Orban RET-041 Owner's manual

Installation and Operation Instructions
RETROFIT KIT RET-041
For OPTIMOD-AM Model 9100A/1 ( ono)
Purpose: Adds NRSC Pre-e phasis and 10kHz Low-pass Filter
(Retrofit Kit RET-033 must first be installed in units
with serial numbers below 700000.)
This kit modifies the Model 9100 /1 OPTIMOD- M® to provide the pre-emphasis and
1 0kHz low-pass filtering that is recommended by the National Radio Systems Commit 
tee (NRSC). 12kHz and 5kHz low-pass filtering are provided for stations that require
them. The filters can be preset, or can be switched by OPTIMOD- M ’ s day/night logic.
This kit also provides a means of de-emphasizing the NRSC pre-emphasized signal for
monitoring.
Retrofit Kit RET-041 contains:
1 Card#1F10
1 BLUE NRSC Pre-emphasis Module
2 30-gauge wires
1 Label, “ Special Modification"
1 Resistor, 100Q ±5%, 1 / 4 -watt, carbon film
2 Resistors, 620Q ±5%, 1 / 4 -watt, carbon film
1 Capacitor, 0.1 8pF ±5%, 1 0O-volt, metallized polyester
1 NRSC Compliance Card
1 Installation and Operation Instructions
These instructions first discuss the reasons behind the NRSC recommendations (starting
on the following page), then explain how to install the retrofit (on page 3).
Installation consists of positioning jumpers, setting controls, plugging a pre-emphasis
module into a socket, and inserting a new circuit card into a rack slot. simple de 
emphasis circuit can be installed for off-air monitoring.
In older units (with serial numbers below 700000), two jumpers must be attached to
the motherboard and a socket and interconnections for pre-emphasis modules must be
installed. (The socket and interconnections are supplied as RET-033, to be ordered
separately.)
Installation of this retrofit kit affects certain parts of the 91 00A Operating Manual, so a list
of changes to the manual is included (on page 9). lso included are field alignment
and performance verification instructions (on page 11), a circuit description (on
page 18), a parts list (on page 23), and schematics and assembly drawings (on page
26) for Card #1F10.
95307-000-01 6/87
Orban Associates Inc. 45 Bryant Street San Francisco, CA 94107
Main: (415) 957-10 3 Sales: (415) 957-10 7 Telex: 17-1480

page 2
RET-041 Instructions
95307-000-01 6/87
Why the New NRSC Standard?
Over the years, as the air waves became more crowded, interference from first and second
adjacent stations became more and more of a problem. Receiver manufacturers responded by
producing receivers with decreased audio bandwidth, so that the encroachment of an adjacent
station ’ s modulation extremes would not be audible as interference. This truncating of the
bandwidth had the effect of diminishing the receiver ’ s high-frequency response, but it was
felt that lower fidelity would be less obnoxious than interference. s long ago as 1978,
Orban proposed and implemented pre-emphasis and low-pass filtering for M broadcast to
provide brighter sound at the receiver while minimizing interference. This approach has
become widely accepted. Now the NRSC has formalized a standard which is acceptable to
all industry segments, and which can, if promptly implemented, result in a vast improvement
in M radio.
AM Stereo Introduces a Pre-e phasis Dile a
Certain M receivers manufactured since 1984, particularly those designed for domestic M
stereo reception, have a frequency response which is substantially wider than that of the
typical mono M receiver. The frequency response was widened largely to enhance the
sales potential of M stereo by presenting a dramatic, audible improvement in fidelity in
the showroom. s these new receivers became more prevalent, broadcasters had to choose
whether the station ’ s pre-emphasis would be optimized for the new M stereo receivers
or for the existing conventional receivers that form the vast majority of the market. If the
choice was for conventional receivers (which implies a relatively extreme pre-emphasis), the
newer receivers might sound strident or exceptionally bright If the choice favored the newer
receivers (less pre-emphasis and probably less processing), the majority of receivers would
be deprived of much high-end energy and would sound both quieter and duller.
NRSC Standard Pre-e phasis and Low-pass Filtering
In response to this dilemma, the National Radio Systems Committee (NRSC) undertook the
difficult task of defining a voluntary recommended pre-emphasis curve for M radio that
would be acceptable to broadcasters (who want the highest quality sound on the majority
of their listeners ’ radios) and to receiver manufacturers (who are primarily concerned with
interference from first- and second-adjacent stations).
fter a year of deliberation, a “ modified 75-microsecond ” pre-emphasis/de-emphasis standard
was approved. This provides a moderate amount of improvement for existing narrowband
radios, while optimizing the sound of wideband radios. Most importantly, it generates sub 
stantially less first-adjacent interference than do steeper pre-emphasis curves.
The second part of the NRSC standard calls for a sharp upper limit of 10kHz for the audio
presented to the transmitter. This essentially eliminates interference to second and higher
adjacencies. While some have protested that this is inadequate and that 15kHz audio should be
permitted, the unfortunate fact is that interference-free 15kHz audio could only be achieved by
a complete re-allocation of the M band! The practical effect of widespread implementation
of the 10kHz standard is that 10kHz radios will then be feasible, and the bandwidth perceived

