Orban RET-044 Owner's manual

orbon*
Installation and Operation Instructions
RETROFIT KIT RET-044
For OPTIMOD-AM Models 9000A and 9000A/1
Purpose: Adds NRSC Pre-emphasis and 10kHz Low-pass Filter
This kit modifies the Model 9000A or 9000A/1 OPTIMOD-AM® to provide the pre-
emphasis and 10kHz low-pass filtering that is required by the National Radio Systems
Committee (NRSC). 11kHz and 5kHz low-pass filtering are provided for stations that re-
quire them. The filters can be preset, or can be switched by OPTIMOD-AM’s day/night
logic. This kit also provides ameans of de-emphasizing the NRSC pre-emphasized
signal for monitoring.
Retrofit Kit RET-044 contains;
1
1
2
1
1
1
1
1
1
1
1
1
2
1
1
1
2
1
1
Capacitor, 1300pF ±2%, mica
Resistor, 5.49K ±1%, Vs-watt, metal film
Resistors, 8.66K ±1%, Va-watt metal film
Resistor, 3.1 6K ±1%, Va-watt metal film
Resistor, 49.9K ±1%, Va-watt metal film
Resistor, 1.27meg ±1%, Va-watt metal film
(green-yellow-white-brown-brown)
(gray-blue-blue-brown-brown)
(orange-brown-blue-brown-brown)
(yellow-white-white-red-brown)
(brown-red-violet-yellow-brown)
Resistor, 10.0K±1%, Va-watt metal film (brown-black-black-red-brown)
Opamp (TL072) 1C
Capacitor, 0.1 |xF ±10% metallized polyester
28-gauge jumper wire
Resistor, 75.0K±1%, Va-watt metal film (violet-green-black-red-brown)
Pre-wired 22-pin card connector with mounting hardware
Card guides
#1 F10 Card
Label, “Special Modification"
Resistor, lOOn ±5%, 'A-watt, carbon film
Resistors, 620J2 ±5%, V4-watt, carbon film
Capacitor, 0.18)xF ±5%, 100-volt, metallized polyester
Installation and Operation Instructions
These instructions first discuss the reasons behind the NRSC requirements (starting on
the following page), then explain how to install the retrofit (on page 3).
Installation consists of replacing components on Cards #3 and #8, installing anew
card edge connector, setting jumpers, and plugging in anew circuit card. Asimple
de-emphasis circuit can be installed for off-air monitoring.
New operation information and technical notes follow the installation instructions. Also
included are field alignment and performance verification instructions, acircuit de-
scription, aparts list, aschematic, and an assembiy drawing for Card #1F10.
P/N 95302-000-04
lOO-FB-6/92 Orban, adivision of AKG Acoustics, Inc.
1525 Alvarado Street, San Leandro, California 94577 USA
Phone: [phone] FAX: [phone]

page 2RET-044 Instructions
Why the New NRSC Standard?
Over the years, as the North American air waves has become more crowded, interference
from first and second adjacent stations has become more and more of aproblem. Receiver
manufacturers responded by producing receivers with decreased audio bandwidth, so that an
adjacent station’s modulation extremes would not be audible as interference. This cutting
of the bandwidth had the effect of reducing the receiver’s high-frequency response, but it
was felt that lower fidelity would be less obnoxious than interference. As long ago as 1978,
Orban proposed and implemented pre-emphasis and low-pass filtering for AM broadcast to
provide brighter sound at the receiver while minimizing interference. This approach has
become widely accepted. Now the NRSC has formalized astandard which is acceptable to
all industry segments, and which can, if promptly implemented, result in avast improvement
in AM radio.
AM Stereo Introduces aPre-emphasis Dilemma
Certain AM receivers manufactured since 1984 for sale in North America, particularly those
designed for domestic AM stereo reception, have afrequency response that is substantially
wider than that of the typical mono AM receiver. The frequency response was widened largely
to enhance the sales potential of AM stereo by presenting adramatic, audible improvement
in fidelity in the showroom. As these new receivers became more prevalent, broadcasters
had to choose whether the station’s pre-emphasis would be optimized for the new AM 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 arelatively 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-emphasis and Low-pass Filtering
In response to this dilemma, the National Radio Systems Committee (NRSC) undertook the
difficult task of defining avoluntary recommended pre-emphasis curve for AM 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).
After ayear of deliberation, a‘modified 75-microsecond’ pre-emphasis/de-emphasis standard
was approved. This provides amoderate 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 asharp upper limit of lOkHz 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 acomplete
re-allocation of the AM band! The practical effect of widespread implementation of the
lOkHz standard is that lOkHz radios will then be feasible, and the bandwidth perceived by
the average consumer (now limited by the receiver to 3kHz, typically) will be dramatically
improved. On much mass-market consumer equipment, it will be difficult to tell AM from
FM.

