Inovonics 540 Manual
—–USER’S RECORD —–
Model 540 -Serial No. _______
Date Purchased _____________
Warranty Card Mailed —¨
OPERATING AND MAINTENANCE
INSTRUCTION MANUAL
MODEL 540
RDS/RBDS RADIODATA ENCODER
January, 1998
(Effective with Serial No. 026)
1305 Fair Avenue •Santa Cruz, CA 95060
TEL: (408) 458-0552 • FAX: (408) 458-0554
Visit our Website: www.inovon.com
——
1
TABLE OF CONTENTS
Section I -INTRODUCTION
Model 540 Product Description ...............................................................................................3
General -FCC Type Acceptance -Features
Model 540 Technical Specifications........................................................................................4
Block Diagram ...........................................................................................................................5
Section II -INSTALLATION
Unpacking and Inspection .......................................................................................................6
Mounting ....................................................................................................................................6
Rack Requirements -Heat Dissipation
AC (Mains) Power .....................................................................................................................6
As Delivered -Voltage Selector -Power Cord
Radio Frequency Interference (RFI) .....................................................................................7
Location -Ground Loops
Jumpering Options) ..................................................................................................................7
Section III -SETUP AND OPERATION
Panel Controls and Indicators .................................................................................................9
Meter Select -Subcarrier Tuning -Filter -SCA Audio -
Phones -Power
MPX Input and Level Set ........................................................................................................10
Input Connection -Correcting for Response Errors -Input Level
Adjustment
Section IV -RDS-DECODE OPTION
Installing the Optional Plug-in RDS Card ............................................................................12
Computer Requirements .......................................................................................................12
Installing the Software ...........................................................................................................13
DOS-Based Computers -Computers Running Windows®
Running the DETECT Program ..............................................................................................13
——
2
Starting the Program Under DOS -Running Under Windows®-
The DETECT Screen -Data Error Display
Section V -CIRCUIT DESCRIPTIONS
Introduction .............................................................................................................................15
Navigating the Schematics -The “PIC” and Front-Panel Logic
Input Conditioning and First Two Conversions ..................................................................15
Input Stage and Band-Pass Filter -Programmable First LO -
First IF and Second LO
Second IF and SCA Demodulation .......................................................................................16
Second IF Filter -SCA Demodulator -De-Emphasis, Audio
Output and Monitoring
Third(!) Conversion ................................................................................................................17
LO and Mixer -IF Filtering
Metering ...................................................................................................................................17
Metering Selector -Meter Rectifier -Bargraph Display
RDS Option Plug-In Assembly ..............................................................................................18
Baud Rate Jumper
Power Supply ...........................................................................................................................18
Model 540 Calibration Procedures .......................................................................................19
R14: Input Gain and Flatness Check -R19 and R64: Injection
and Data Level Set -R20: SCA Deviation -R21: SCA Audio
Level Set
Section VI -APPENDIX
Parts Lists -Schematics -Warranty .................................................................................21
——
3
Section I
INTRODUCTION
MODEL 540 PRODUCT DESCRIPTION
GeneralInovonics’ Model 540 enables accurate measurement and monitoring of
FM broadcast subcarriers. These may include speech and music “SCA”
(Subsidiary Carrier Authorization) transmissions, “RDS” (Radio Data
System) information, and various existing-and-proposed “high-speed”
digital services which provide paging and other one-way data
communications.
The 540 accepts the demodulated FM “baseband” signal feed from any
Modulation Monitor. It is frequency-agile, tuning any subcarrier
frequency between 54kHz and 99kHz with digital precision. Bargraph
metering displays subcarrier injection, as well as subcarrier deviation
for SCA audio transmissions. Demodulated SCA audio may be
monitored with headphones and is available at a rear-panel connector
as well.
FCC Type
Acceptance Equipment for monitoring broadcast transmissions in the U.S. no
longer requires “type acceptance” by the Federal Communications
Commission. Though rules pertaining to monitoring equipment have
been relaxed or abandoned, the broadcaster remains responsible in
ensuring that his transmitted signal conforms to current FCC
regulations.
Features Features of the Inovonics 540 include:
•Works with any FM Mod-Monitor having a composite-
baseband (MPX) output. Easily calibrated with built-
in CAL facility.
•Measures injection level of SCA, RDS and high-speed
data subcarriers.
