Marti Electronics STL-10A User manual

MARTI
ELECTRONICS
STL TRANSMITTER
MODEL STL–10A
October, 2001 597–9500

i
TECHNICAL MANUAL
MARTI ELECTRONICS
STL-10A BROADCAST STL TRANSMITTER
TABLE OF CONTENTS
DESCRIPTION PAGE NO.
INTRODUCTION – STL–10A 1
SPECIFICATIONS 3
UNPACKING AND INSPECTING 5
INSTALLATION 5
STL–10A TRANSMITTER INSTALLATION 5
ANTENNA INSTALLATION 6
STL ANTENNA INSTALLATION CHECKLIST 6
ANTENNA ASSEMBLY 6
TRANSMISSION LINE CONNECTOR ASSEMBLY 6
MOISTURE PROOFING COAX CONNECTORS AND FITTINGS 6
LOCATION AND GROUNDING OF COAXIAL CABLE 7
SYSTEM GROUNDING 7
ANTENNA INSTALLATION AND ADJUSTMENT 7
OPERATION 7
SWITCH AND METER FUNCTIONS 7
TRANSMIT–OFF SWITCH AND LED 7
FORWARD–REFLECTED SWITCH AND RF POWER METER 8
PEAK MODULATION METER 8
TEST METER 8
PRE–EMPHASIS SWITCHES 9
FREQUENCY MEASUREMENT 9
STL–10A PERFORMANCE TESTS 9
NOISE 10
DISTORTION 10
FREQUENCY RESPONSE 10
STL–10A THEORY OF OPERATION 10
POWER SUPPLY 800–168 10
INPUT/OUTPUT FILTER 800–193A 10
CONTROL BOARD 800–197 10
AUDIO BOARD 800–194 11
MODULATOR 800–195 11
MULTIPLIER BOARD 800–163 11
RF POWER AMPLIFIER 800–374B AND 800–373B 11
DUAL LINK STEREO STL 11
TEST EQUIPMENT 14
TOOLS FOR ALIGNMENT OF STL–10A SERIES TRANSMITTERS 14
Marti Electronics 2000
ALL RIGHTS RESERVED
Printed in the U.S.A.

ii
DESCRIPTION PAGE NO.
TUNE–UP PROCEDURE FOR STL–10A 14
MODULATOR CIRCUIT BOARD 800–195 ADJUSTMENTS 14
STL–10A TRANSMITTER TEST REPORT 15
AUDIO CIRCUIT BOARD 800–194 ADJUSTMENTS 16
MULTIPLIER CIRCUIT BOARD 800–163 ADJUSTMENTS 16
RF POWER AMPLIFIER BOARD 800–374B AND 800–373B 16
ADJUSTMENTS
POWER CONTROL POT CALIBRATION 16
B+ ADJUST 17
FORWARD POWER METER ADJUST 17
REVERSE POWER METER ADJUST 17
PA CURRENT ADJUST 18
FREQUENCY MEASUREMENT 18
STL-10A PARTS LIST 22
STL-10A SCHEMATICS 33
LIST OF ILLUSTRATIONS
FIGURE NO. TITLE PAGE NO.
1 STL–10A TRANSMITTER 1
2 STEREO STL SYSTEM BLOCK DIAGRAM – 702–058 2
3 FCC EMISSION PROFILE (500 KHZ CHANNEL) DRAWING 12
4 FCC EMISSION PROFILE (200 KHZ CHANNEL) DRAWING 13
5 STL–10A TRANSMITTER BLOCK DIAGRAM 19
6 STL–10A ADJUSTMENT LOCATIONS 20
7 STL–10A MAIN FRAME 21
LIST OF TABLES
TABLE NO. DESCRIPTION PAGE NO.
1 STL–10A ELECTRICAL AND PHYSICAL 4
SPECIFICATIONS
2 STL-10A PARTS LIST 19