RET-044 Instructions page 3
On April 27, 1989, The FCC (U.S.A.) released aReport and Order that amended section
73.44 of the FCC Rules by requiring all U.S. AM stations to comply with the occupied
bandwidth specifications of the NRSC-2 standard by June 30, 1990. The NRSC-2 standard is
an ‘RF mask’ that was derived from the NRSC-1 audio standard by the NRSC. The purpose
of the NRSC-2 RF mask is to provide atransmitted RF occupied bandwidth standard that any
station with aproperly-operating transmitter will meet, provided thatNRSC-1 audio processing
is used prior to the transmitter, and provided that the station is not over-modulating.
The Report and Order provides for ‘presumptive compliance’ with the NRSC-2 occupied
bandwidth standard: Prior to June 30, 1994, any station whose audio complies with the
NRSC-1 standard (an audio standard) is presumed to comply with the NRSC-2 standard (an
RF occupied bandwidth standard), unless the station receives an Official Notice of Violation
or aNotice of Apparent Liability from the Commission alleging non-compliance with the
NRSC-2 occupied bandwidth standard.
Orban welcomes the FCC’s decision: The radio manufacturers participating in the NRSC
stated emphatically that reduction in interference must be demonstrated by broadcasters be-
fore receiver manufacturers would be willing to release true wideband (lOkHz audio band-
width) 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.
It would therefore be wise to strictly conform to the standard even if it were not required by the
FCC. We are convinced that use of this more modest pre-emphasis and sharp lOkHz 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 AM 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
In these instructions “OPTIMOD-AM” refers to either of Models 9000A or 9000A/1. For
the purposes of this retrofit, your unit should be considered to be a“9000A/1” if there are
DAY and NIGHT indicators and axmtr eq switch on the right side of the subpanel; if these
are not present, you have a“9000A.” (Use the presence or absence of the XMTR EQ switch
and LEDs to determine your model number for this retrofit —some units labeled “9000A”
have been upgraded to 9000A/1 units.)
You will need aset of tools suitable for printed circuit board repairs. Refer to the drawings
in your OPTIMOD-AM Operating Manual for location of parts. All parts needed for this
retrofit are supplied in this kit.
Allow about 2hours for this retrofit.
CAUTION: The reliability of your unit can be compromised by poor workmanship. Refer to
“Replacement of Components on Printed Circuit Cards’’ in Section 4of your OPTIMOD-AM
Operating Manual (page 4-4 in the 9000A Manual, page 4-13 in the 9000A/1 Manual) for
instructions on how to rework the cards without damaging them or making them unreliable.

