Marti R-15C User manual

WARNIN
II
THIS EQUIPMENT MUST BE OPERATED WITH A 3-PR
GROUNDED OUTLET RECEPTACLE. FAILURE
TO USE A
PROPERLY GROUNDED OUTLET MAY RESULT IN IMPRO-
PER OPERATION OR SAFETY HA
LIMITEDWARRANTY
The Seller warrants that, at the time of shipment, the
products manufactured by the Seller are free from
defects in material and workmanship. The Seller's
obligation under this warranty is limited to replace-
ment
or repair of such products which are returned to
Marti at its factory, transportation prepaid and
properly insured, provided:
a. Notice of
the claimed defect is given to Marti
within one (1) year [two (2) years for STL systems]
from date of original shipment and goods are returned
in accordance with
Marti instructions.
b. Equipment, accessories,
tubes and batteries not
manufactured by
Marti are subject to only such ad-
justments
as Marti may obtain from the supplier
thereof.
c. This warranty does not apply to equipment which
has been altered, improperly handled, or damaged in
any way.
The Seller is in no event liable for consequential
damages, installation cost or dher costs
of any nature
as a result of the use of the products manufactured or
supplied by the Seller, whether used in accordance
with instructions or not.
This warranty is in lieu of all others, either expressed
or implied. No representative is authorized
to assume
for the Seller any other liability in connection with
Seller's products.
MAILING & SHIPPING ADDRESS:
MARTI Electronics, Inc.
Cleburne,
Texas 76031 -0661
The United States of America
P.O. Box 661 1501
N. MainSt.
COPYRIGHT N
e1993 All Rights Reserved
Mad Electronics, lnc.
2nd printing, August 1993
No part of this manual may be reprodud,
transmitted, transcribed, stored in a retrieval
system,
or translated into any language, natural or comgater,
in any form or by any means, without the prior
written permission of
Marti Electronics, Inc.
Artwork depicting circuitry in this manual is
protected by copyrightlaws.
Information
in this manual is subject to change
without notice and does not represent
a commitmeat
on the part
of Marti Electronics, Inc.
Marti Electronics may make improvements andlor
changes in this manual or in the product
&scribed
herein at any time.
This product could include technical inaccuracies
or
typographical errors.
PHONE NUMBERS:
Sales & Service (81
7) 645-91 63
FAX [phone]
. . .. .

.
Introduction ......................................................................................................... : .............
Specifications ....................................................................................................................
Unpacking and Inspection .................................................................................................
Installation .........................................................................................................................
ElectricalConnections ......................................................................................................
STL System (Stereoand Mono) Block Diagram. No . 702-096 ........................................
Antennas ...........................................................................................................................
Operation ...........................................................................................................................
SystemPerformanceTests ................................................................................................
Theory of Operation ..........................................................................................................
Tools and Test Equipment Required .................................................................................
Frequency Selection(Programming Synthesizer.800-291) ...............................................
Adjustment LocationsDiagram, No . 702-099, R-15C .....................................................
Receiver Test Report .........................................................................................................
Tune-up and Adjustment ..................................................................................................
Block Diagram,No . 702-100. R-15C ...............................................................................
Main Frame
0
1st Converter
890-960MHz
.
1st Converter
280-480MHz
.
1 s t Converter
140-260MHz
.
Frequency Synthe-
sizerBoard
2nd Converter/
IF
Amplifier/ Detector
IF Bandpass Filter
Audio Board
Meter Board
c
Power Supply/
SquelchBoard
Y
Schematic.702-095 .........................................................
Parts List. 702-095 ..........................................................
Schematic.800-211B ......................................................
Parts List. 800-211B ........................................................
Schematic.800-213 .........................................................
Parts List. 800-2 13 ..........................................................
Schematic.800-212 .........................................................
Parts List. 800-212 ..........................................................
Schematic.800-291 .........................................................
Parts List. 800-291 ..........................................................
Schematic. 800-293 .........................................................
Parts List. 800-293 ..........................................................
Schematic. 800-207-250 .................................................
Parts List. 800-207-250 ..................................................
Schematic. 800-294 .........................................................
Parts List. 800-294 ..........................................................
Schematic.800-295 .........................................................
Parts List. 800-295 ..........................................................
Schematic. 800-219A ......................................................
Parts List. 800-219A .......................................................
1
2
4
5
5
7
8
10
12
14
16
17
18
19
25
26
28
29
30
31
34
35
42
43
48
49
52
53
56
57
58
59
64
65
66
67
i

InpuVOutput Filter Schematic, 800-193A ...................................................... 69
Board Parts List, 800-193A ....................................................... 70
-7
.
ii