WARNING
THIS EQUIPMENT MUST BE OPERATED WITH A 3–CONDUCTOR
GROUNDED AC POWER RECEPTACLE.FAILURE TO USE A
PROPERLY GROUNDED RECEPTACLE MAY RESULT IN IMPROPER
OPERATION OR A SAFETY HAZARD.
LIMITED WARRANTY
The Seller warrants that, at the time of shipment, the
products manufactured by the Seller are free from de-
fects in material and workmanship. The Seller’s obliga-
tion under this warranty is limited to replacement or re-
pair 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 with
in one (1) year [two (2) years for STL systems] from
date of original shipment and goods are returned in ac-
cordance with Marti instructions.
b. Equipment, accessories, tubes and batteries not
manufactured by Marti are subject to only such adjust-
ments 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 dam-
ages, installation cost or other costs of any nature as a
result of the use of the products manufactured or sup-
plied by the Seller, whether used in accordance with in-
structions 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:
M ARTI Electronics
4100 North 24th Street
Quincy, Illinois 62301
The United States of America
COPYRIGHT NOTICE
2000 All Rights Reserved
Marti Electronics
No part of this manual may be reproduced, transmitted,
transcribed, stored in a retrieval system , or translated
into any language, natural or computer, in any form or
by any means, without the prior written permission of
Marti Electronics.
Artwork depicting circuitry in this manual is protected
by copyright laws.
Information in this manual is subject to change without
notice and does not represent a commitment on the part
of Marti Electronics.
Marti Electronics may make improvements and/or
changes in this manual or in the product described here-
in at any time.
This product could include technical inaccuracies or
typographical errors.
PHONE NUMBERS:
Sales (817) 735–8134
Sales FAX [phone]
Service (217) 224–9600
Service Fax [phone]

1
INTRODUCTION – STL–10A.
The MARTI STL–10A Studio Transmitter Link/Inter–city Relay is a line–of–sight FM communications system pro-
viding a high quality broadcast audio channel with two optional sub–channels. A dual link for stereo provides two
identical broadcast quality channels with better than 70 dB stereo cross–talk and four optional sub–channels. These
systems offer greater rejection of interference, superior noise performance, much lower channel cross–talk, and
greater redundancy than currently available composite STL systems.
APPLICATIONS OF THE STL–10A SYSTEM (FCC Approved Parts 74, 101):
•STL for FM stereo broadcast (dual system)
•STL for AM stereo broadcast (dual system)
•STL for FM monaural or AM monaural broadcast
•Inter–city relay for linking two or more broadcast facilities
•Multi–relay system for radio network distribution
•Communications link between satellite earth station and broadcast
facilities
•Data and Background Music links
•Private microwave service
Complex systems can be built from basic STL–10A transmitters and R–10 receivers having multiple relay (repeat-
ers), bi–directional (full duplex), and automatic switching hot standby features (refer to Figure 2).
Features of the STL–10A Transmitter include:
FCC approved under Parts 74 and 101.
User selectable audio processing provides 0, 25, 50, or 75 microsecond pre–emphasis
options.
Low–pass filters designed to eliminate overshoot on complex audio waveforms.
Calibrated RF watt meter for forward and reflected power.
Test meter on front panel indicates Subcarrier Level, Supply Voltage, PA Current, For
ward and Reflected Power. Additional test points are located inside transmitter.