•Demodulates audio SCAs and accurately displays
subcarrier deviation.
•Triple-conversion design with precise, crystal-
controlled digital tuning. Dual IF bandwidth gives
optimum selectivity.
•An optional RDS data decoder module is available, and
is supplied with comprehensive radio-data analysis
software.
——
4
MODEL 540 TECHNICAL SPECIFICATIONS
Subcarrier Tuning Range:
54kHz to 99kHz in 1kHz
increments.
Subcarrier Injection
Measurement:
a:±1kHz to ±10kHz of main
carrier deviation with ±250Hz
resolution.
b: 1% to 13% of main carrier
modulation with 1/3% reso-
lution (100% modulation
equivalent to ±75kHz
deviation).
Measurement Bandwidth:
WIDE: 12kHz filter for SCA and
certain high-speed data
channels.
NARROW: 3.5kHz filter for RDS
and similar narrowband data
channels.
SCA Deviation Measurement:
Absolute: ±1kHz to ±10kHz
audio subcarrier deviation
with ±250Hz resolution
Relative: dB scale indicates
–20dB to +2.5dB. “0dB” is
factory-set to ±5kHz devia-
tion; may be recalibrated by
user.
Calibration Provision:
Total, main-channel carrier
deviation is monitored in the
CALIBRATE mode and adjusted to
reflect the station’s primary
Modulaton Monitor readings.
Metering:
The 38-segment bargraph display
is peak-responding and
incorporates a peak-hold feature.
SCA Audio Response:
±0.5dB, 50Hz to 5kHz. Switch
selection of FLAT or 150-micro-
second DE-EMPH(asis).
SCA Distortion and Noise:
Better than 40dB, unweighted,
below ±5kHz deviation.
Audio Outputs:
a: Rear-panel, active-balanced
SCA program output.
b: Front-panel headphone jack
monitors SCA audio, switches
to main channel (mono) in
CALIBRATE mode.
Composite (MPX) Input:
Unbalanced, bridging; requires
1V p-p or greater signal equivalent
to ±75kHz main channel
deviation.
RDS Decoder Option:
A plug-in module formats raw RDS
data to RS-232. Supplied software
enables detailed RDS data analysis
with any IBM-compatible PC.
Power Requirements:
105–130VAC or 210–255VAC,
50/60Hz; 15 watts.
Size and Weight:
1¾”H x 19”W x 7”D (1U);
7 lbs. (shipping).
——
5
BLOCK DIAGRAM
A simplified Block Diagram of the Model 540 is shown in Figure 1,
below. Monitor circuitry is detailed in the Circuit Descriptions section
beginning on Page 15. These descriptions reference Schematic
Diagrams found in the Appendix.
Figure 1 -Block Diagram, Model 540 FM Subcarrier Monitor/Demod
MPX
INPUT 50kHz-100kHz
BANDPASS
INPUT
GAIN FIRST MIXER
455kHz
BAND-PASS
SECOND MIXER
25kHz
BAND-PASS
SYNTHESIZER
CONTROLLER SYN.
LO
67
SUB.
TUNING
480kHz
LO
DOUBLING
MONOSTABLE 5kHz
LOW-PASS SCA
DE-EMPHASIS
25kHz
LO
3kHz
LOW-PASS M
E
T
E
R
I
N
G
S
E
L
E
C
T
O
R
METER
RECT. METER
INTEG.
MAIN CHAN.
DE-EMPHASIS
BALANCED
SCA AUDIO
PHONES
DE-EMPH
FLAT
SCA
THIRD
MIXER
FILTER
WIDE
NAR-
ROW
BALANCING AMP
HEADPHON
E
FM DEMOD LIMITING
BARGRAPH
——
6
Section II
INSTALLATION
UNPACKING AND INSPECTION
Immediately upon receipt of the equipment, inspect carefully for any
shipping damage. If damage is suspected, notify the carrier at once, then
contact Inovonics.
It is recommended that the original shipping carton and packing
materials be set aside for future reshipment. In the event of return for
Warranty repair, shipping damage sustained as a result of improper
packing for returnmay invalidate the Warranty!
IT IS VERY IMPORTANT that the Warranty Registration
Card found at the front of this Manual be completed and
returned. Not only does this assure coverage of the equip-
ment under terms of the Warranty, and provide some means
of trace in the case of lost or stolen gear, but the user will
automatically receive specific SERVICE OR MODIFICA-TION
INSTRUCTIONS should they be issued by Inovonics.