Introduction
1
1 I
The Marti STL-15C Transmitter with companion R-15C Receiver, form a high quality, fre-
quency synthesized, point-to-point, line
of sight, radio communications link. These systems are
available in frequency bands from 140 MHz to 960 MHz and may be factory configured for op-
eration from various power sources. Depending upon available channel bandwidth, these systems
can transmit
one of the following:
c
Composite FM Stereo audio with two ~ubcarrriers*
Monophonicaudio with two subcarriers
Digitalstereo audio (requires external modems)
0 Multi-channel audio or duta (requires external MUX)
Digitaldata (requires external modems)
Complex systemscan be built from basic STL-15C transmitters and R-15C receivers having mul-
tiple relay (repeaters), bi-directional (full duplex), and automatic switching hot standby features.
I Compositesystem specifications I
Stereo separation:
55 dB orbetter 50 Hz - 15 KHz with 250 KHz IF Filter
50 dB with 200 KHz IF Filter
0
Frequency response:
Composite channel d.2 dB 30 Hz - 53 KHz
Wide band channel a.3 dB 30 Hz - 100 KHz
c
1

Distortion: 0.2% or less 30 Hz - 15 KHz
LPfiltered left
or right channel)
emphasized,LP filtered left or right channel)
Emission: 194 KF8E (without subcarrier)
280 KF8E (with
1 subcarrier)
490 KF8E (with 2 subcarriers)
(demodulated, de-emphasized,
Noise: more than 72 dB below 100% modulation (demodulated, de-
* 940 - 960 MHz system, 500 KHz channels. Narrower bandwidths at reduced specifications.
1 Monophonic system specifications
Frequency response: k0.25 dB
30 Hz - 15 KHz
Distortion: 0.2% or less 30 Hz - 15 KHz
Noise: more than 72 dB below 100% modulation (75 ps de-emphasis)
Emission: 194 KF8E (mono channel with subcarrier)
Pre-emphasis Adjustable 0,25,50, or 75 microseconds
.
Model R45C
Aural STL Receiver
Specifications
Frequency range: 140 - 180 MHz R- 15C/150
R- 15C/215
R- 15C/300
R- 15C/450
R- 15C/950
200
- 260 MHz
280
- 340 MHz
400 - 480 MHz
890 - 960 MHz
2

Sensitivity:
RF Input Impedance
and Connector:
Selectivity:
SpuriousResponse:
Frequency Stability:
Frequency Synthesizer:
MonophonicAudio
.
output:
Composite Audio
output:
SubcarrierOutputs:
Digital Output:
Front Panel Controls:
Composite stereo demodulated,de-emphasized, LPfiltered, or
monaural
3 microvolts input for 50 dB signal/noiseratio
9 microvolts input for 60dB signalhoiseratio
75 microvolts input for ultimate signal/noise ratio (typically 75
dB or better
50 ohms, type UG-58 (N female)
IF filter bandwidth is determined by the subcarrier(s) on the
system and interference conditions. Minimum necessary
bandwidth is selected from options:
Filter
3 dB 60 dB (bandwidth, KHz)
F200 190 450
F250 220 530
F450 280 900
-90 dB, 140-480MHz;
-70 dB, 890-960MHz
k .00025%, -20°C to +50°C
Frequency selected by 16DIP switches,maximumresolution
12.5KHz
Balanced 600ohms, level adjustable
-30 dBm to +10 dBm at
front panel, transformer isolated and floating (may be strapped
for transformerless output)barrier strip terminals. Response
30
HZ - 15 KHZ k 0.25 dB.
Level adjustable 1.8v
P-P to 3.5 v P-P at front panel,
unbalanced BNC connector;composite frequency response
30
HZ - 53 KHZ k0.2 dB.
Two unbalanced outputs,BNC connectors, selectable high pass
filtering for monophonic or composite stereo modes. Subcarrier
output levels are 2
- 3 v. P-P for 10% subcarrier insertion at the
STL-15Ctransmitter. Subcarrierhigh pass filter cut-off
frequency is 25
KHz in “mono mode” and 80 KHz in
“composite mode.”
The 52 “Composite Output”BNC connector can be converted
to
a “Digital” output by connecting an alternate shielded wire
by changing two pins in
a cable connector.The “Digital”
output is unfiltered, unprocessed baseband having a
3 v. P-P
level and a response of 30 Hz - 200 KHz.
10 dB Attenuator, CompositeLevel Adjust, Mono Level
Adjust, Squelch Adjust, and Meter Switch.
a
3