2
FIGURE 2. STEREO STL SYSTEM BLOCK DIAGRAM – 702–058
COPYRIGHT 2000 MARTI ELECTRONICS

3
Automatic output power control. The power control maintains the output power to a
specific level and is independent of temperature and voltage changes.
Twelve segment bar graph for display of peak transmitter modulation. The five highest
LED’s (100% to 250%) have a “peak–hold” feature which will display instantaneous
peak value for one second, a valuable feature when dealing with pre–emphasized
program audio.
Automatic switching capability by addition of Model ATS–15E Transmitter Switcher
Accessory plug for external DC power, remote control, remote metering, and other
functions
Low power consumption for operation on AC, solar cell, battery, or other
single–polarity DC source. (Marti Model UPS–12 Uninterruptible Power System).
Terminal strip for a balanced 600 ohm audio input, BNC jack for unbalanced audio,
Sub 1, and Sub 2 inputs.
The Marti STL–10A system derives its excellence from Marti’s experience in supplying thousands of such systems
world–wide over the past thirty years. This equipment incorporates state–of–the–art technology and is manufactured
in modern, efficient facilities under high quality–control standards.
STL–10A System Specifications
Freq
Range
MHz Transmitter Maximum
Power Maximum Deviation Receiver
Receiver
IF
Bandwidth System Specifications
Frequency Response Distortion Noise
850–960 STL––10/950 10 watts ±50 KHz R–10/950 200 KHz ±0.25 dB, 20–15000 Hz 0.25% or less –80 dB or better
System specifications shown are for 200 KHz receiver IF bandwidth. Narrow band channels requiring 85 KHz IF
bandwidth have ±0.25 dB response, 0.3% distortion.
System Applications
Freq
Range
MHz Application FCC
Part
B.W.
Each
Channel Frequency Response Distortion Noise Channel
Separation
850–960 FM Stereo STL 74 200 KHz ±0.25 dB, 20–15000 Hz 0.25% or less –80 dB or better 80 dB
850–960 FM Stereo STL 74 150 KHz ±0.3 dB, 20–15000 Hz 0.3% or less –72 dB or better 72 dB
850–960 AM Stereo STL 74 100 KHz ±0.3 dB, 20–15000 Hz 0.3% or less –72 dB or better 72 dB
928–960 Data or Background Music 94 100 KHz ±0.3 dB, 20–15000 Hz 0.3% or less –72 dB or better 72 dB
928–960 4–channel Sat. Pgm. Feed 94 100 KHz ±0.3 dB, 20–15000 Hz 0.3% or less –70 dB or better 70 dB
Stereo System Differential Phase 0.5 degrees or less SPECIFICATIONS SUBJECT TO CHANGE WITHOUT NOTICE

4
TABLE 1. STL–10A ELECTRICAL AND PHYSICAL SPECIFICATIONS
(Sheet 1 of 2)
PARAMETER SPECIFICATION
ELECTRICAL
FREQUENCY BAND 850 MHz to 960 MHz as specified.
MAXIMUM POWER OUTPUT 10 watts, ±0.5 watts,850 to 960 MHz.
OUTPUT CONNECTOR UG–58 (Type N Female)
OUTPUT IMPEDANCE 50 Ohms
MODULATION Direct FM
STABILITY ±0.00025%
SPURIOUS EMISSIONS More than 60 dB below carrier.
AUTOMATIC CHANGEOVER Provision for automatic changeover by addition of
ATS–15E Automatic Switcher
AUDIO INPUTS Balanced 600 Ohms, +8 dBm, barrier strip.
BNC connectors for unbalanced input.
SUBCARRIER INPUTS Two BNC connectors for remote control and/or
subcarrier inputs. 50–600 ohms unbalanced, 3 V. P–P for
10% injection.
METERING/INDICATORS Precision “Peak–hold” Bar Graph Modulation Meter.
Illuminated RF Wattmeter indicates Forward Power,
Reflected Power. Test Meter reads PA Current,
Subcarrier Level, 13.5 Volt Supply, and RF Drive 1, RF
Drive 2. LED indicates Transmit.
CONTROLS TRANSMIT switch, TEST METER switch, POWER
ADJUST Pot.
POWER REQUIREMENTS 120–220 volts ac * 50–60 Hz, 80 watts. 13.5 volt dc at
4 Amperes.
AC POWER SUPPLY Precision, electronically regulated with
current/temperature limiting.
ACCESSORY CONNECTOR 15–pin “D” connector for dc power, remote control,
automatic changeover and remote power metering.
FUSE 4 Amp Slo–Blo for 115 V operation. 1.25 Amp
Slo–Blo for 230V operation. Type 3AG.
PHYSICAL
DIMENSIONS 19 in.(48.26 cm.) wide x 3.5 in. (8.89 cm.) high x
14 in. (35.56 cm) deep.
WEIGHT Net 11 pounds. Domestic packed 18 pounds.
Net 4.9 kilograms. Export packed 8.2 kilograms.
TYPE ACCEPTANCE NUMBER FCC ID: DDESTL–10–950
(FCC PART 101 & PART 74)