MOUNTING
Rack
Requirement The Model 540 Monitor mounts in a standard 19-inch equipment rack
and requires only 1¾ inches (1U) of vertical rack space. Plastic
“finishing” washers will protect the painted finish around the
mounting holes.
Heat
Dissipation Consuming about the same power as a single string of Christmas
“twinkle” bulbs, the 540, itself, generates negligible heat. The unit is
specified for operation within an ambient temperature range extending
from freezing to 120°F/50°C. Because adjacent, less efficient
equipment may radiate substantial heat, be sure that the equipment
rack has sufficient ventilation to keep internal temperature below the
specified maximum.
AC (MAINS) POWER
As delivered
Unless specifically ordered for export shipment, the Model 540 is set at
the factory for operation from 115V, 50/60Hz AC mains. The rear-panel
designation next to the fuseholder will confirm both the mains voltage
——
7
designation next to the fuseholder will confirm both the mains voltage
selected and the value of a proper fuse.
Voltage
Selector A mains voltage selector switch is located beneath the top cover of the
unit, close to the AC mains connector on the circuit board. With
primary AC power disconnected,you may slide the red actuator with a
small screwdriver so that the proper mains voltage designation (115 or
230) shows. Be certain always to install an appropriate fuse, and check
that the rear-panel voltage/fuse designation is properly marked. It is
factory practice to cross-out the inappropriate designation with an
indelible black marking pen. You can remove this strikethrough with
lacquer thinner or a similar, probably carcinogous solvent to
redesignate.
BE SURE that the mains voltage selector setting and pri-
mary fuse value are appropriate for the mains supply before
plugging the 540 Monitor into the wall outlet.
Power Cord The detachable IEC-type power cord supplied with the Monitor is fitted
with a North-American-standard male plug. Nevertheless, the
individual cord conductors aresupposed to be color-coded in accordance
with CEE standards; that is:
BROWN = AC “HOT” BLUE = AC NEUTRAL GRN/YEL = GROUND
If this turns out not to be the case, we offer our apologies (cord vendors
sometimes lie to us) and advise that US color coding applies:
BLACK = AC “HOT” WHITE = AC NEUTRAL GREEN = GROUND
RADIO FREQUENCY INTERFERENCE ( R F I )
Location Although we have anticipated 540 installation in a broadcast
environment, you should practice care in locating the unit away from
abnormally high RF fields.
Ground Loops Because the input and the output of the Model 540 are chassis-ground-
referenced, a mains frequency or RF ground loop could be formed
between the input or output cable shield grounds and the AC power
cord ground. A “ground-lifting” AC adapter will probably remedy any
problem, though the chassis somehow must be returned to earth
ground for safety. Generally, being screwed-down in the equipment
rack will satisfy the safety requirement.
JUMPERING OPTIONS
The Model 540 has but a single jumpering option. It selects either 50µs
or 75µs de-emphasis for the monaural, main-channel program audio
——
8
which is routed to the front-panel PHONES jack in theCALIBRATION
mode.
The de-emphasis jumper strip is located to the left of IC28. The circuit
board legend identifies the “50” and “75” (microsecond) positions for
the movable jumpering shunt; this jumper will have been positioned
appropriately for the original shipping destination.
——
9
Section III
SETUP AND OPERATION
PANEL CONTROLS AND INDICATORS
This section starts with an overview of front-panel controls and
indicators. Please at least scan this section to verify that your
understanding is in agreement with our terminology.
METER
SELECT
This pair of up/down buttons cycles the Model 540
among its various monitoring functions. The
selected function is indicated by an attendant LED.
The functions are:
CALIBRATE –in this setup mode, metering and
audio monitoring is switched-over to a
measurement of total baseband modulation
(primary carrier deviation). The corresponding set
point (above the 10% scale designation) allows gain
to be adjusted such that this mark coincides with
full carrier modulation; that is, “100%” or ±75kHz
carrier deviation. For proper annotation in this
mode, multiply the indicated percentage or kHz-
deviation numbers by 10. (FS=130% or ±100kHz)
PERCENT INJECTION –this scale and the±kHz
INJECTION scale are active when measuring the
modulation contribution of the tuned subcarrier.