page 4RET-044 Instructions
1) Open the front panel of OPTIMOD-AM, remove the subpanel.
a) Disconnect OPTIMOD-AM, remove it from the rack, and place it on awork bench.
b) Remove the three screws at the top of the front panel, then tilt the hinged front panel
downward to reveal the interior.
c) Set the AC power switch to OFF.
d) Loosen the four DZUS fasteners on the subpanel by turning each 'A-tum counterclock-
wise with along Vi6-inch or 'A-inch flat-blade screwdriver.
e) 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.
NOTE: Due to mechanical interference. Cards #3 and #5 must be removed before
Cards #4 and #6 can be removed. (There is, however, no need to remove Card
#4 or #6 for this retrofit.)
2) Remove and replace components on Card #3.
a) Remove Card #3 from its slot.
b) Remove and replace the following components on Card #3.
This step modifies OPTIMOD-AM’s “input conditioning filter” on Card #3 to
obtain “modified 75gs” pre-emphasis.
Remove: Replace with the supplied:
C305 (4700pF capacitor)
C307 (160pF mica capacitor)
R309 (35.7K resistor)
R310 (28.0K resistor)
R311 (28.0K resistor)
R312 (4.53K resistor)
—(discard C305) —
1300pF ±2% mica capacitor
5.49K resistor (green-yellow-white-brown-brown)
8.66K resistor (gray-blue-blue-brown-brown)
8.66K resistor (gray-blue-blue-brown-brown)
3. 16K resistor (orange-brown-blue-brown-brown)
c) Remove and replace the following components on Card #3.
This step retunes the high-pass filter within the “input conditioning filter” from
lOOHz to 50Hz. These changes are not required by the NRSC standard, but
are strongly recommended by Orban to improve the audible bass quality of the
processing.
Remove:
R304 (24.9K resistor)
R305 (634K resistor)
R306 (4.99K resistor)
1C302 (RC4558)
Replace with the supplied:
49.9K resistor (yellow-white-white-red-brown)
1.27meg resistor (brown-red-violet-yellow-brown)
lO.OK resistor (brown-black-black-red-brown)
TL072
Be sure that the IC chip is correctly oriented in its socket, with the notch or dot
on the chip on the same side as the “tab” on the circuit board foil pattern.
d) Cormect the supplied O.lpF polyester film capacitor in parallel with resistor R345 on
Card #3.
This step makes the operation of the Broadband Compressor smoother by de-
emphasizing its control sample (so that it sees a“flat” signal and does not produce
unnatural gain reduction on program material rich in high frequencies). This
modification is not required by the NRSC standard, but is recommended by Orban.
e) Return Card #3 to its slot.

RET-044 Instructions page 5
3) Cut jumper, install Jumper and resistor on Card #8 {with xmtr eq switch).
[Skip this step unless your OPTIMOD-AM has DAY and NIGHT indicators and a XMTR EQ
switch on the right side of the subpanel and your Card #8 is Assembly Number 30381-000-
02.]
There are three versions of Card #8: one with transmitter equalization, one with-
out, and one with Assembly Number 30381-000-02 (The assembly number is
located on the solder side of the card).
a) Remove Card #8 from its slot.
b) Verify that jumper 2on Card #8 is in the “DAY ONLY” position (unless you have a
NIGHT filter installed on Card #8, and you want to continue using it at night).
See Fig. 1for jumper location.
c) Cut and remove the jumper labeled “3” on the Card #8 assembly drawing in the
9000A/1 Operating Manual.
This jumper is located very close to finger 20 on the card’s edge.
d) On the solder side of the card, solder one end of the supplied jumper wire to pin 7of
IC804’s socket (-2.0VDC clipper bias source).
e) Solder the other end of that wire to finger Lof the card edge connector.
Finger Lis the tenth pin down from the top, counting finger Aas the first finger.
Note that G, I, O, and Qare skipped in the labeling sequence.
Use only atiny amount of solder, and solder to the very inner edge of the finger
to avoid contaminating the gold mating surface of the finger with solder. Clean
away any flux residue with solvent.
f) Solder the supplied 75.OK (vioiet-green-biack-red-brown) resistor between pins 1and 3of
R817, the large OUTPUT ATTENuator control.
Fig. 1;Jumper Position, Card #8 (with transmitter equalization)