5
TABLE 1. STL–10A ELECTRICAL AND PHYSICAL SPECIFICATIONS
(Sheet 2 of 2)
PARAMETER SPECIFICATION
ENVIRONMENTAL
OPERATING TEMPERATURE –20°C to +50°C (–4°F to +122°F).
RANGE
*Voltage must be specified with order.
** Requires APS–28/18 Power Supply
UNPACKING AND INSPECTING.
This equipment was factory tested, inspected, packed, and delivered to the carrier with utmost care. Do not accept
shipment from the carrier which shows damage or shortage until the carrier’s agent endorses a statement of the irreg-
ularity on the face of the carrier’s receipt. Without documentary evidence, a claim cannot be filed.
Unpack equipment immediately upon receipt and thoroughly inspect for concealed damage. If damage is discov-
ered, cease further unpacking and request immediate inspection by a local agent of the carrier. A written report of
the agent’s findings, with his signature is necessary to support the claim. Check your shipment against the shipping
papers for possible shortage. Do not discard any packing material until all items are located. Small items are often
thrown away with packing material.
The packing material should be retained until equipment testing is completed. Any equipment returned to the
factory should be packed in the original cartons, insured, and pre–paid.
INSTALLATION.
NOTE
NOTE
INSTALL RACK–MOUNTED EQUIPMENT IN A WELL VENTI-
LATED, GROUNDED, AND SHIELDED RACK CABINET.
Install rack–mounted equipment in a well ventilated, grounded, and shielded rack cabinet. Do not locate solid–state
equipment in a rack above tube–type equipment which produces high temperatures. 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 equip-
ment 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 are at the same RF ground potential.
STL–10A TRANSMITTER INSTALLATION.
1. Program audio output is connected to balanced audio input screw terminals. Use shielded wire. Program audio
level required is +8 dBm, 600 ohms balanced and isolated from ground. For dual channel stereo repeat
instructions at second transmitter. Audio processing requirements will be discussed in OPERATION.
2. Connect a Remote Control or Subcarrier Generator (modulator) to the jack marked “J1 SUB IN”. The subcarrier
source may be 50 to 600 ohms impedance, and the input level required is approximately one (1) volt RMS.
Subcarrier frequencies may be between 39 KHz and 67 KHz. Systems factory supplied with 200 KHz IF
bandwidths will carry subcarriers up to 92 KHz. For other subcarrier frequencies or narrow IF bandwidth
systems contact the factory. A second subcarrier generator can be connected to J3. If a dual channel stereo STL
is used connect one subcarrier generator to J1 on each channel’s transmitter.

6
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 transmitting antenna coax to “J6 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.
WARNING
WARNING
THIS EQUIPMENT MUST BE OPERATED WITH A 3–PRONG,
GROUNDED, 115 VOLT, AC OUTLET RECEPTACLE. FAILURE
TO USE A PROPERLY GROUNDED OUTLET COULD RESULT
IN A SAFETY HAZARD OR FAULTY EQUIPMENT
PERFORMANCE.
5. For dual channel stereo, use only Marti Part No. 585–017, 20.5 inch double shielded jumper between J6 of each
transmitter and the indicated connectors of the HRC–10B Series Combiners. Use a third Part No. 585–017
jumper between the “ANTENNA” connector of the HRC–10B and the semi–rigid coax. Refer to Drawing
702–058.
6. Turn transmitter off. Connect the ac line receptacle on back of the transmitter to a 115 volt AC power source
with special cord set supplied. Use only 3–prong grounded outlet receptacles.
ANTENNA INSTALLATION.
STL Antenna Installation Checklist.
The following suggestions are offered to help those responsible for antenna installations avoid costly errors in as-
sembly and adjustment. Marti Electronics Inc. assumes no responsibility for the installation and performance of
antenna systems associated with the equipment. The following text presents a listing of some of the most frequently
asked questions associated with the equipment. The text is not intended to be a complete step–by–step procedure.
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 elements which
must be installed in the same plan as the reflector grids. In other words, if the reflector grid elements are horizontal,
then the feed dipole elements must also be horizontal. Cross polarization of grid and feed dipole will result in total
loss of antenna gain.
Transmission Line Connector Assembly.
Do not use RG–58 U or RG–8 U cable for STL station antennas. They have too much loss at VHF and UHF fre-
quencies. Follow the instructions furnished by the manufacturer when cutting the coaxial cable. Inspect the cable
ends for small metal fragments which can short–circuit the line inside the connector assembly. Check the line for a
short–circuit condition after each connector is installed using an Ohmmeter. Pressurized line should be checked for
several days under pressure before installation on a tower to ensure that there are no leaks in the line or fittings.
Moisture Proofing Coax Connectors and Fittings.
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 absorb moisture absorption which is difficult to detect and
remedy. Therefore, keep the line dry while in storage with the ends tightly capped. Coaxial splices, connectors, and
fittings, to be located outside should be made mechanically tight, then coated with a weather–proofing material such
as SCOTCHKOTE over at least two layers of SCOTCH 88 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.