The 10% point on the upper scale is opposite the
±7.5kHz point on the one below, indicating the
relationship of these measurements to “full”
modulation; that is, 100% or ±75kHz carrier
deviation.
SCA ±kHz DEVIATION –this measurement option
displays the actual deviation of the audio-
modulated SCA subcarrier. It is a valid
measurement only for SCA, and is completely
meaningless for digital data subcarriers. This
measurement is not affected by SCA AUDIO (de-
emphasis) selection.
SCA AUDIO LEVEL –this is a relative, dB-calibrated
scale for measurement of SCA program levels, and
will reflect a FLAT or a DE-EMPH(de-emphasized)
SCA AUDIO selection. Factory calibration sets this
measurement to indicate “0dB” at an SCA
——
10
measurement to indicate “0dB” at an SCA
subcarrier deviation of ±5kHz, at a frequency
below the influence of de-emphasis. This
calibration may be reset for another reference if
desired, the procedure is given on Page 20.
SUBCARRIER
TUNING Use this pair of up/down buttons to tune the
subcarrier frequency. Press-and-release to tune up
and down in individual 1kHz steps, or hold the
button down to scan rapidly.
FILTER IF bandwidth is controlled by this switch. The
selected filter, WIDE (SCA), or NARROW (DATA), is
indicated by an attendant LED. Select theWIDE
mode for SCA and high-speed digital subcarriers.
RDS and similar low-data-rate services may be
crowded close to one another or to the main FM
baseband signal, inviting a NARROWfilter
selection.
SCA AUDIO Demodulated SCA audio may be monitored with
either a FLAT frequency characteristic, or with
standardized 150-micro-second DE-EMPH (de-
emphasis). The chosen audio characteristic will be
imparted to the front-panel PHONES jack, the rear-
panel SCA BALANCED AUDIO connector, and to
metering in theSCA AUDIO LEVEL (dB-scale)
measurement mode.
PHONES This stereo jack accommodates a pair of standard
headphones. In theCALIBRATE mode, a de-
emphasized baseband monaural program signal is
routed to this jack. In all other operating modes
the headphones will monitor the output of the
audio SCA demodulator. When an SCA channel is
tuned the audio subcarrier program will be heard.
RDS or other data channels will yield a noise
characteristic of a data signal. Since the subcarrier
is heard through an FM demodulator, thesound
may not have the anticipated character.
POWER Interests of national security forestall our
elaboration into the function of this switch.
MPX INPUT AND LEVEL SET
Input
Connection
Cable the rear-panel
COMPOSITE MPX INPUT
connector directly to the
composite, “baseband” output of the station’s Modulation Monitor.
Check the mod-monitor’s instruction manual to verify that its output
has a flat frequency characteristic, and that it provides at least one volt,
——
11
has a flat frequency characteristic, and that it provides at least one volt,
peak-to-peak, at 100% carrier modulation (±75kHz deviation).
Correcting for
Response
Errors
Subcarrier injection measurement accuracy is a function of mod-
monitor output flatness. If mod-monitor demodulation response
exhibits HF roll-off as it approaches 100kHz, use the manufacturer’s
published correction chart (or make one of your own!) to assure
accuracy of subcarrier injection readings.
The input impedance of the Model 540 is 100k-ohms, essentially an
open circuit. To obviate any need to address impedance matching or
source termination, keep the interconnecting cable as short as possible.
Input Level
Adjustment The 540 Monitor is most accurately calibrated by applying a steady-
state input signal equivalent to 100% carrier modulation; that is, a
carrier deviation of ±75kHz. If the mod-monitor has a built-in
calibrator which drives its own indicator to this figure, and if that same
test signal is delivered to the mod-monitor’s composite output
connection, calibration of the 540 is very easy. Simply adjust the 540’s
rear-panel INPUT GAIN control until the bargraph display reaches the
CALIBRATE mark on the scale. (This is directly above the “10%”
designation and corresponds to 100% carrier modulation.)
If the mod-monitor does not have a built-in calibration source, an
equally accurate adjustment may be made by driving the exciter to full
modulation with a test oscillator signal, probably best done during a
maintenance period. Set INPUT GAIN as described above.