95307-000-01 6/87 RET-041 Instructions
page 3
by the average consumer (now limited by the receiver to 3kHz, typically) will be dramatically
improved. On much mass-market equipment, it will be difficult to tell M from FM.
The radio manufacturers participating in the NRSC stated emphatically that reduction in
interference must be demonstrated by broadcasters before receiver manufacturers would be
willing to release true wideband (10kHz audio bandwidth) receivers to the mass market This
is rational — the receiver manufacturers can lose millions of dollars if they produce receivers
that are rejected as noisy or interference-prone by consumers. In contrast, broadcasters can
easily change pre-emphasis and filtering with very little expense.
Therefore, al±ough this standard is voluntary, we strongly recommend conformance to it.
We are convinced that use of this more modest pre-emphasis and sharp 10kHz filtering
by broadcasters is the only factor that will eventually induce the receiver manufacturers to
build and mass-market the high-fidelity, wideband radios which would allow M stations to
compete with FM in audio quality. The commitment to do so was strongly expressed by the
receiver manufacturers involved in the NRSC ’ s deliberations.
Installation
* llow about 30 minutes for this retrofit If installation of Retrofit Kit RET-033 will be
required (as it may for units with serial numbers below 700000), allow a total of up to F
hours.
1) Open the front panel of the 9100A/1, remove the subpanel.
It is not necessary to remove the unit from the rack (unless Retrofit Kit RET-033 must be
installed — see step 4). The 9100 /1 must, however, be off the air during this procedure.
a) Remove the three hex-socket screws at the top of the front panel with a %4-inch hex
wrench (provided with the unit), then tilt the hinged front panel downward to reveal
the interior.
b) Set the C POWER switch to OFF.
c) Loosen the four DZUS fasteners on the subpanel by turning each %-tum counterclock 
wise with a long 3 /i6-inch or * -inch flat-blade screwdriver.
d) Taking care not to stress the flat cables beneath it, tilt the top of the subpanel outward
and to the left to clear the upper chassis lip and the door support rail at the right
2) Reposition jumpers on Card #7.
a) Remove Card #7 from its slot.
b) Place jumper on Card #7 in the “ C RD 1 INST LLED ” position (see Fig. 1).
c) Return Card #7 to its slot.

page 4 RET-041 Instructions
95307-000-01 6/87
(as shipped)
ACCESSORY PORT
INSTALLED
SEPARATION TRIMMER
Fig. 1: Jumper Positions, Card #7
Fig. 2: Jumper Positions and Component Locations, Card #4