Metering and
Indicators:
Automatic Changeover
:
Accessory connector:
PowerRequirements:
AC Fuse Rating:
Dimensions:
Weight:
Test meter
reads Signal Level, ProgramLevel (mono or
composite),
SubcarrierLevel, AFCLevel, Local Oscillator
Level,
and Mixer Level. LED's indicate AFC Lock,
CompositeMode, Mono Mode,
and SquelchOpen.
Provision for automatic changeover by addition of ARS-2
Automatic Receiver Switcher.
15pin D connector on rear panel provides filtered access to
+13.5 v regulated bus, +18 v unregulated supply, Squelch
relay contacts.
120/220/240VAC*, 50/60 Hz, 20 watts or 11 - 14 VDC
negative ground
or 22 - 28 VDC** negative ground at 600 ma.
(900 ma. initial warmup.
For 120v. use
0.5 Amp fuse
For 220 v. use 0.25 Amp fuse
3.5 inches High x 19inches Wide x 13inches Deep
8.89cm High
x 48.26 cm Wide x 33.02cmDeep
Net
9 pounds. Domestic packed 13pounds.
Net 4.1 kilograms. Export packed 5.9kilograms.
* Voltage must be specifiedwith order.
** Requires APS-28/18PowerSupply.
Specificationssubject
to change without notice
This equipment was factory tested, inspected, packed, and delivered to the
carrier with utmost care.
Do not accept shipment from carrier which shows
damage
or shortage until the carrier's agent endorses a statement of the
irregularityonthe faceof the carrier's receipt.Without documentaryevidence, a
claimcannot befiled.
Unpack equipment immediately upon receipt and thoroughly inspect for
concealed damage.
If damage is discovered, stop further unpacking and
request immediate inspection by localagent of carrier.
A written report of the
agent's findings, with his signature
is necessary to support claim. Check your
shipment against the shipping papers
for possibleshortage. Do not discard any
packingmaterial untilall items are accountedfor. Small items are often thrown
away with packing material. Packing material should be retained until
equipment testing
is completed. Any equipment returnedto the factory should
bepackedinoriginalcartons, insured, andpre-paid.
4

I /nsta//ation
Frequency
Install rack-mounted equipment in
a well-ventilated, well-grounded, and
shielded rack cabinet.
Do not locate
solid-state equipment
in a rack above
tube-type equipment which produces
hightemperatures.
Problems can also be avoided by
locating
this unit away from other
equipment which has transformers
that produce strong magnetic fields.
These fields can induce hum and
noise into the Marti equipment
thus
reducing performance. Strong radio-
frequency
(RF) fields should be
avoided where possible. Extensive
shielding and filtering have been
incorporated into
this equipment to
permit operation
in moderate RF
environments. All equipment racks,
cabinets, etc., should be bonded
together
by wide copper grounding
strap to ensure that all system
elements areat
RF ground potential.
Bandwidth (3dB)
Receiverconnectionsfor
Composite Stereo operation
(Refer to Drawing 702-096)
1. The composite signal output of the R-15C
Receiver is
the BNC jack labeled “52
COMPOSITE”.
The composite output is connected
to the composite signal input of the FM transmitter
exciter by
a shortlength of RAG-58 coaxial cable.
2. A subcarrier demodulator or remote control
(operating above
92 KHz) can be connected to “J1
SUBCARRIER NO. 1”
and/or “J3 SUBCARRIER
NO.
2” output BNCjack. The ability of the STL-ISC
system to transmit subcarriers depends upon
the
channel bandwidth available. The R-15C receiver IF
filter selectivity must be compatible with the available
interference free channel bandwidth. Using
50 KHz
deviation for 100% modulation, the approximate
bandwidth required for various subcarriers follows:
92 KHz
110 KHz
180 KHz
I Subcarrier I Receiver IF I
284 KHz
320 KHz
460 KHz
Actual bandwidth may require an additional 10%
to 15% to allow for the modulation on the subcarrier
itself. With the severe
STL channel crowding with
resulting interference prevalent around large markets,
subcarriers above
110 KHz are not recommended.
3. The accessory connector has several uses such as
remote control, automatic switching,and external DC
power. Connection instructions are furnished with
these accessories.
4. Connect STL receiving antenna coax to “56
ANTENNA”.
This requires a type N male connector.
A short flexible jumper (20” max.) may be used
between
J6 and semi-flexible coax. Marti Part No.
585-017
double shielded, low-loss RG 214/U jumper
is recommended.
5. Connect AC line receptacle on back of the
receiver to a I15 volt AC power source with special
cord set supplied.
USE ONLY 3-PRONG
GROUNDED OUTLET RECEPTACLES FOR
SAFETY.
WARNING
This equipment must be operated
with
a 3-prong, grounded, 11 5 volt,
AC outlet receptacle! Failure to use
a properly grounded outlet could
result in a safety hazard or faulty
equipment performance!
(See nextpagefor receiverconnections for
monophonicoperation.)
5