Another calibration method allows you to use normal program material
for setup. TheINPUT GAIN control may be set with acceptable accuracy
by setting program peaks displayed in theCALIBRATE mode to the same
total-peak-modulation values indicated by the mod-monitor. In
CALIBRATE, multiply the Model 540’s scale markings by 10 to show
peak excursions of 10% to 130% modulation (10kHz to 100kHz carrier
deviation). Since 540 metering is peak-responding and incorporates a
peak-hold feature, it should indicate the same peak levels indicated by
the mod-monitor. However, if mod-monitor metering is not a true,
peak-responding display, defer instead to calibrated peak flasher set
points.
——
12
Section IV
RDS-DECODE OPTION
The Model 540 accommodates an optional plug-in assembly which
independently demodulates digital “radiodata” broadcast by stations
supporting RDS, the Radio Data System. RDS transmissions serve a
number of purposes: automatic receiver tuning to search for specific
formats, “radiotext” displays for station promos or advertising, personal
paging services, and “housekeeping” functions which enhance a
broadcaster’s service to his listeners.
The RDS data channel is transmitted as a low-level, double-sideband,
suppressed-carrier “subcarrier” at 57kHz, just above the spectrum of the
composite stereo program signal in the FM baseband. The data
transmission (baud) rate is modest, yet it is “robust,” thanks to data
redundancy and error correction.
The plug-in RDS Option for the Model 540 demodulates the 57kHz
subcarrier and reformats the RDS data stream into RS-232 serial digital
data which may be fed to any IBM-compatible computer. Supplied
software decodes the RDS data so that it may be read.
INSTALLING THE OPTIONAL PLUG-IN RDS CARD
If the Model 540 was supplied without the RDS Option, the rear-panel
RDS DATA OUT connector cutout will have been covered by a plastic
escutcheon. This may be removed, and the plug-in Option card installed
as follows.
First, remove two jackscrews from the DB-9 connector of the plug-in
Option card, and the spare 4-40 screw from the single threaded standoff
on the back of the board. Angle the Option card downward so that the
DB-9 connector pokes through the back-panel cutout. While gently
forcing the six Option connecting pins toward the back panel with your
thumb, align these pins with the mating connector strip on the main
circuit board and push the Option into its seated position. Re-install the
two jackscrews and the 4-40 screw to complete the installation.
COMPUTER REQUIREMENTS
RDS decoding and analysis software runs under DOS on any IBM-
compatible computer with a 286-or-better processor. The program will
run equally well on an old DOS machine, or under Windows®from the
MS-DOS Prompt command.
——
13
Connect the Model 540 to either the COM 1 or the COM 2 port of the
computer. Use a serial interface cable terminating in a DB-9 connector.
Cables with the larger DB-25 connectors will require a 9-to-25-pin
adapter on the end plugging into the Model 540.
INSTALLING THE SOFTWARE
Software is supplied on a 3½-inch floppy diskette. Since disk access time
is not a factor once the program is resident in computer RAM, it may be
run directly from the diskette if this is preferred. Most users will want
to copy the diskette to the computer’s hard drive. Two methods are
given here, choose whichever is more convenient.
DOS-Based
Computers Insert the diskette into the computer’s A drive. At the C:\>DOS
prompt, type: a: to access the diskette drive and bring-up an A:\>
prompt. At this new prompt type: install. This will create a C-drive
directory labeled 540RDS, and will copy all files from the diskette to
the hard drive.
Computers
Running
Windows®
Invoke the Run command under theStart utility. On theOpen line
type: a:\install. This will create a C-drive directory labeled 540RDS
and will copy all files from the diskette to the hard drive.
RUNNING THE DETECT PROGRAM
Starting the
Program
Under DOS
Two versions of theDETECT RDS-decode program have been included
in the 540RDS directory. The version you are most likely to use is for a
9600 baud data interchange rate. A second version supports 2400
baud, though the only reason to use this slower rate might be to
communicate with the Model 540 over a dial-up modem. For the 2400
baud rate a jumper must be changed on the RDS Decode Option plug-in
board (see Page 18).
From a C:\> DOS prompt, type cd 540rds to change to the proper
directory. Once the prompt has switched to C:\540RDS>, a properly
configured command line will start the program.
The command line must contain thenumber of the COM port which is
cabled to the Model 540, as well as thebaud rate for the RS-232 serial
data. For COM 1 the command line would be typed like this:
detect96 /1. For COM 2 type in: detect96 /2. (For 2400 baud
substitute the number 24 for the96 in either instance.)