95307-000-01 6/87 RET-041 Instructions
page 5
3) Install NRSC pre-emphasis module on Card #4.
a) Remove Card #4 from its slot.
b) If the serial number of your 9100 /1 is below 700000, install Retrofit Kit RET-033
on Card #4 before continuing (instructions are provided with that kit).
c) Unplug the “ equalization module ” from the socket on Card #4.
Do not remove the module if it is BLUE. See Fig. 2 for location of the module. (On
some earlier versions of Card #4, the socket is on a “ transition board ” assembly.)
d) Insert the BLUE NRSC pre-emphasis module in the socket.
e) Check that jumper on Card #4 is in the “ MONO ” position.
f) Return Card #4 to its slot.
) If your serial number is below 700000, attach jumpers to motherboard.
\[Skip this step if your serial number is 700000 or higher.]
a) \Plug an extender board into slot #1.
b) Turn the POS peak THRESH control fully counterclockwise.
c) Set the MODE switch to OPER TE.
d) Set the C power switch to ON.
e) Measure the voltage between the chassis and pin U and between the chassis and pin
V. If these voltages are about -4.1 VDC and +4.1VDC, respectively, the jumpers are
already in place and you may skip to step 5.
\
f) Set the C POWER switch to OFF.
\
g) Disconnect OPTIMOD- M and remove it from the rack.
h) Remove the eight screws that attach the top cover to the rear panel of OPTIMOD- M.
lso remove the eight screws that attach the bottom cover to the rear paneL
\
i) Set the unit on a padded surface with the rear panel facing you and the bottom cover
down. \
Leave about 6 inches (15cm) between the rear panel and the edge of the table.
Be sure the C power cord is unplugged.
j) Remove the three groups of three screws circled in black on the rear panel.
k) Very carefully pull the rear panel about %-inch toward you, and then tilt the top of the
rear panel down until the rear panel is horizontal.
Careful! Watch for snags in the wiring or stress on the ceramic capacitors on the
internal divider wall or RF box. These capacitors are very fragile and are difficult
to replace. \

page 6
RET-041 Instructions
95307-000-01 6/87
Fig. 3: Motherboard Modification
(Only for units with serial numbers below 700000)
p) Replace the 25 screws removed above.
Do not tighten screws until all screws are loosely in place.
q) Return OPTIMOD- M to rack, connect and ground unit
1) On the motherboard, tack solder the supplied 30-gauge insulated hook-up wire from
pin 7-18 x to pin 1-U (see Fig. 3).
ard, tack solder the supplied 30-gauge insulated hook-up wire from
see Fig. 3). pin 7-V to pin 1-
n)
Check your work care y. Measure the voltage between the chassis and pin U and
between the chassis and pin V with the POS PE K THRESH control fully counterclockwise
(these voltages should be near -4.1VDC and +4.1VDC, respectively).
o) Very carefully tilt the rear panel up to the vertical position, and the push the rear panel
forward into place.
Take care that no wires are pinched between the panel and the chassis.
m) On the mothe

95307-000-01 6/87
RET-041 Instructions
page 7
5) Install Card #1F1O.
a) Remove Card #1 or #1-F from slot #1, if present.
b) Position jumpers (night) and B (day) on Card #1F1O to select the desired low-pass
filter (see Fig. 4).
You may select 5kHz, 10kHz, or 12kHz low-pass filtering in any combination for
day and night operation. The NRSC standard specifies 10kHz low-pass filtering
for both day and night
c) Insert Card #1F1O into slot #1.
#1F10
O o — • 5kHz — » QQ
[ooh — 10kHz — - fool NRSC (as shipped)
O O - — 12kHz — * o o
JUMPER-B
D Y
JUMPER
NIGHT
Fig. 4: Low-pass Filter Jumper Positions, Card #1 F1 0
) Reinstall subpanel and close the front panel.
The subpanel should al ays be replaced, since it is an integral part of the chassis RFI
protection.
a) Taking care not to stress the flat cables beneath it, tilt the top of the subpanel inward
and to the left to clear the upper chassis lip and the door support at the right
b) Turn the DZUS fasteners Mi-tum clockwise.
The DZUS fasteners turn only l / 4 -tum. Don ’ t force them, lest they be damaged
in a way that is very time consuming to repair.
c) Set the internal C POWER switch to ON.
d) Raise the front panel and fasten the three screws that secure it in place.

page 8 RET-041 Instructions
95307-000-01 6/87
7) Turn the HF EQ control fully clockwise.
This instruction supersedes the settings shown in Fig. 4-6 ( “ Recommended Initial Control
djustments ”) on page 4-7 of the Third Edition of the 9100 Operating Manual. You
may wish to note this change on that figure.
8) Attach the supplied “ Special Modification ” label to the rear panel.
9) Install NRSC de-emphasis circuit for monitoring.
The CC-5 Monitor Rolloff Filters supplied with 9100 /1 units were designed to comple 
ment the original GREEN module. When the BLUE module is used, a simple de-emphasis
circuit can be placed between the audio output of the modulation monitor and the input
of the monitor amplifier to provide complementary 75gs de-emphasis. For a more pre 
cise simulation of a “ standard ” NRSC receiver (including a 10kHz notch filter to reduce
any audible artifacts that might result from ringing introduced by the very sharp 10kHz
low-pass filter, and to eliminate 10kHz whistles encountered in off-air monitoring), we
recommend our CC-023 NRSC Monitor Rolloff Filter.
See Fig. 5 for a schematic of the simplified rolloff filter and information about installing
it (the parts needed are included in this kit). Note that the frequency response of this filter
is correct only when both its source and load impedances are approximately 600 ohms,
and that resistors or pads may have to added to achieve this.
Monitor Rolloff Filter
Monitor A p or D.A.
Modulation Monitor
Fig. 5: NRSC Simplified 75ps Monitor Rolloff Filter Schematic