R-lX Receiver connections
for Monophonicoperation
(Refer to Drawing 702-096)
1. Monophonic program audio output is available at
“600 ohm balanced” audio output screw terminals,
TB-1. Use shielded wire. Program audio output level
is
+IO dBm max, 600 ohms balanced, and isolated
from ground.
For dual channel stereo, repeat
instructions at second receiver. Audio processing
requirements will be discussed
in the “OPERATION’
section of this manual.
2. Connect a remote control
or subcarrier
demodulator to the jack marked,
“51”. The
subcarrier load may be 600 to
5K ohms impedance,
and the output level is approximately one
(1) volt
RMS. Systems factory supplied with 250 KHz IF
bandwidth will carry subcarriers up to
92 KHz. For
other subcarrier frequencies
or narrow IF bandwidth
systems contact the factory. A second subcarrier
system can be connected to
“53”. If a dual channel
stereo
STL is used, connect one subcarrier generator
to
“51” or “53” on each channel’s transmitter and
receiver.
3. The accessory connector has several uses such as
automatic switching, and external DC power.
Connection instructions are furnished with these
accessories.
4. Connect STL receiving antenna coax to, 56
ANTENNA. This requires a type N male connector.
A
short flexible jumper (20” max.) may be used
between
56 and semi-flexible coax. Marti Part No.
585-017 double shielded, low-loss RG-2 14/U jumper
is recommended.
5. For dual channel stereo, use Model MTS-1
Receiver Combiner
between 56 of each receiver.
Use
a Part No. 585-017 jumper between the
ANTENNA connector of the MTS-1 and the semi-
rigid coax. Refer
to Drawing 702-096.
6. Connect AC line receptacle on back of the
receiver to a
115 volt AC power source with special
cord set supplied.
USE ONLY 3-PRONG
GROUNDED OUTLET RECEPTACLES FOR
SAFETY.
WARNING
This equipment must be operated
with a 3=prong,grounded, 11 5 volt,
AC outlet receptacle! Failure to use
a properly grounded outlet could
result in
a safety hazard or faulty
II equipment oerformance! II
.
I
6

.
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7

IAntennas
The following suggestions are offered to
help those responsible for antenna installa-
tions avoid costly errors in assembly and
adjustment. Marti Electronics, Inc. assumes
no responsibility for the installation and
performance of antenna systems associated
with its equipment. The following sugges-
tions are not intended
to be a complete step-
by-step procedure, simply a listing of some
of the most frequently reported errors in an-
tenna system installation.
Antenna Assembly
Follow the manufacturer’s instructions carefully.
If
no instructions were included with the antenna, call
or write the antenna manufacturer for instructions.
Errors are frequently made in assembly of the RF
feed dipole in multi-element grid parabola antennas.
The feed dipole elements must be installed
in the
same plane
as the reflector grids. In other words, if
the reflector grid elements are horizontal. the feed
dipole elements must
also be horizontal. Cross
polarization of grid and feed dipole will result
in total
loss
of antennagain!
Transmission Line Connector Assembly
Do not use RG-58 U or RG-8 U cable with anten-
nas! They have too much loss at VHF and UHF
frequencies. Use low-loss foam dielectric solid
copper outer shielded and jacketed coaxial cable of
1/2” to 1-5/8” diameter. Follow the instructions
furnished by the manufacturer when cutting coaxial
cable. Inspect
the cable ends for small metal frag-
ments which can short-circuit the line inside the
connector assembly. Check
the line for a short-circuit
condition after each connector is installed by using an
ohmmeter.
Moisture ProofingCoax Connectors
Extreme care must be exercised with coaxial cable
before and after connectors have been installed to
ensure that moisture does not enter
the line. Foam
dielectric line can take on moisture absorption which
is difficult
to detect and remedy. Therefore. keep the
line dry while in storage with ends tightly capped.
Coaxial splices, connectors. and fittings, to be located
outside should be made mechanically tight.
then
coated with a weather-proofing material over at least
two layers of vinyl plastic electrical tape. Moisture
problems
in antenna systems are usually traced back
to connectors which have NOT been properly taped.
The Marti K-1 Grounding and Weatherproofing Kit
is
recommended for use in each new antenna
installation.
Locationand Grounding of Coaxial
Cable
Keep the STL receiver coaxial cable as far from
the broadcast transmitter and its coaxial cable as pos-
sible.
DO NOT STRAP RECEIVER CABLE TO
THE MAIN ANTENNA CABLE AT
ANY POINT.
PLACE THE RECEIVER ANTENNA COAXIAL
CABLE ON THE OPPOSITE SIDE
OF THE
TOWER FROM THE MAIN ANTENNA
CABLE.
Maintain maximum separation between these cables
at
all points, including the distance from tower base
to transmitter building
as well as inside the building.
System Grounding
It essential that the STL antenna system be prop-
erly grounded for safety and proper operation.
Antenna Installation andAdjustment
The polarization of the transmit and receive anten-
nas of the STL system must be the same! This means
that
if the transmitting antenna is vertical, the
receiving antenna must also be vertical. Each antenna
should be attached to the tower using the proper side
mount
or top mount hardware. Each antenna should
be attached
to the tower to allow for final adjustment
in azimuth heading and vertical tilt. After visual
adjustment
of the antennas, the transmitter and
receiver can be used to make the final adjustments of
the antennas. With the transmitter driving one
antenna,
the receiving antenna is adjusted for
maximum signal (indicated on
the receiver) in both
horizontal and vertical directivity. CAUTION:
Antennas have a ”major” and several “minor” lobes
in their directivity patterns. A common error is to
peak
the antenna on a minor lobe, resulting in a signal
level of only
a fraction of the major lobe signal. This
error can be avoided
only by swinging the antenna
through a large angle
so that all lobes are evaluated
and the major lobe clearly determined. After one
antenna is adjusted, the transmitter and receiver
locations are reversed, to allow adjustment of
the
other antenna. If an RF watt meter is available, each
antenna and transmission
line can be checked for
.

