. You can also
contact one of the following centers and ask
for a test and measurement sales
representative.
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