page 6RET-044 Instructions
4) Cut jumper and install resistor on Card #8 {without xmtr switch).
[Skip this step ifyour OPTIMOD-AM has DAY and NIGHT indicators and aXMTR EQ switch
on the right side of the subpanel, or ifyour Card #8 is Assembly Number 30381-000-02.]
There are three different versions of Card #8: one with transmitter equalization,
one without, and one with Assembly Number 30381-000-02 (The assembly num-
ber is located on the solder side of the card).
a) Remove Card #8 from its slot.
b) Cut and remove the jumper labeled “STEREO OPTION JUMPER” on the Card #8
assembly drawing in the 9000A Operating Manual.
This Jumper is located very close to pin 20 on the card edge connector.
c) Solder the supplied 75.OK (violet-green-black-red-brown) resistor between pins 1and 3of
R817, the large OUTPUT ATTENuator control.
d) Return Card #8 to its slot.
5) Cut trace, and install resistor on Card #8 {with Assembly Number30381-000-02).
[Skip this step ifyour Card #8 is not Assembly Number 30381-000-02.]
There are three versions of Card #8: one with hansmitter equalization, one with-
out, and one with Assembly Number 30381-000-02 (The assembly number is
located on the solder side of the card).
a) Remove Card #8 from its slot.
b) Cut the trace between point 2and the adjacent trim pot.
c) Connect point 2to edge connector pin 20.
d) Connect the trim pot terminal disconnected in step 1to edge connector pin 19.
e) Return Card #8 to its slot.
6) Install edge connector and card guides for slot #1.
a) Remove the 30 screws that attach the top cover to the chassis, then lift off the top
cover.
b) Remove the eight screws that attach the bottom cover to the rear panel.
c) Set the unit on apadded surface with the rear panel facing you and the bottom cover
down.
Leave about 6inches (15cm) between the rear panel and the edge of the table.
Be sure the AC power cord is unplugged.
d) Remove the nine screws in three vertical groups on the rear panel.
One group of three is located at the left edge of the rear panel, one on the right
edge. The third group is located about one-third of the way from the right edge.

RET-044 Instructions page 7
e) Very carefully pull the rear panel about %-inch (2cm) 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.
f) Attach the supplied edge connector to the circuit card cage at the rear of what will be
slot #1 (to the left of Card #2) with the supplied screws and nuts.
Use the other edge connectors as models for installation.
g) Working from the front of the unit, pop the two plastic card edge guides into their
supports at the top and bottom of the card cage.
Again, use the existing guides as models.
h) Ifyou have aOPTIMOD-AM with transmitter equalization, connect the wires from the
edge connector you just installed to the other edge connectors as follows.
[Skip to step iunless your OPTIMOD-AM has DAY and NIGHT indicators and a
XMTR EQ switch on the right side ofthe subpanel.]
The 9000A/1 employs wire-wrap connections. To connect awire, wrap it over
and solder it near the end of the indicated wire-wrap pin.
The pins may be numbered on the connector body. If not, count down from the
top. Alphabetic pins are those in the left row (the side furthest from the power
supply). When counting alphabetic pins, skip G, I, O, and Q. To avoid errors,
first mark the tip of every pin to be connected with afelt tip pen, then check the
marks again before beginning work.
Connect wire from: To: Function:
slot #1, pin Ascrew at top of slot #2 chassis ground
slot #1, pin Bslot #2, pin 2+15VDC
slot #1, pin Cslot #2, pin 3circuit ground
slot #1, pin Eslot #2, pin 5-15VDC
slot #1, pin Tslot #8, pin JNIGHT logic
slot #1, pin Uslot #8, pin L-2.0VDC clipper bias
slot #1, pin Vslot #8, pin 7-t-2.0VDC clipper bias
slot #1, pin Xslot #8, pin 19 Card #1F10 audio output
slot #1, pin Yslot #8, pin 20 Card #1F10 audio input

page 8RET-044 Instructions
i) Ifyou have aOPTIMOD-AM without transmitter equalization, connect the wires from
the edge connector you just installed to the other edge connectors as follows.
[Skip to step jifyour OPTIMOD-AM has DAY and NIGHT indicators and aXMTR
EQ switch on the right side of the subpanel.]
The 9000A employs wire-wrap connections. To connect awire, wrap it over and
solder it near the end of the indicated wire-wrap pin.
The pins may be numbered on the connector body. If not, count down from the
top. Alphabetic pins are those in the left row (the side furthest from the power
supply). When counting alphabetic pins, skip G, I, O, and Q. To avoid errors,
first mark the tip of every pin to be connected with afelt tip pen, then check the
marks again before beginning work.
Connect wire from: To: Function:
slot #1, pin Ascrew at top of slot #2 chassis ground
slot #1, pin Bslot #2, pin 2+15VDC
slot #1, pin Cslot #2, pin 3circuit ground
slot #1, pin Eslot #2, pin 5-15VDC
slot #1, pin Tslot #8, pin 3circuit ground
slot #1, pin Uslot #8, pin 6-2.0VDC clipper bias
slot #1, pin Vslot #8, pin 7+2.0VDC clipper bias
slot #1, pin Xslot #8, pin 19 Card #1F10 audio output
slot #1, pin Yslot #8, pin 20 Card #1F10 audio input
Check all your work very carefully by retracing all steps. Look for solder bridges.
k) 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.
l) Replace the 9rear-panel screws removed above.
Do not tighten screws until all screws are loosely in place, and the flanges of the
rear panel are aligned with those of the side panels.
m) Replace the top cover and the 30 screws that hold it in place.
Replace all screws loosely before tightening them. For best RFI protection, replace
and firmly tighten all screws.
n) Replace the eight screws that attach the bottom cover to the rear panel.