VSWR when the transmitter is supplying power to it.
The VSWR should be less than 1.5 to 1 (1.5: 1).
.
LEVEL, THE FOLLOWING ITEMS SHOULD
1. Check for correct assembly of antenna. Grid
reflector antennas must have the drive dipole
parallel with reflector grid bars.
2. Check that antennashave same polarity.
3. Check orientation of antennasin both
horizontal and vertical directions.
4. Check VSWR of both transmit and receive
antennas.
VSWR should be less than 1.5:l.
5. Check Fresnel zone clearance along radio
path.
6. Check for obstructionsin the path such
as trees and man-made structures. Thebase
antenna must be high enough to provide a
line-of-sightpath to the remote transmitting
antenna.
9

Control Functions and
Panel Indicator Lamps
COMPOSITE LEVEL
When selected by internal jumper plugs, the
“COMPOSITE LEVEL” lamp will be illuminated.
Composite output is adjustable over a range of
1.8 to
3.5 volts P-P.
-3.5 vu
-I vu
0 vu
MONO LEVEL
When selected by internal jumper plugs, the
“MONO LEVEL” lamp will be illuminated.
Balanced
600 ohm mono level is adjustable over a
range of
-40 to +IO dBm.
max sensitivity
IO
max sensitivity 100
max sensitivity 50
SQUELCH ADJUST
The SQUELCH ADJUST pot is used to set the
minimum level of received signal required
to ”open”
the audio squelch of
the receiver. This level is factory
set to
4 microvolts, but may be changed if necessary.
The squelch should be set to open when receiving the
signal from the
STL- 15C transmitter, and close and
remain closed at all times when
the transmitter is
“OFF”. Very sensitive (low level) settings should be
avoided to prevent the squelch from opening
on noise
or other signals.
ATTENUATOR
The RF input sensitivity of the R-15Creceiver can
be attenuated by placing
the “ATTENUATOR”
switch in “10 dB A’ITEN.” position. This may be
desirable when the received signal is very strong in
order to bring the “SIC. LEVEL“ meter indication on
scaleand
to make the squelch relay less susceptible to
noise and interfering signals. On long transmission
paths and fading signal conditions.
“MAX
SENSITIVITY” setting is required.
AFC LOCK LIGHT
The AFC LOCK light should be illuminated at all
times
the receiver is operating. This indicates the
VCO of
the frequency synthesizer is locked to the
reference oscillator.
The receiver squelch relay will
not open unless the
AFC LOCK light is on.
Test Meter
An illuminated TEST METER and selector
switch are built into
the R-15C receiver to permit
monitoring
of critical parameters. These are:
1. “SIGNAL LEVEL” - The received signal
strength indication (RSSI) is displayed in relative
values on
the “VU’ scale of the meter when switched
to “SIC. LEVEL”. Typical RSSI values and
conditions are shown in the following table:
Sig. Level Signal
Meter Attenuator Strength
max sensitivit
+1.5 VU
1 max sensitivity J 250
0 vu
1 10dBATTEN I 500
See Receiver Test Report on page 17
2. “PGM LEVEL” - The recovered audio level
(mono or composite) is displayed on the upper “VU’
scale of the meter. This indication may be useful in
initial set-up under test tone conditions. “Composite”
or “mono” levels may be observed while adjustments
are being made. The program level meter
is not a
peak reading meter and is useful for test tone
measurements. Complex program audio will be
indicated at about
6 dB below actual peak values. The
modulation of the
STL link is set at the “PEAK
MODULATION” bar graph meter of the STL-I5C
transmitter. “Composite” or “mono” levels out of the
R-15C receiver are
set for correct modulation of the
broadcast transmitter as indicated
on the station’s
modulation monitor.
3. “SUB LEVEL” - Received subcarrier level is
indicated
in this switch position. If 10% subcarrier
injection is used at the
STL- 15C transmitter. a “SUB
LEVEL” indication of approximately “0‘’ VU is
indicated.
3. “AFC LEVEL” - Inulcates the AFC error
correction voltage
in the phase-locked loop. This
reading should be
“0 VU” -CIS VU. Level errors
greater than
f1.5 VU call for adjustment of VCO
center freauencv. Seesection:
10