Running Under
Windows®The DETECT program may be started under Windows®, simply by
“clicking” on theMS-DOS Prompt icon, then typing-in the command
line as described above. Users familiar with the Windows®operating
system can probably create a “shortcut” for click-starting the DETECT
program.
——
14
The DETECT
Screens The opening DETECT screen lists the functions which will be decoded,
and the RDS groups which contain this information. Press eto
bring up the main, data display screen. Pressing vwill exit the
program and return to a DOS prompt at any point.
The first line of the data display screen shows the station’s hexadecimal
PI Code (Program Identification), or “digital address.” This hex code
is automatically calculated from the station call letters in the RDS
encoding process. This is immediately followed by the Program Service
Name (PS) which can carry the station’s call letters or a “street name”
such as “LIVE 95” or “BIG 104.” The third item on this line is thePIN
(Program Item Number), an encoded schedule for a particular program,
its date and time.
The next line, PTY (Program Type) identifies the station format from
one of several pre-defined categories. TheTravel field indicates
whether or not the station is one which routinely broadcasts traffic
bulletins for motorists (TP), and indicates if such a message is
currently being broadcast (TA).
Two lines display the 64-character, plain-text Radio Text Messages
used for station promotions, contests or advertising. These messages
can be broadcast either in group 2Aor group 2B.
Alternative Frequencies (AF) is a list of all dial positions at which
identical programming can be heard. This will include the station’s
main transmitter and all “translators,” or re-broadcast facilities. The
list is displayed as received, and with a little practice you should be able
to catch all frequencies as they flash before you.
Audio Decoder Information identifies mono or stereo transmissions
(DI), and whether the program being broadcast is music or speech
(M/S).
MJD (Modified Julian Day) is a display of the current date and time. A
raw hexadecimal presentation is followed by the decoded day of the
week and date: day-month-year. The time display is current local time,
AM or PM, this is followed by an offset, in hours, from Coordinated
Universal Time (UTC). An offset of 7–would denote a local time 7
hours behind UTC, or that UTC is 7 hours ahead of local time.
The Enhanced Other Networks Data (EON) field gives some of the
same RDS features described above, but for program services separate
from the one being received. (Other stations in the same network with
their individual programming, for instance.)
Data Error
Display A digital counter at the bottom of theDETECT screen maintains a
running count of radiodata errors. The occasional “hit” is to be
expected, probably resultingfrom a noise burst or multipath effects.
Errors which appear to accumulate at a steady and regular rate,
particularly when signal strength is adequate, is a symptom of a
legitimate RDS data encoding problem and should be investigated.
——
15
Section V
CIRCUIT DESCRIPTIONS
This section details circuitry of the Inovonics Model 540 FM Subcarrier
Monitor/Demod, and also includes procedures for the comparatively few
calibration adjustments. Circuit descriptions refer to four pages of
Schematic Diagrams contained in the Appendix, Section V, Pages 25, 26,
27 and 28.
INTRODUCTION
Navigating the
Schematics Schematic component reference designations have not been assigned in
as haphazard a manner as they might at first appear. Instead of
annotating the schematics in a logical sequence, we have instead chosen
to designate thecomponents on the circuit board following their
physical placement, top-to-bottom, left-to-right. We expect this practice
will prove useful when troubleshooting, making it easier to locate the
physical part following analysis of the diagram.
The Model 540 schematic diagram consists of four sheets. Sheets 1 and
2 cover the main circuit board. Sheet 3 shows components on the
separate front-panel circuit assembly, and Sheet 4 is a diagram of the
optional RDS data-recovery plug-in module. Main-board components
begin with the number “1”; i.e.: R1, C1, IC1. Front-panel components
are in the five-hundred series; i.e.: R501, S501. Since it is a separate
circuit altogether, the RDS plug-in has its own, very short series of
numbers, again beginning R1, C1, etc.
The front-panel circuit assembly interconnects with the main board
with short ribbon-cable jumpers. J503 on the front-panel assembly
mates with J3 on the main board, J504 to J4, and J505 to J5.