7
Location and Grounding of Coaxial Cable.
Keep the STL receiver coaxial cable as far from the broadcast transmitter and coaxial cable as possible. 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 is essential that the STL antenna system be properly grounded for safety and proper operation. Ensure the antenna
system is properly grounded.
Antenna Installation and Adjustment.
The polarization of the transmit and receive antennas of the STL system must be the same. This means that if the
transmitting antenna is horizontal, the receiving antenna must also be horizontal. 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 ad-
justed, 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).
If the antenna system fails to give the predicted signal strength level, check the following items:
1. Check for correct assembly of antenna.
2. Ensure the antennas have same polarity.
3. Check orientation of antennas in both horizontal and vertical directions.
4. Check VSWR of both the transmit and receive antennas. VSWR should be less than 1.5:1.
5. Check for required Fresnel zone path clearance at all points along radio path.
6. Check for obstructions in the path such as trees and man–made structures. Do not depend on maps or aerial
photographs.
WARNING
WARNING
YOU CAN BE KILLED IF AN ANTENNA COMES IN CONTACT
WITH ELECTRIC POWER LINES OR EXPOSED ELECTRICAL
WIRING. FOR YOUR SAFETY USE EXTREME CAUTION WHEN
INSTALLING ANTENNAS. KEEP AWAY FROM POWER LINES.
OPERATION.
SWITCH AND METER FUNCTIONS.
TRANSMIT–OFF Switch & LED.
This toggle switch controls the RF output of the transmitter. The red LED above this switch is a visual indication
that the switch is in “TRANSMIT” position. The audio circuits, the 13.5 volt regulated power supply and the meter
illumination lamps remain on when the TRANSMIT switch is “OFF”.

8
FORWARD–REFLECTED Switch & RF Power Meter.
The RF POWER METER, with its selector switch, allows monitoring parameters within the transmitter as
follows:
1. When switched to “FORWARD POWER”, the meter indicates the RF power output of the STL–10A
transmitter. The maximum power is 10 Watts for the 850–960 MHz band (United States).
2. When switched to “REFLECTED POWER”, the TEST METER indicates the amount of power returning on
the coaxial line from the antenna. This is useful in determining the VSWR (Voltage Standing Wave Ratio) for the
antenna system. The lower the VSWR for a given forward power, the better. Most antennas guarantee a VSWR
of less than 1.5 to 1.
The table below gives VSWR for various reflected powers:
Forward
Power Reflected
Power
VSWR
10 Watts (890–960 MHz) 0.3 watts 1.40
10 Watts (890–960 MHz) 0.4 watts 1.50
10 Watts (890–960 MHz) 0.5 watts 1.57
10 Watts (890–960 MHz) 0.7 watts 1.70
10 Watts (890–960 MHz) 1.0 watts 1.90
PEAK MODULATION Meter.
A “peak–hold” twelve segment bar graph display is included on the STL–10A transmitter for setting and monitor-
ing peak STL modulation (composite or mono mode). The five highest LED’s (100% to 250%) have a “peak–hold”
feature which will display an instantaneous peak value for one second. This is a valuable feature when dealing with
pre–emphasized program audio. The procedure for setting peak modulation is to adjust audio input level into the
STL–10A until the 100% bar is flashing on audio peaks. The 110% through 250% bars indicate over–modulation
and require a reduction in input level to obtain a 100% peak indication.
TEST Meter.
The TEST METER with its selector switch, allows monitoring of five important parameters within the transmitter
as follows:
1. “SUB LEVEL” – Indicates subcarrier injection. 0 VU is approximately 20% injection. For 10% injection use
–6 VU. Subcarrier voltage at J1 or J3 is approximately 1 volt for 20% injection, 0.5 volts for 10%.
2. “+13 VOLT SUPPLY” – Indicates regulated voltage supply operation. +1.5 VU is approximately 13.5 VDC.
3. “P.A. CURRENT” – The collector current of the final amplifier and its driver is calibrated to read “0 VU” on
the meter at rated power output and efficiency. The POWER ADJUST potentiometer should never be set to
produce a P.A. current greater than 0 VU.
4. “FORWARD POWER”. The transmitter forward power level.
5. “REFLECTED POWER”. The transmitter reflected power level.