5. “L. 0. LEVEL” - The local oscillator (L.O.)
level meter reading is normally -5 VUto -3 VU.
6.
“MIXER” - The mixer meter reading is normally
- 3 vu to +3 vu.
I
It is prudent to recordall meter read-
ings at the time the equipment is
initiallyinstalled
to aid infuture
trouble shootincr.
INTERNALLY SELECTED
OPTIONS
The R-15C receiver has several options selected
1 FREQUENCY PROGRAMMING
The R-15C receiver frequency synthesizer is
programmed by 16 switches located on the
R-15C
Frequency Synthesizer Board, 800-291. Refer to
section titled:
11

ce
The STL-15C transmitter, R-15 receiver with the
associated antenna system can be tested and com-
pared with factory test data included
in this manual.
The followingprocedures should be followed
in order
to obtain reliable and accurate results.
Before audio tests
or subcarrier tests are begun check
the receiver
“SIG. LEVEL” METER for required
minimum signal. A conversion from
VU to micro-
volts
is given under OPERATION in the R-15 re-
ceiver manual.
For a 950 MHz. system using 50 KHz
FM deviation, typical noise levels are:
1 pv for 20 dB SM ratio
3 pv for 50 dB SM ratio
IO pv for 60 dB SM ratio
20 pv for 70 dB SM ratio
50-1-pv for ULTIMATE
(Demodulated left
or right channel de-em-
phasized and low-pass filtered.)
For the above system with 20% subcarrier injection,
the following noise level on the subcarrier (Marti
SCG-IO
- SCD-IO System) was measured: (no
modulation main
or sub)
10 pv for 40 dB Subcarrier S/N ratio
20 pv for 47 dB Subcarrier S/N ratio
30 pv for 50 dB Subcarrier S/N ratio
150 pv for ULTIMATE
With ultimate
S/N ratio, main to sub crosstalk should
be
-40 to -45 dB (using Marti SCG-10 - SCD-10
Subcarrier System).
(monophonic mode)
Noise measurements should be made first. since high
noise levels will influence distortion readings. Also
ground loops
in the audio oscillator to transmitter
12
connections and distortion analyzer to receiver con-
nections must be resolved before testing begins. The
influence
of high RF fields upon the test equipment
must be determined and corrected before accurate
measurements can be made. NOTE: NOISE AND
DISTORTION MEASUREMENTS ARE MADE
WITH SUBCARRIER AND REMOTE CONTROL
INPUT SIGNALS REMOVED. System signal to
noise ratio
is determined while modulating the
transmitter
100% at 400 Hz. A level of +8 dBm
across the balanced audio input terminals of TB-
1
will produce a reading of 100% modulation on the
“PEAK MODULATION’ indicator. Set Receiver
“MONO LEVEL” pot for
+IO dBm output into the
distortion analyzer. If the distortion analyzer has a
high impedance input, add a
600 ohm load resistor to
match the receiver. Establish
+10 dBm on the audio
voltmeter of the analyzer
as the reference level for
100% modulation. Next, remove the audio signal
from the transmitter input and measure noise level
below reference (100% modulation). This reading
should compare with that published under
SYSTEM
SPECIFICATIONS in this manual.
DlSTO RTlO N
(monophonic mode)
Harmonic distortion is usually measured at 100%
modulation and at several frequencies. If pre-em-
phasis processing is used
in the transmitter with cor-
responding de-emphasis
in the receiver, it is normal
for available audio level at
the receiver to drop with
increasing frequency according to the de-emphasis
curve selected. At
15 KHz, there is sufficient level to
operate most modern distortion analyzers. Distortion
levels should
be within specifications. If distortion is
out of specs, check system noise, check for test
equipment ground loops,
RFI, and transmit-
terheceiver operating frequency. If either
unit is off
frequency, the
FM modulation sidebands are not
centered within the
IF filter bandpass, which can
cause audio distortion.
FREQUENCY RESPONSE
(monophonic mode)
If the STL-I5C System is switched to flat processing,
frequency response can be measured
as if the signal
were being sent over straight wires. If pre-emphasis
processing is used (especially
75 ps) allowance must
,