95307-000-01 6/87
RET-041 Instructions
page 9
10) Complete and mail the supplied “ NRSC Compliance Card ” .
s explained in the introduction to this kit, making M audio quality competitive with
that of FM depends on M broadcasters demonstrating their commitment to the NRSC
standard. The N B is tallying M stations as they implement the standard, so that the
rate of implementation and the total number of equipped stations can be made known
to receiver manufacturers. Now that you have upgraded your equipment to the standard,
complete the job by returning the NRSC Compliance Card to the N B.
Operating Manual Changes
Installing this retrofit kit changes or invalidates portions of the 9100 Operating Manual.
The following changes to that manual update it to include this retrofit. To prevent future
errors, we recommend marking each page mentioned below with “ See Retrofit Kit RET-041
Instructions ” . (Page references are to the Third Edition of the 9100 Operating Manual;
“ ddendum #1 ” refers to ddendum #1 to that manual)
1) NRSC pre-emphasis is supplied by a BLUE module on Card #4 in the mono 9100 /1.
ddendum #1 provides information about these modules.
In the main body of the 9100 Operating Manual, the following pages are affected by
this change:
1- 4, 1-5 “ Introduction: High-Frequency Equalizer ”
3- 10 “ Installation: Option 7 ”
5-1, 5-2 “ Operating Instructions: Where to Start ”
5-4 “ Operating Instructions: HF EQ ”
5-7, 5-8 “ Operating Instructions: On High-Frequency Equalization ”
4- 7 During initial set-up, the 9100 /l ’ s HF EQ control should be turned fully
clockwise. This instruction supersedes the settings shown in Fig. 4-6.
6-1 “ Proof of Performance ” is unaffected by this change.
D-3 Program equalizer response will be as specified in ppendix D only
if the GREEN module is installed.
We continue to supply the older RED, YELLOW, and GREEN modules mentioned in the
9100 Operating Manual for stations (particularly those outside North merica) which
may prefer other HF equalization. See ddendum #1 for more information.
2) The CC-5 Monitor Rolloff Filter supplied with 9100 /1 units was designed to com 
plement the original GREEN module. The installation instructions above describe how to
apply a complementary de-emphasis for off-air monitoring of NRSC standard audio, and
explain when it might be preferable to use the optional CC-023 Monitor Rolloff Filter
instead. (See ddendum #1 for information about monitor rolloff filtering if you choose
to use one of the alternate pre-emphasis modules.)

page 10
RET — 041 Instructions
95307-000-01 6/87
This change affects the following pages in the 9100 Operating Manual:
2- 3 “ Various pplication Notes: Monitor Rolloff Filters ”
3- 10 “ Installation: Monitor Rolloff Filter ”
5- 3 “ Operating Instructions: Monitor Rolloff Filter ”
3) Low-pass filtering is selected by jumpers on Card #1F1O. Day and night 10kHz low-pass
filtering is specified in the NRSC standard. 5kHz and 12kHz low-pass filtering are also
available. ny of these three low-pass filtering options may be chosen for day operation,
and the same or either of the other two may be chosen for night operation.
These changes in low-pass filtering options affect the following pages:
1-1 “ Introduction and System Description ”
1-7, 1-8 “ Introduction: Output Low-pass Filter and Safety Clipper ”
2-5 “ Various pplication Notes: 5kHz Bandwidth Limitation ”
4) Card #1F1O replaces Card #1 or #1-F. Schematics and assembly drawings for Card #1F1O
are included in these instructions.
5) The specifications after installation of this retrofit are essentially the same as those given
in ppendix L of the 9100 Operating Manual. With the NRSC 10kHz low-pass filter in
the circuit, total system frequency response is better than +0.5dB, -2.0dB, 5O-96OOHz.
OPTIMOD is a registered trademark of Orban Associates Inc.