RET-044 Instructions page 9
7) Install Card #1F10.
NOTE: The “12kHz” positions of Card #1F10 in fact bypass all filters on the card.
Since the nominal bandwidth of the 9000A or 9000A/1 is llkHz without further
filtering, read “llkHz” whenever you see “12kHz” in the following text.
Card #1F10 contains the sharp lOkHz low-pass filter necessary to restrict the output
spectrum of the processor within NRSC standards. It also contains a5kHz 30dB/octave
low-pass filter (for international use). When jumpers Aand Bare in the “12kHz” position,
the 5kHz and lOkHz filters are bypassed (and OPTIMOD-AM’s built-in llkHz band
limiting remains in effect). In the 9000A/1 (but not in the 9000A), Card #1F10 follows
the DAY/NIGHT logic on Card #8.
a) Position jumper A(day) on Card #1F10 to select the low-pass filter (see Fig. 2).
You may select 5kHz, lOkHz, or 12kHz low-pass filtering in any combination for
day and night operation. The NRSC standard specifies lOkHz low-pass filtering
for both day and night.
IMPORTANT: The 9000A is always in the DAY mode. Select low-pass filtering
with jumper A(jumper Bhas no effect).
b) Insert Card #1F10 into slot #1.
#1F10 OO 5kHz —-OO
lo oH—10kHz —
-
|o o| NRSC (as shipped)
oo-—12kHz —o o
JUMPERS JUMPER A
NIGHT DAY
(inactive on 9000A)
Fig. 2: Low-pass Filter Jumper Positions. Card #1F10

page 10 RET-044 Instructions
8) Replace subpanel and close the front panel.
The subpanel should always be replaced, since it is an integral part of the chassis RFI pro-
tection.
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 ’/4-tum clockwise.
The DZUS fasteners turn only 'A-tum. Don’t force them, lest they be damaged
in away that is very time consuming to repair.
c) Set the internal AC power switch to ON.
d) Raise the front panel and fasten the three screws that secure it in place.
e) Return OPTIMOD-AM to its rack, connect and ground unit.
9) Attach the supplied “Special Modification” label to the rear panel.
10)
Install NRSC de-emphasis circuit.
Asimple de-emphasis circuit can be placed between the audio output of the modula-
tion monitor and the input of the monitor amplifier to provide complementary 75ps de-
emphasis. For amore precise simulation of a“standard” NRSC receiver (including a
lOkHz notch filter to reduce any audible artifacts that might result from ringing introduced
by the very sharp lOkHz low-pass filter, and to eliminate lOkHz whistles encountered in
off-air monitoring), we recommend our ACC-023 NRSC Monitor Rolloff Filter.
See Fig. 3for aschematic 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 600 ohms, and that resistors
or pads may have to added to achieve this.
Modulation Monitor Monitor Rolloff Filter Monitor Amp or D.A.
Fig. 3: NRSC Simplified 75ps Monitor Rolloff Filter Schematic