The “PIC” and
Front-Panel
Logic
The Model 540 employs a device called a “PIC,” or Peripheral Interface
Controller. This is a single-chip microcontroller of limited intelligence,
but ideal for elementary logic and simple control functions. It is
factory-programmed to perform certain bonehead routines, most of
which deal with the front-panel buttons and indicators.
INPUT CONDITIONING AND FIRST TWO CONVERSIONS (Schematic Sheet 1)
Input Stage and
Band-Pass
Filter
The composite/MPX input from the station’s mod-monitor is adjusted
with INPUT LEVEL control R14 to calibrate the unit at full carrier
modulation. Buffer IC7A drives a high-pass L/C filter to attenuate
main-channel program frequencies below 50kHz, and following a
second buffer stage, IC7B, an L/C low-pass function attenuates out-of-
band noise above 100kHz. The selected band of frequencies is buffered
——
16
band noise above 100kHz. The selected band of frequencies is buffered
by IC8A which, along with companion inverting stage IC8B, provides
push-pull drive to the first balanced mixer, IC9.
Programmable
First LO Front-panel SUBCARRIER TUNINGbuttons S503 and S504 are read by
the PIC, IC6. A self-clocking up/down counter within the PIC controls
both the front-panel digital display, decoded by IC11 and IC17, and
tuning synthesizer controller IC5. The VCO section of phase-locked-
loop IC1 rounds-out the synthesizer circuit. The frequency range of
this first local oscillator extends from 401kHz to 356kHz, corresponding
to subcarrier frequencies between 54kHz and 99kHz, respectively.
Thus the first intermediate frequency is 455kHz, with an up-converted
spectrum inverted from that of the input signal.
First IF and
Second LO The 455kHz first IF is band-passed by the stagger-tuned, coupled-
transformer pair, T2 and T3. T3 feeds a second double-balanced mixer,
IC15. Local oscillator IC16 is crystal-controlled at 480kHz, down-
converting the tuned subcarrier to a second IF of 25kHz.
SECOND IF AND SCA DEMODULATION (Schematic Sheet 2)
Second IF Filter IC13A and IC12A constitute a four-pole low-pass filter, IC12B and
IC13B form a four-pole high-pass section. The resulting band-pass
function is theWIDE (SCA) characteristic of the front-panel FILTER
selector. This signal is presented to analog switch section IC28B to
select injection measurement bandwidth, also to the SCA demodulator,
and to yet another conversion process for further subcarrier selectivity
filtering.
SCA
Demodulator One section of hex inverter IC18A is biased into a quasi-linear
operating mode to afford broadband, open-loop gain. IC18B and IC18C
give additional amplification and pre-demodulation limiting of the
tuned subcarrier.
Differentiation and diode steering trigger IC18F on both the leading
and the trailing edges of the squared 25kHz IF waveform. Inverters
IC18D and IC18E complete a monostable (one-shot) multivibrator by
adding differentiated positive feedback through CR15. This yields a
string of fixed-width pulses, the 50kHz repetition rate of which is
frequency-modulated by SCA audio
IC25A and IC25B comprise a fifth-order, low-pass filter with a flat
frequency characteristic to just beyond 5kHz. This filter integrates the
string of 50kHz FM pulses, completing the demodulation process for
SCA audio program subcarriers.
De-Emphasis,
Audio Output
and Monitoring
150-microsecond de-emphasis is imparted by C76. Switch-selected
DE-
EMPH or FLAT SCA audio is switched by IC28A. The selected signal is
metered for theSCA AUDIO LEVEL measurement, and also routed to
IC26A and IC26B which deliver a balanced audio output to the rear-
panel connector.
——
17
panel BALANCED SCA AUDIO connector.
IC27A is a driver stage for the front-panel PHONES jack. This jack
monitors demodulated SCA audio in all measurement modes except the
CALIBRATE (±75kHz) position, in which IC28C instead routes de-
emphasized main-channel audio to the jack.
THIRD(!) CONVERSION (Schematic Sheet 2)
LO and Mixer The 25kHz IF signal is fed to a third mixer, IC30; the local oscillator for
this conversion is 25kHz from crystal oscillator/divider IC29.
Grammar-school arithmetic suggests a third IF frequency of either
50kHz or zero. The latter is actually the case. Politically-correct or not,
this “homodyne” technique allows a simple low-pass filter to establish
IF selectivity.