95307-000-01 6/87 RET-041 Instructions
page 11
Field Align ent and Perfor ance Verification
- Card #1 F10
Use the follo ing procedure to align and verify performance of Card #1F1O after the card has
been repaired.
This procedure is not required for routine maintenance or Proof of Performance.
Record all current control settings before beginning, so these settings can be restored
when this procedure is completed.
Record jumper positions when directed to reposition a jumper, so the jumpers can be
returned to these positions when you are finished.
Jumper and component locations are shown in the assembly drawings in the 9100 Op 
erating Manual and in installation instructions for retrofit kits containing Card #1F1O.
In a mono OPTIMOD- M, all connections are to the left input or output
lways turn off the power to OPTIMOD- M when removing circuit cards to move jumpers.
The alignment and verification procedure consists of:
- checking the accuracy of the DC reference voltage
- verifying the performance of the 5kHz and 10kHz low-pass filters
- checking DC servo operation
- adjusting the gain of the 10kHz low-pass filter
- adjusting the notch frequency of the 10kHz low-pass filter
- verifying distortion and noise performance
Follow instructions in the order given, without skipping steps.

page 12
RET-041 Instructions
95307-000-01 6/87
Equip ent required:
Low-frequency spectrum analyzer with tracking generator
Tektronix 5L4N plug-in with 5111 bistable storage mainframe, or equivalent. lter 
natively, a sweep generator with 20-20, 000Hz logarithmic sweep can be used (with
the oscilloscope in X/Y mode).
Oscilloscope
With DC-coupling, dual trace, triggered sweep, and 5MHz or greater vertical band 
width. x 10 probe.
udio oscillator
Residual distortion less than 0.0015%.
Frequency counter
ccurate to ±0.05%
Total harmonic distortion (THD) analyzer
Residual distortion less than 0.0015%.
udio voltmeter
ccurate to ±2%. (Sound Technology 1700 /B or 1710, for example.)
Pink noise generator
Digital voltmeter
ccurate to ±0.1%.
It is assumed that the technician is thoroughly familiar ith the operation of this equip 
ment.
1) Open the front panel of the OPTIMOD-AM, remove the subpanel.
It is not necessary to remove the unit from the rack, as long as you have access to the input
terminals on the rear panel. The OPTIMOD- M must, however, be off the air during this
procedure.
a) Remove the three hex-socket screws at the top of the front panel with a %4-inch hex
wrench (provided with the unit), then tilt the hinged front panel downward to reveal
the interior.
b) Loosen the four DZUS fasteners on the subpanel by turning each V 4 -tum counterclock 
wise with a long 3 /i6-inch or y 4 -inch flat-blade screwdriver.
c) Taking care not to stress the flat cables beneath it, tilt the top of the subpanel outward
and to the left to clear the upper chassis lip and the door support rail at the right.

95307-000-01 6/87
RET-041 Instructions
page 13
2) Extend Card #1F1O.
Remove Card #1F1O, insert a card extender into slot #1 of OPTIMOD- M ’ s card cage,
and then plug Card #1F1O into the extender card.
3) Verify DC voltages.
Measure voltages against circuit ground (available at pin C of the edge connector on Card
#1F1O.).
a) Set the MODE switch to OPER TE.
b) Turn the POS PE K THRESH control fully counterclockwise.
c) Measure the voltage at the anode of diode CR2 on Card #1F1O to verify that it is -4.1
volts DC, ±0.4V.
d) Measure the voltage at the cathode of diode CR1 on Card #1F1O to verify that it is
+4.1 volts DC, ±0.4V.
e) Set the MODE switch to PROOF.
f) Measure the voltage at the anode of diode CR2 on Card #1F1O to verify that it is
approximately -14 volts DC.
g) Measure the voltage at the cathode of diode CR1 on Card #1F1O to verify that it is
approximately +14 volts DC.
4) Verify performance of the 5kHz low-pass filter, and of “ bypass ” .
In “ bypass ” , 12kHz low-pass filtering is provided by other OPTIMOD- M cards.
a) Connect the output of a sweep or tracking generator to OPTIMOD- M ’ s input
b) Connect the input of a spectrum analyzer or oscilloscope to TP2 on Card #1F1O.
c) Place jumpers (night) and B (day) on Card #1F1O in the “ 12kHz ” position.
d) Verify that response is flat ± IdB to 12kHz.
e) Place jumpers (night) and B (day) on Card #1F1O in the “ 5kHz ” position.
f) Verify that response is flat ± IdB to 5.0kHz, and rolls off with a slope of greater than
30dB/octave above 5kHz.
It is normal to see a slight “ glitch** at 10kHz about -30dB.
g) Place jumper B (day) on Card #1F1O in the “ 12kHz ” position.
h) Verify that the 5kHz low-pass filter is activated when the TX EQ D Y/NIGHT switch is
moved to the NIGHT position.
If the filter is operating, you will see a steep rolloff of frequencies higher than
5kHz, as above.