RET-044 Instructions page 11
Operation
No alignment or adjustment of OPTIMOD-AM following this retrofit is required. However,
if the NRSC pre-emphasis has significantly reduced the amount of pre-emphasis that you are
using, you may find that it is possible to get greater loudness by advancing the setting of the
CLIPPING and/or SMART CLIPPER DRIVE controls without increasing distortion objectionably.
Note that all OFTIMOD-AM controls may be set as they were prior to installation of *e
modification, except for the 5kHz EQ and lOkHz EQ controls (which must both be set to “0”),
and the INPUT FILTER switch (which must be set to IN).
Technical Notes
Fig. 4shows the normal input-to-output swept frequency response of an OPTIMOD-AM
in PROOF mode with Retrofit Kit RET-044 properly instaUed. You may wish to check the
operation of your unit against this figure.
Fig. 5shows the normal response of Card #3 from the processor input terminals to finger 6
of Card #3. Fig. 5is auseful reference against which to check the success of your Card #3
modifications.
Fig. 12 shows the typical output power spectrum of OPTlMOD-AM when the NRSC mod-
ification has been successfully installed. This is a0—20kHz linear measurement using an
FFT spectrum analyzer in its “peak hold” mode over a20-minute period with bright program
material.
OPTIMOD is aregistered trademark of Orban, adivision of AKG Acoustics, Inc.

page 12 RET-044 Instructions
III
30Hz 1kHz 20kHz
Fig. 4: Swept Frequency Response, Input-to-Output, 30-20,OOOHz
Fig. 5: Card #3 Frequency Response, 20-20,000Hz

RET-044 Instructions page 13
Field Alignment and Performance Verification
-Card#lF10
Use thefollowing procedure to align and verify performance of Card #1F10 after the card has
been repaired.
This procedure is not requiredfor 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 ajumper, so the Jumpers can be returned
to these positions when you are finished.
Jumper and component locations are shown in the Card #1F10 assembly drawing at the
end of these instructions.
In amono OPTIMOD-AM, all connections are to the left input or output.
Always turn off the power to OPTlMOD-AM 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 lOkHz low-pass filters
-checking DC servo operation
-adjusting the gain of the lOkHz low-pass filter
-adjusting the notch frequency of the lOkHz low-pass filter
-verifying distortion and noise performance
Follow instructions in the order given, without skipping steps.
NOTE: The “12kHz” positions of Card #1F10 in fact bypass all filters on the card.
Since the nominal bandwidth of the 9000A or 9000A/1 is llkHz without further
filtering, read “llkHz” whenever you see “12kHz” in the following text.

page 14 RET-044 Instructions
Equipment required:
Low-frequency spectrum analyzer with tracking generator
Tektronix 5L4N plug-in with 5111 bistable storage mainframe, or equivalent. Alter-
natively, asweep 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. xlO probe.
Audio oscillator
Residual distortion less than 0.0015%.
Frequency counter
Accurate to ±0.05%
Total harmonic distortion (THD) analyzer
Residual distortion less than 0.0015%.
Audio voltmeter
Accurate to +2%. (Sound Technology 1700 A/B or 1710, for example.)
Pink noise generator
Digital voltmeter
Accurate to ±0.1%.
It is assumed that the technician is thoroughlyfamiliar with 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-AM must, however, be off the air during this
procedure.
a) Remove the three screws at the top of the front panel, then tilt the hinged front panel
downward to reveal the interior.
b) Loosen the four DZUS fasteners on the subpanel by turning each '/t-tum counterclock-
wise with along Vi6-inch or >/
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.

RET-044 Instructions page 15
2)
Extend Card #1F10.
Remove Card #1F10, insert acard extender into slot #1 of OPTIMOD-AM’s card cage,
and then plug Card #1F10 into the extender card.
3)
Set controls.
a) Record the current settings of your OPTIMOD-AM.
b) Set the controls as follows;
EQUALIZER OUT
CLIPPING 5
SMART CLIPPER DRIVE 5
MODE OPERATE
9100A/1 only: XTMR EQ OUT
Don’t change the positions of the other controls.
4) Verify DC voltages.
Measure voltages against circuit ground (available at pin Cof the edge connector on Card
#1F10.).
a) Set the mode switch to operate.
b) Turn the POS PEAK THRESH control fully counterclockwise.
c) Measure the voltage at the anode of diode CR2 on Card #1F10 to verify that it is -2.0
volts DC, ±0.2V.
d) Measure the voltage at the cathode of diode CRl on Card #1F10 to verify that it is
+2.0 volts DC, ±0.2V.
e) Set the mode switch to proof.
f) Measure the voltage at the anode of diode CR2 on Card #1F10 to verify that it is
approximately -14 volts DC.
g) Measure the voltage at the cathode of diode CRl on Card #1F10 to verify that it is
approximately +14 volts DC.
NOTE; In the following, ignore instructions to move jumper B(night) if your OPTIMOD-AM
does not have day and NIGHT indicators and aXMTR EQ switch on the right side of the
subpanel. If it does not, only Jumper A(day) is active in your unit.
5) Verify performance of the 5kHz low-pass filter, and of “bypass.”
In “bypass”, llkHz low-pass filtering is provided by other OPTIMOD-AM cards.
a) Connect the output of asweep or tracking generator to OPTIMOD-AM’s input.
b) Connect the input of aspectrum analyzer or oscilloscope to TP2 on Card #1F10.
c) Place Jumpers A(day) and B(night) on Card #1F10 in the “12kHz” position.