IF Filtering The third IF filter incorporates IC21B, IC21A and IC20A and has a 6-
pole low-pass function. IC19A compensates filter phase response, and
IC19B makes-up conversion loss. The effective IF bandwidth at this
point is about 3kHz. This third IF signal is useful only for injection-
level metering in theNARROW (DATA) position of the front-panel
FILTER selector. Down-converted essentially to DC at this point, the
signal is useless for further demodulation or audio monitoring.
METERING (Schematic Sheet 1)
Metering
Selector The front panel up/downMETER SELECT buttons are read by the PIC
microcontroller, which in turn sends a 2-bit binary address to a dual, 1-
of-4 analog switch, IC10. IC10A lights LEDs to indicate which scale and
metering function have been selected, IC10B routes the selected signal
to the metering rectifier.
In the 540’s CALIBRATE (±75kHz) mode, a composite/MPX sample from
input buffer IC7A is delivered to the meter. For subcarrier injection
measurements, both thePERCENT INJECTION and ±kHz DEVIATION
LEDs are lighted, and the input to the metering circuit is either the
WIDE (SCA)or the NARROW (DATA)IF signal from FILTER selector
IC28B. Calibrated, FLAT SCA program audio is fed to the meter for SCA
±kHz DEVIATION measurements, and for an indication of SCA AUDIO
LEVEL, either FLAT or DE-EMPH SCA program audio is delivered to the
metering circuit to be read on the lower dB scale. This level is factory
calibrated to read 0dB at ±5kHz SCA subcarrier deviation, but this may
be set to another reference value if desired. (See Page 20.)
Meter Rectifier
Gain stage IC22A feeds a full-wave, peak-responding rectifier using
IC23A, IC24A, IC24B and the four associated diodes. An input to the
meter immediately charges C66 to the instantaneous peak value.
Discharge of C66 is though constant-current source Q3. IC22B is a
slope detector which gives a positive output pulse whenever a new peak
exceeds the existing value. This pulse turns Q2 on, charging C65 which
——
18
exceeds the existing value. This pulse turns Q2 on, charging C65 which
holds Q3 off. C65 discharges through R78 and R80, ultimately enabling
current source Q3 and allowing a linear fallback of the bargraph
display. This action provides the peak-hold feature which makes even
the quickest deviations clearly visible.
Bargraph
Display The output of the metering rectifier is fed to a series of four bargraph
display drivers (Schematic Sheet 3), IC501 throughIC504, and hence
to the 38-segment LED readout. Q501 is turned on during subcarrier
injection measurements, this brings C502 into the circuit to reduce
display “bounce” from accompanying noise. Notwithstanding the
integration imposed by C502 and R509, the display remains peak-
responding due to the peak-hold provision of the rectifier.
RDS OPTION PLUG-IN ASSEMBLY (Schematic Sheet 4)
IC4 is an application-specific RDS decoder circuit originally developed
for receiver applications. It accepts the composite MPX signal directly
and performs on-chip signal filtering and data recovery. IC4 delivers two
logic-level outputs, clock and data, both derived from the incoming RDS
subcarrier.
Shift register IC3 converts RDS clock and serial data to an 8-bit parallel
format. This “scrolling” data “byte” is presented to a PIC
microcontroller, used in this instance as a sort-of “transmit-only UART”
(Universal Asynchronous Receiver/Transmitter). RDS clock pulses are
also fed to the PIC. Between these two input sources the PIC magically
sorts-out incoming data to yield a coherent output in RS-232 format.
Baud Rate
Jumper Data to the computer is available at two baud rates, these are selected
by a jumper on the RDS Option plug-in assembly. Though there is no
silk-screened legend on this little board, the baud rate is 9600 when the
jumper is closest to the DB-9 connector, and 2400 when it is moved
toward the AC mains connector. The factory setting is 9600 baud.
POWER SUPPLY (Schematic Sheet 2)
Model 540 circuitry utilizes ±9-volt supplies for op-amps and other
linear circuitry demanding signal headroom, and a +5-volt supply for
digital logic. These three sources are each regulated by a “3-terminal”
linear voltage regulator; IC2 for +9 volts, IC4 for –9 volts, and IC3 for +5
volts.
The power transformer has dual primary windings which may be
switched in parallel or in series to accommodate 115V or 230V mains,
respectively.
Table of contents
Other Inovonics Monitor manuals