9
PRE–EMPHASIS SWITCHES.
Two programmable switches S1 and S2 on audio board 800–194 enable the user to select flat, 25, 50, or 75
micro–second pre–emphasis characteristics. The selection of one of these options in the transmitter requires a
corresponding selection of S1 and S2 on receiver audio board 800–205. Refer to STL–10A adjustment location dia-
gram at the end of this manual for the location of these switches. The switches, as shown in the diagrams, are
positioned for 75 micro–seconds at the factory. 75 micro–second pre–emphasis and de–emphasis produces the best
threshold noise performance in an FM system. It does however present problems in modulation control. Some
users therefore may wish to use 50 micro–second, 25 micro–second, or flat processing. AM stations will find flat
processing desirable since the STL can be treated as a pair of wires in proof of performance tests without possible
overmodulation of the link at high audio frequencies. With 75 micro–second pre–emphasis, audio input levels to the
transmitter should be reduced 20 dB below 100% modulation when running frequency response tests to prevent
overmodulation at the higher audio frequencies. With a full quieting RF signal into the receiver, flat pre–emphasis
will produce a system signal–to–noise ratio approximately 6 dB less than 75 micro–second pre–emphasis. Received
signal levels less than full quieting may produce a difference of as much as 13 dB between flat and 75 micro–second
pre–emphasis.
FREQUENCY MEASUREMENT.
The RF output frequency of this transmitter should be measured and adjusted as often as necessary to insure
on–frequency operation and to comply with regulations (refer to TUNE–UP PROCEDURE in the following text).
STL–10A SYSTEM PERFORMANCE TESTS.
The STL–10A transmitter, R–10 receiver with the associated antenna system can be tested and compared with facto-
ry test data included in this manual. The following procedures 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 microvolts is given under OPERATION in the R–10 receiver manual. For a 950
MHz system using 50 KHz FM deviation, typical noise levels are:
1 uV for 20dB S/N ratio
3 uV or 50 dB S/N ratio
10 uV for 60 dB S/N ratio
20 uV for 70 dB S/N ratio
50+ uV for ultimate S/N ratio
For the above system with 20% subcarrier injection, the following noise level on the subcarrier
(Marti SCG–10 – SCD–10 System) was measured: (no modulation main or sub).
10 uV for 40 dB Subcarrier S/N ratio
20 uV for 47 dB Subcarrier S/N ratio
30 uV for 50 dB Subcarrier S/N ratio
150 uV for ultimate Subcarrier S/N ratio
With ultimate S/N ratio, main to sub crosstalk should be –40 to –45 dB (using Marti SCG–10 – SCD–10 Subcarrier
System).

10
NOISE.
Noise measurements should be made first, since high noise levels will influence distortion readings. Also ground
loops in the audio oscillator to transmitter connections and distortion analyzer to receiver connections 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 “PGM LEVEL ADJ” pot for +10 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.
DISTORTION.
Harmonic distortion is usually measured at 100% modulation and at several frequencies. If pre–emphasis processing
is used in the transmitter with corresponding 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 transmitter/receiver
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.
If the STL–10A System is switched to flat processing, frequency response can be measured as if the signal were be-
ing sent over straight wires. If pre–emphasis processing is used (especially 75 micro–seconds) allowance must be
made in the transmitter audio input level to prevent 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 limits published in the SYSTEM SPECIFICATIONS.
STL–10A THEORY OF OPERATION.
Refer to the STL–10A block diagram in the DRAWINGS AND PARTS LIST section for the following discussion.
POWER SUPPLY 800–168.
Power supply circuit board 800–168 contains filter capacitor C5, and reverse polarity protection diodes D5, D6 and
D7. The unregulated output voltage of this supply is 17–20 volts. The voltage is supplied from bridge rectifier
D1–4 on circuit board 800–168.
INPUT/OUTPUT FILTER 800–193A.
Radio–frequency filters are installed on all input/output circuits connected to ACCESSORY connector J4, as well as
the AC line input.
CONTROL BOARD 800–197.
Applies an operating voltage to the unit.