page 16 RET-044 Instructions
d) Verify that response is approximately flat to llkHz.
Be sure that the sweep level is low enough to avoid clipping by OPTIMOD-AM
circuitry.
e) Place jumpers A(day) and B(night) on Card #1F10 in the “5kHz” position.
f) Verify that response is flat +ldB to 5.0kHz, and rolls off with aslope of greater than
30dB/octave above 5kHz.
It is normal to see aslight “glitch” at lOkHz about -30dB.
g) Ifyou have a9000AOPTIMOD-AM, skip to step 6.
If you have a9000A/1, continue.
h) Place jumper A(day) on Card #1F10 in the “12kHz” position.
i) Verify that the 5kHz low-pass filter is activated when the TX EQ DAY/NIGHT switch is
moved to the NIGHT position.
If the filter is operating, you will see asteep rolloff of frequencies higher than
5kHz, as above.
j) Verify that the 5kHz low-pass filter is deactivated when the TX EQ DAY/NIGHT switch
is moved to the DAY position.
If the filter is inactive, you will not see asleep rolloff above 5kHz.
k) On Card #1F10, place jumper B(night) in the “12kHz” position, and jumper A(day)
in the “5kHz” position.
l) Verify that the 5kHz low-pass filter is activated when the TX EQ DAY/NIGHT switch is
moved to the DAY position.
m) Verify that the 5kHz low-pass filter is deactivated when the TX EQ DAY/NIGHT switch
is moved to the night position.
n) Disconnect the sweep or tracking generator and spectrum analyzer or oscilloscope from
OPTIMOD-AM.
6) Check DC servo operation.
a) Place jumper A(day) and B(night) on Card #1F10 in the “lOkHz” position.
b) With adigital voltmeter, verify that the DC offset is less than 15mV at TP2.
7) Adjust lOkHz low-pass filter gain.
a) On Card #1F10, place jumper A(day) in the “12kHz” position.
b) Connect an audio oscillator to OPTlMOD-AM’s input.
c) Set OPTIMOD-AM’s VU meter selector to SMART CLIPPER.
d) Set the audio oscillator to IkHz, and adjust its output level until OPTIMOD-AM’s VU
meter reads approximately “-6VU.”
e) Ifyou have a9000AII, set OPTIMOD-AM’s TX EQ DAY/NIGHT switch to DAY.
Skip to step fif your OPTIMOD-AM is a9000A.