page 14
RET-041 Instructions
95307-000-01 6/87
i) Verify that the 5kHz low-pass filter is deactivated when the TX EQ day / night switch
is moved to the D Y position.
If the filter is inactive, you will not see a steep rolloff above 5kHz.
j) On Card #1F1O, place jumper (night) in the “ 12kHz ” position, and jumper B (day)
in the “ 5kHz ” position.
k) Verify that the 5kHz low-pass filter is activated when the TX EQ day / night switch is
moved to the D Y position.
1) Verify that the 5kHz low-pass filter is deactivated when the TX EQ D Y/NIGHT switch
is moved to the NIGHT position.
m) Disconnect the sweep or tracking generator and spectrum analyzer or oscilloscope from
OPTIMOD- M.
5) Check DC servo operation.
a) Place jumper (night) and B (day) on Card #1F1O in the “ 10kHz ” position.
b) With a digital voltmeter, verify that the DC offset is less than 15mV at TP2.
) Adjust 10kHz low-pass filter gain.
a) On Card #1F1O, place jumper _B (day) in the “ 12kHz ” position.
b) Connect an audio oscillator to OPTIMOD- M ’ s input
c) Set OPTIMOD- M ’ s VU meter selector to L GC.
d) Set the audio oscillator to 1kHz, and adjust its output level until OPTIMOD- M*s VU
meter reads approximately “ -6VU ” .
e) Set OPTIMOD- M ’ s TX EQ D Y/NIGHT switch to D Y.
f) Observe the level at TP2. Make a note of it
g) Move the TX EQ D Y/NIGHT switch to the NIGHT position.
h) djust trimmer R62 until the level at TP2 is the same (±0.1dB) as that observed in
step f, above.
7) Adjust frequency of the first 10kHz low-pass filter ’ s notch.
a) Place jumper B (day) on Card #1F1O in the “ 10kHz ” position.
b) Set the audio oscillator for 10,100Hz ±10Hz, and check the frequency with a counter.
The audio oscillator should still be connected to OPTIMOD- M ’ s input Do not
change the audio oscillator ’ s output level.
c) While observing TP2 with an audio voltmeter, adjust trimmer R17 to null the signal.
The null should be more than 45dB below the input signal level.

95307-000-01 6/87
RET-041 Instructions
page 15
d) Disconnect the audio oscillator and voltmeter from OPTIMOD- M.
8) Verify 10kHz low-pass filter performance.
a) Connect the output of the sweep or tracking generator to OPTIMOD- M ’ s input.
b) Connect the input of the spectrum analyzer or oscilloscope to TP2.
c) Verify that response is flat +0.5dB, -2.0dB to 9600Hz, and rolls off with a slope of
greater than 60dB/octave above 10kHz.
d) Place jumper B (day) on Card #1F1O in the “ 12kHz ” position.
e) Verify that the 10kHz low-pass filter is activated when the TX EQ D Y/NIGHT switch is
moved to the NIGHT position.
If the filter is operating, you will see a very steep rolloff of frequencies higher
than 10kHz.
f) Verify that the 10kHz low-pass filter is deactivated when the Tk EQ D Y/NIGHT switch
is moved to the D Y position.
If the filter is inactive, you will not see a steep rolloff above 10kHz.
g) On Card #1F1O, place jumper (night) in the “ 12kHz ” position, and jumper B (day)
in the “ 10kHz ” position.
h) Verify that the 10kHz low-pass filter is activated when the TX EQ D Y/NIGHT switch is
moved to the D Y position.
i) Verify that the 10kHz low-pass filter is deactivated when the TX EQ D Y/NIGHT switch
is moved to the NIGHT position.
j) Disconnect the sweep or tracking generator and spectrum analyzer or oscilloscope from
OPTIMOD- M.
9) Verify distortion performance.
a) Place jumper B (day) on Card #1F1O in the “ 5kHz ” position.
b) Connect the input of a THD analyzer to TP2.
C) Set the TX EQ D Y/NIGHT switch to D Y.
d) Verify that distortion is less than 0.2% with the audio oscillator set for 100Hz, 1.0kHz,
and 4.0kHz in a 20-20, 000Hz bandwidth.
e) Set the TX EQ D Y/NIGHT switch to NIGHT.
f) Verify that distortion is less than 0.2% with the audio oscillator set for 100Hz, 1.0kHz,
5.0kHz, and 10.0kHz in a 20-20, 000Hz bandwidth.
g) Place jumper (night) on Card #1F1O in the “ 10kHz ” position.
h) Verify that distortion is less than 0.2% with the audio oscillator set for 100Hz, 1.0kHz,
5.0kHz, and 9.0kHz in a 20-20, 000Hz bandwidth.