11
AUDIO BOARD 800–194.
The 600 ohm balanced audio input to the transmitter is connected to the inputs of unity gain differential amplifier
IC–1A. Potentiometer R9 is provided for adjusting the amplifier to produce the maximum common mode rejection
(CMR). The output of the differential amplifier is directly coupled to the pre–emphasis amplifier. The negative
feedback circuit of this amplifier has two capacitors selected by switches S1 and S2 which provides options of 0, 25,
50, or 75 microsecond pre–emphasis. Following the pre–emphasis circuit are two stages of active Butterworth low–
pass filtering. The signal is then routed to the MODULATOR audio input and to metering amplifiers IC–3A and
IC–3B. The subcarrier input is routed to the MODULATOR subcarrier input.
MODULATOR 800–195.
The MODULATOR consists of voltage controlled crystal oscillator Q2, buffer amplifier Q3, subcarrier modulator
D2, precision voltage regulator IC–1 and oven heater control Q1. Precise frequency control is obtained by thermally
coupling components Y–1, Q1, Q2, and IC–1 to temperature regulated frequency control module 800–160–1.
Coarse and fine frequency adjustment is provided by L1 and L2 while the main channel modulation is provided by a
voltage variable capacitance diode in the frequency control module. Bias for this diode is obtained through voltage
divider resistors R4, R5, and R7. Diode D1 temperature compensates the bias supply. Components L3, C13 and D2
permit phase modulation of the subcarrier information upon the RF output of transistor Q3.
MULTIPLIER BOARD 800–163.
The modulator RF output is frequency–multiplied in the multiplier board to obtain the various operating frequencies
listed on the STL–10A specification sheet. The power level at the input to the multiplier is approximately 5 mw.
The output level is 0.7 to 1.2 watts.
RF POWER AMPLIFIER 800–374B AND 800–373B.
The RF power amplifier consists of two boards; the PA Interface board (800–374B) and the Two–Stage RF Power
Amplifier board (800–373B). Up to 1 watt RF power from the Multiplier board (800–163) at a frequency ranging
from 445 to 480 MHz is fed into the 10/15C PA Interface board (800–374B). The purpose of this board is to double
the incoming frequency, amplify the doubled frequency and filter out all other frequencies. This board also provides
a means for controlling the RF power level via the front panel POWER ADJUST POT. An automatic level control
(ALC) circuit stabilizes and maintains an accurate output power level. A 50 mW (max), 890–960 MHz signal from
this board is fed into the two stage RF Power Amplifier board. The RF goes through two stages of RF amplification.
The first stage (U2) is a 1 watt (max) pre–driver. It has an input and output transformer (T1 and T2) for achieving
optimum 50 ohm matching between the stages. The output of T2 is fed into the final PA module (U3) for an output
of 15 watts max. The signal is then low–passed filtered through FL1 and then fed through a directional coupler for
monitoring forward and reflected power. This board also provides regulated B+ for powering the PA and the rest of
the chassis. Finally, there also exist circuitry for regulating the fan and monitoring PA current.
DUAL LINK STEREO STL.
Two STL–10A Links can share the same 500 KHz, 300 KHz, or 200 KHz channel for transmission of left and right
stereo components, as shown in the STEREO STL SYSTEM BLOCK DIAGRAM, Drawing No. 702–058. A system
operating in this manner uses no more spectrum (and possibly less) than “COMPOSITE” systems, while providing
much lower channel cross–talk (72 dB). Since the two links are independent, if one link fails, continued operation in
mono service is assured. Phase shift between channels can be less than 1 degree. The two carriers are offset above
and below the channel center frequency as shown in the following FCC EMISSION PROFILE Drawings. Offsets are
125 KHz for 500 KHz channels, 75 KHz for 300 KHz channels, and 50 KHz for 200 KHz channels. Using a Marti
HRC–10 Transmitter Combiner having 40 dB isolation, all sidebands and IM products are well within the limits of
Subpart E of FCC Rules Part 74.535. Optional transmitter combiners are available which provide 70 dB or 100 dB
of isolation. Receiver IF selectivity required in this system is 200 KHz for 500 KHz channels, 85 KHz for 300 KHz
channels and 75 KHz for 200 KHz channels.