RET-044 Instructions page 17
f) Observe the level at TP2. Make anote of it.
g) On Card #1F10, place jumper A(day) in the “lOkHz” position.
h) Adjust trimmer R62 until the level at TP2 is the same (+0.1dB) as that observed in
step f, above.
8) Adjust frequency of the first lOkHz low-pass filter’s notch.
a) Set the audio oscillator for 10,100Hz +10Hz, and check the frequency with acounter.
The audio oscillator should still be connected to OPTIMOD-AM’s input.
Do not change the audio oscillator’s output level.
b) While observing TP2 with an audio voltmeter, adjust trimmer R17 to null the signal.
The null should be more than 45dB below the “flat” (below 9kHz) level observed
in step 7f.
c) Disconnect the audio oscillator and voltmeter from OPTIMOD-AM.
9) Verify lOkHz low-pass filter performance.
a) Connect the output of the sweep or tracking generator to OPTIMOD-AM’s input.
b) Connect the input of the spectrum analyzer or oscilloscope to TP2.
c) Verify that response is flat +1.0dB, -2.0dB to 9600Hz, and rolls off with aslope of
greater than 60dB/octave above lOkHz.
Be sure that the sweep level is low enough to avoid clipping by OPTlMOD-AM
circuitry.
d) Ifyou have a9000A OPTIMOD-AM, skip to step 10.
If you have a9000A/1, continue.
e) Place jumper A(day) on Card #1F10 in the “12kHz” position.
f) Verify that the lOkHz low-pass filter is activated when the TX EQ DAY/NIGHT switch is
moved to the night position.
If the filter is operating, you will see avery steep rolloff of frequencies higher
than lOkHz.
g) Verify that the lOkHz low-pass filler is deactivated when the TX EQ DAY/NIGHT switch
is moved to the DAY position.
If the filter is inactive, you will not see asteep rolloff above lOkHz.
h) On Card #1F10, place jumper B(night) in the “12kHz” position, and jumper A(day)
in the “lOkHz” position.
i) Verify that the lOkHz low-pass filter is activated when the TX EQ DAY/NIGHT switch is
moved to the day position.
j) Verify that the lOkHz low-pass filter is deactivated when the TX EQ DAY/NIGHT switch
is moved to the night position.
k) Disconnect the sweep or tracking generator and spectrum analyzer or oscilloscope from
OPTIMOD-AM.

page 18 RET-044 Instructions
10) Restore all jumpers to the positions they were in at the beginning of this align-
ment and performance verification procedure.
11) Remove the card extender and return Card #1F10 to slot #1.
12) Replace subpanel, close front panel.
The subpanel should always be replaced, since it is an integral part of the chassis RFI pro-
tection.
a) Disconnect all test instruments from OPTIMOD-AM.
b) Taking cate 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 'A-turn clockwise.
The DZUS fasteners turn only '4-tum. Don’t force them, lest they be damaged
in away that is very time consuming to repair.
d) Set the internal AC POWER switch to ON.
e) Raise the front panel and fasten the three screws that secure it in place.
13) Restore all controls to their settings prior to beginning this alignment and per-
formance verification procedure.

page 20 RET-044 Instructions
Circuit Description —Card #1F10
Card #1F10 is divided into two “subsystems”, which are described below in order of signal
flow. The block diagram in Fig. 6illustrates this description.
1) 5kHz Low-Pass Filter
This is aunity-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 athird-order non-inverting filter with agently rolled-
off frequency response. The 5th-order filter’s frequency response shaping is completed by
IC9a and associated components, which fomi a2nd-order inverting filter when the circuit
path is completed by strapping jumper A(DAY) or B(NIGHT) to the “5kHz” position.
lC8b and associated components form aphase 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.
DAY/NIGHT switching is effected by very simple logic. Pin Ton the card is low (-15V)
when OPTIMOD-AM is in NIGHT mode, and high (ground) when it is in DAY mode. The
logic level at pin Tdrives JFET Q2 directly. Q1 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 Binto the circuit path, while Q2 turns on in DAY
mode, and connects jumper Ainto the circuit path.
2) lOkHz (NRSC) Low-Pass Filter
The signal can be routed to alOkHz 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 CRl, CR2, which provides main
peak control for the signal. After buffering by ICla, the clipped signal is applied to the
first lOkHz filter IC2, IC3, IC4 (and associated components). This filter is very steep, and
removes the harmonics introduced by the clipping in CRl, CR2, as well as any significant
program energy above lOkHz.
The first filter is an active-RC analog of apassive LC ladder filter. It is realized by resistors,
capacitors, and frequency-dependent negative resistors (FDNRs). An 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 aseries resistor to create anotch in the frequency response of
the filter. (This is analogous to aseries 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 anotch at 12.00kHz ±4%.
The circuit associated with IC4 is tuned by R39 to produce anotch at precisely lO.lOkHz to
ensure that the filter’s response falls accurately above lOkHz, and that NRSC specifications
are met.