page 16
RET-041 Instructions
95307-000-01 6/87
i) Disconnect the THD analyzer from TP2.
10) Verify noise performance.
a) Check that jumper (night) on Card #1F1O is in the “ 10kHz ” position.
b) Connect the audio voltmeter to TP2.
c) Short OPTIMOD- M ’ s input by connecting the L INPUT +, and GROUND terminals
together.
d) Set the TX EQ D Y/NIGHT switch to D Y.
e) Verify that the level of residual noise, as measured by the audio voltmeter, is less than
-65dBu from 20-20, 000Hz.
dBu = dBm at 600 ohms.
f) Set the TX EQ D Y/NIGHT Switch to NIGHT.
g) Verify that the level of residual noise, as measured by the audio voltmeter, is less than
-65dBu from 20-20, 000Hz.
h) Remove the jumper(s) shorting OPTIMOD- M ’ s input.
11) Restore all jumpers to the positions they were in at the beginning of this
alignment and performance verification procedure.
12) Remove the card extender and return Card #1F1O to slot #1.
13) Replace subpanel, close front panel.
The subpanel should al ays be replaced, since it is an integral part of the chassis RFI
protection.
a) Disconnect all test instruments from OPTIMOD- M.
b) Taking care not to stress the flat cables beneath it, tilt the top of the subpanel inward
and to the left to clear the upper chassis lip and the door support at the right
c) Turn the DZUS fasteners ’ -tum clockwise.
The DZUS fasteners turn only y 4 -tum. Don ’ t force them, lest they be damaged
in a way that is very time consuming to repair.
d) Set the internal C POWER switch to ON.
e) Raise the front panel and fasten the three screws that secure it in place.
14) Restore all controls to their settings prior to beginning this alignment and
performance verification procedure.

95307-000-01 6/87
RET-041 Instructions page 17
REPLACBS CARP* 1 IM MAIM BLOC OASeAM-
Fig. : Block Diagram, Card #1 F1 0