be made in the transmitter audio input level to pre-
vent over-modulation at test frequencies above
400
Hz. The simplest and fastest method is to set the
transmitter audio input level for 100% modulation at
400 Hz., then attenuate this level 20 dB. Set receiver
output level to -10 dBm
as the reference. then sweep
the audio band for response. Response should be
within
SYSTEM SPECIFICATIONS.
COMPOSITE (STEREO) SEP-
A RAT1 0 N, NOISE, DlSTORTlON
AND FREQUENCY RESPONSE.
(composite mode)
This procedure consists of feeding a stereo encoder
(generator) capable of more than
60 dB separation
(50 Hz - 15 KHz) into the composite input of the
STL- 15C transmitter and connecting a stereo decoder
(monitor) to the composite output
of the R- 15C
receiver. The actual test procedure may vary with
different decoders (monitors). Therefore the proce-
dure prescribed
in the decoder (monitor) instruction
manual should be followed.
13

The Marti R-15C is a synthesized double-
conversion superheterodyne receiver. When used
with the companion STL-15C transmitter a high
quality point-to-point radio link can be assembled
for transmission of composite stereo audio,
monophonic
.iudio, digital data (by means of
modems) or other communications.
Since the general theory of operation of
superheterodyne receivers
is well known, we will
briefly describe the function of each board
(subsystem)
of the R-15C receiver. Refer to block
diagram 702-100 for signal
flow, and to the
individualschematicdiagramsfor circuitdetails.
1 st CONVERTER, 800-21 1
800-212, 800-21 3
The received RF signal is applied to the 1st
converter module. After passing through
a three-
section preselector, the signal is coupled to Gate
No.
1 of a GaAs dual-gate RF amplifier. The output of
this amplifier is impedance matched to Double-
Balanced Mixer
X-I. The output of the Local
Oscillator frequency multipliers is
also impedance
matched to the local oscillator port of mixer
X-I. The
third port of the double-balanced mixer
X-I is the
converter output. The 1st converter output is in the 70
- 78 MHz range.
SECOND CONVERTER / IF
AMP / DETECTOR, 800-293
The 50 ohm output from the 1st converter is
connected to J3 of this board by a short coaxial cable.
J-FET Q4 raises the impedance for
the two-section
band pass filter which
is tuned to the 70 - 78 MHz
output of the first converter. This signal is amplified
by dual-gate
FET Q5, again filtered by L7K.18 then
fed to the gate of Q6. J-FET
46 is a source follower
driving the 50 ohm
RF input of double balanced
mixer
X 1. The L.O. drive from Synthesizer Board,
800-291,
is connected to the L.O. port of mixer X1
via connector J5. The 10.7 MHz frequency difference
between the
RF and L.O. signals appear atthe IF port
of mixer
XI which is connected to J4. The 10.7 MHz
signal is routed through
IF Bandpass Filter Board,
800-207,
and back to J1 of Second ConverterDF
Amp/ Detector Board,
800-293, for amplification by
QI and Q2 with filtering by CFI and CF2. IC5
combines the functions of IF amplifier/limiter,
quadrature detector, and receive signal strength
indicator (signal
level metering). The wide band
output of Q5 appears at Pin 6, and is connected to
IC1
- IC4 for pre-processing of the composite, mono,
and subcarrier signals, and for
level metering.
AUDIO BOARD, 800-294
Audio Board, 800-294 processes composite and
mono audio for the R-15C and is programmable (by
jumper plugs) for composite stereo
or monaural
signal processing.
Using “jumper plugs” the user may select *‘HI-
SUB” for subcarrier operation in Composite mode or
“LO-SUB” for subcarrier operation in mono mode.
When changing mode
of operation jumper plugs are
also provided to switch
the front panel LED mode
indicators and level metering.
See the NOTE on
Schematic,800-294 to setjumpers properly!
COMPOSITEPROCESSING:
Composite processing entails low pass filtering,
delay equalization, and high pass
filtering (for
subcarriers). Low pass filtering achieves a flat
amplitude response
to 53 KHz with a “brick-wall”
cut-off using elliptic filters. Group delay, introduced
by the low pass filter, is equalized using active
all-
pass filters and achieves a flat group delay across a
frequency band of 50 Hz to 53 KHz. High pass
filtering, using elliptic filters, has
a “brick-wall” cut-
off at 80
KHz. with a flat response beyond 80 KHz.
The output, as indicated on schematic 800-294, is
labeled “HI-SUB”.
MONO PROCESSING:
Mono processing entails de-emphasis, low pass
filtering, amplification, and high pass filtering (for
subcarriers).User options provide for selection of 75
ps, 50 us, 25 ps, or 0 ps de-emphasis. Active
Butterworth low pass filtering achieves a flat
amplitude response
to 15 KHz rolling off sharply
above
15 KHz. Active Butterworth high pass filtering
provides a sharp roll-off at 25
KHz with tlat
amplitude response above
25 KHz for subcarriers.
14

Output of the high pass filters is labeled “LO-SUB’’
on Schematic, 800-294. See instructions on this
schematic for selection of “mode”, de-emphasis,and
subcarrier
FREQUENCY SYNTHE-
SIZER, 800-291
The R-15C receiver frequency is synthesized at
the second conversion local oscillator frequency,
which is 10.7 MHz below (or above) the first
converter output frequency. Using the 944
- 952 MHz
band
as an example, the first converter output would
be
70 - 78 MHz. To convert to the second IF
frequency of 10.7 MHz, the synthesizer must generate
the required frequency
in the range of 59.30 to 67.30
MHz (F-10.7) or 80.70 to 88.70 MHz (F+10.7).
Programming instructions for the synthesizerare
on page
19.
The frequency synthesizer consists of a Phase-
Locked Loop (IC5), a Voltage-ControlledOscillator
(Q2),
a Pre-scaler (IC4), a ReferenceFrequency (Y l),
and a Loop Filter (IC2A). The PLL is a
programmable device with the reference frequency
generated by a crystal oscillator. The loop filter is an
active type and the pre-scaler is used to pre-scale the
VCO frequency to make
it compatible to the PLL.
The PLL performsthree major functions:
I. compares the phase of the pre-scaled VCO
frequency (further processed inside the device)
with the frequencyof resolution and produces
outputs that are used by the loop filter to produce
a
DC voltageto control the VCO frequency.
.
.
2. controls the pre-scaler by selecting its divisor.
3. generates the frequency
of resolution,
internally, using the crystal oscillator.
The PLL has 16 programming pins that are used
to select
a VCO frequency and produce a lock. The
program to select a particular VCO frequency is
selected by
16 dip switches. An extremely stable
crystal oscillator and noiseless loop filter make the
synthesizer ultra stable. The output of the phase-
locked VCO (Q2) is buffered by IC3,
low pass
filtered and connected to J1 (L.O. out). A short
coaxial cable connects with J5 (L.O. in) of Board,
800-293.
INPUTOUTPUT FILTERS,
800-193A
All inputloutput circuits connected to
ACCESSORY connector J4, as well as the AC line
input, have radio-frequencyfilters.
POWER SUPPLY/
SQUELCH,800-219A
The power supply consists of a bridge rectifier,
D1, D2, D3, D4 filter C5 and regulator IC-3. R8 and
R9 set the output voltage and D5 and D6 protect IC-3
from reverse voltage. Zener diode D7 provides a
shunt regulated reference voltage for the comparators,
IC-2, for instances when the receiver is operated from
external unregulated DC supplies.
The signal squelch
IC-2B comparator has the
signal level metering voltage applied to the
appropriate input. Signal squelch comparator IC-2B
output is connected to relay driver 42. The collector
of Q2
also operates the “SQUELCH OPEN’ LED on
the receiver panel. Squelch adjustment is provided by
potentiometer R1 located on METEWCONTROL
BOARD, 800-295 which divides the comparator
reference voltage through R11 and R12.
The signal level voltage is inhibited (shorted
to
ground) when the frequency synthesizer AFC LOCK
light is
NOT “ON’, thus muting all receiver signal
outputs.
Signal level voltage is also connected to meter
driver amplifier IC-
1. The “SIGNAL LEVEL”
position of the test meter is calibrated by R2.
15

Distortion Analyzer
Oscillator
Attenuator Set
Frequency Counter
Digital Multimeter
AnalogMultimeter
RF Attenuator
RF Signal Generator
Stereo Monitor
Stereo Generator
Oscilloscope
Krohn-Hite Model 6801
Krohn-Hite Model4500
Hewlett-Packard Model 3500
Hewlett-Packard Model 5383A
(option
001)
Beckman Model 3030
Triplett Model 630
Kay Model437A (adjustable 0-1
10 dB)
Marconi Model 2022C
Belar ModelFMS-2
Aphex Model
AX400
Tektronix Model 2215
I TypeofTooi I Manufacturer’s No. I Marti Part No. 1
Tuning Tool GC 9300 930-037
Tuning Tool
GC 9440 930-069
Tuning Tool Spectrol 8T000 930-100
Tuning
Tool Sprague-Goodman 930-062
Tuning Tool Johanson 8762 930-096 (yellow)
Tuning Tool Johanson 8766 930-076 (blue)
The
STL-lSC/R-lSCAlignment Tool Kit (Marti Part No. 704-175) containing all the
above tools may be obtained from the factory for $19.83.
16