page 18
RET-041 Instructions
95307-000-01 6/87
Circuit Description — Card #1 F10
Card #1F1O is divided into two “ subsystems ” , which are described below in order of signal
flow. The block diagram in Fig. 6 illustrates this description.
1) 5kHz Low-Pass Filter
This is a unity-gain, phase-corrected, 5th-order Chebychev filter with O.ldB frequency re 
sponse irregularity and a -O.ldB bandwidth of 5.0kHz.
IC8a and associated components form a third-order non-inverting filter with a gently rolled-
off frequency response. The 5th-order filter ’ s frequency response shaping is completed by
IC9a and associated components, which form a 2nd-order inverting filter when the circuit
path is completed by strapping jumper B (D Y) or (NIGHT) to the “ 5kHz ” position.
IC8b and associated components form a phase corrector, which is an all-pass filter with
flat magnitude response and frequency-dependent phase response. This filter adds delay as
necessary to make the delay of the entire filter approximately constant with frequency, thereby
minimizing overshoot.
D Y/NIGHT switching is effected by very simple logic. Pin T on the card is low (-15V)
when OPTIMOD- M is in NIGHT mode, and high (ground) when it is in D Y mode. The
logic level at pin T drives JFET Q2 directly. QI inverts the logic and drives Q3. Q2 and Q3
are on when their gates are at ground, and off when their gates are at -15V. Thus Q3 turns
on in NIGHT mode and connects jumper into the circuit path, while Q2 turns on in D Y
mode, and connects jumper B into the circuit path.
2) 10kHz (NRSC) Low-Pass Filter
The signal can be routed to a 10kHz overshoot-compensated low-pass filter, consisting of a
first and second filter in series, with embedded clippers.
The signal enters the filter system and encounters clipper CR1, CR2, which provides main
peak control for the signal. fter buffering by ICla, the clipped signal is applied to the
first 10kHz filter IC2, IC3, IC4 (and associated components). This filter is very steep, and
removes the harmonics introduced by the clipping in CR1, CR2, as well as any significant
program energy above 10kHz.
The first filter is an active-RC analog of a passive LC ladder filter. It is realized by resistors,
capacitors, and frequency-dependent negative resistors (FDNRs). n FDNR is realized with a
dual opamp, three resistors, and two capacitors. When the passive LC filter is transformed into
an active RC filter, inductors become resistors, resistors become capacitors, and capacitors
become FDNRs.
Each FDNR resonates with a series resistor to create a notch in the frequency response of
the filter. (This is analogous to a series LC circuit to ground.) The notches are located in the
“ stopband ” (beyond approximately 10.05kHz). The circuit associated with IC2 produces a
notch at 10.65kHz ±4%. The circuit associated with IC3 produces a notch at 12.00kHz ±4%.
The circuit associated with IC4 is tuned by R39 to produce a notch at precisely 10.10kHz to

95307-000-01 6/87
RET-041 Instructions
page 19
ensure that the filter ’ s response falls accurately above 10kHz, and ±at NRSC specifications
are met
Measuring the frequency of these notches and their depth is the best way of diagnosing
problems with such filters, since problems with a given notch can be associated with a given
FDNR in most cases.
Because all parts of the filter interact, failures which cannot be cured merely by replac 
ing opamps are best left to factory service, since special tight-tolerance, tight-temperature-
coefficient parts are used in certain places. (The circuitry has been designed to be insensitive
to normal unit-to-unit variations in opamps.) See ppendix F in the 9100 Operating Man 
ual or Section 5 in the 9100B Operating Manual for information on how to obtain factory
service.
To avoid possible clipping, the signal is attenuated 5dB with voltage divider R24, R25 before
being applied to the filter. This gain is made up by IC5a to restore unity gain at low
frequencies.
ll-pass delay corrector IC5b adds frequency-dependent delay to the first filter as necessary
to make its time delay more constant with frequency, thereby minimizing overshoot
ny residual overshoot is then clipped in IC6a, and then the signal is applied to second
10kHz filter IC6b, IC7a. The primary purpose of this second filter is to remove harmonics
caused by clipping in IC6a.
Fig. 7: Response of the First 10kHz Low-Pass Filter in the Passband

page 20 RET-041 Instructions
95307-000-01 6/87
Fig. 8: Response of the First 10kHz Low-Pass Filter in the Passband and Stopband
Finally, all-pass delay corrector IC7b adds delay as necessary to make the delay of the second
filter more constant with frequency.
Fig. 9 shows the normal frequency response of the part of the second filter associated with
IC6b, while Fig. 10 shows the normal frequency response of the part of the second filter
associated with IC7a. Fig. 11 shows the overall frequency response of the second filter.
The normal frequency response of each all-pass delay corrector (IC5b and IC7b) is flat,
although each has a frequency-dependent phase shift IClOb and associated components act
as a servo to eliminate DC offset at the output of IC9b.
Fig. 12 shows the normal power spectrum measured at OPTIMOD- M ’ s output with the
10kHz filter strapped in and bright program material applied to OPTIMOD- M ’ s input The
measurement (made with an 801 -line FFT spectrum analyzer operated in “ peak hold ” mode
over a 20-minute observation period with OPTIMOD- M controls at the normal recom 
mended settings) verifies that NRSC power bandwidth specifications are met by the system.
The 10kHz filters can be strapped into the circuit with jumpers and B. These jumpers
can also be configured to bypass all filters on Card #1F1O, retaining only the built-in 12kHz
filtering provided elsewhere in OPTIMOD- M.