12
COPYRIGHT 2000 MARTI ELECTRONICS
FIGURE 3. FCC EMISSION PROFILE (500 KHZ CHANNEL) DRAWING

13
FIGURE 4. FCC EMISSION PROFILE (200 KHZ CHANNEL) DRAWING
COPYRIGHT 2000 MARTI ELECTRONICS

14
TEST EQUIPMENT.
The following text presents the test equipment required for alignment of STL–10A Transmitters. A sample test re-
port is also provided in the following text.
1. Bird, Model #43, Wattmeter, 50 ohm impedance.
2. Bird, 25–Watt Element, 400–1000 MHz.
3. Microwave Associates, 50–Watt RF Load, Model 44003.
4. Kron–Hite, Distortion Analyzer, Model 6900B.
5. Kron–Hite, Oscillator, Model 4500.
6. Hewlett Packard, Attenuator Set, Model 350D.
7. Signoteck Frequency Counter.
8. Hewlett Packard, Spectrum Analyzer, Model 8558B.
9. Wavetek, Automatic Modulation Meter, Model 4101.
10. Wavetek, Digital Multimeter, Model 27XT.
12. Kay, RF Attenuator, Adjustable 0–110 dB, Model 437A.
13. Marconi, RF Signal Generator, Model 2022C.
TOOLS FOR ALIGNMENT OF STL–10A SERIES TRANSMITTERS.
1. GC, 9300, Tuning Tool.
2. GC, 9440, Tuning Tool.
3. Spectrol, 8T000, Tuning Tool.
4. Sprague–Goodman, Tuning Tool.
TUNE–UP PROCEDURE FOR STL–10A.
MODULATOR CIRCUIT BOARD 800–195 ADJUSTMENTS.
Connect a dummy load with a sampling attenuator to the ANTENNA connector J6 of the transmitter. Connect an
accurate standard FM deviation meter and frequency counter to the sampling attenuator or J5 the FREQUENCY
TEST JACK. Operate the CONTROL switch to TRANSMIT.
1. Measure the bias voltage at TP (test point) of modulator circuit board 800–195 using digital dc voltmeter.
This voltage should be recorded on STL–10A TRANSMITTER TEST REPORT. To ensure low distortion
modulation, do not change this voltage setting.
2. Operate the transmitter on frequency by adjusting L2 (fine) coil slug using correct insulated tool. If
necessary, L1 (coarse adjustment) can be made using the insulated tool specified.
3. Monitor the PEAK MODULATION LED bar and feed a 400 Hz, +8 dBm signal from an audio signal
generator into TB–1. The PEAK MODULATION meter should read 100%. If not, adjust R24 (modulation
meter calibrate) on audio circuit board 800–194 for 100% on PEAK MODULATION meter. The FM
deviation meter should read the deviation specified under 100% modulation on STL–10A TRANSMITTER
TEST REPORT. If not, adjust R6 on modulator circuit board 800–195.
4. Remove the 400 Hz tone. Feed the audio signal generator set for 67 KHz at one (1) volt into J1 Sub In.
Operate the TEST METER switch to SUB LEVEL and adjust audio signal generator level for a meter reading
of 0 VU. Adjust R11 for a 20% sub–carrier injection as indicated on the linear vertical display on a spectrum
analyzer.

15
STL–10A TRANSMITTER TEST REPORT
CUSTOMER: _________________________________________________________________________
ADDRESS: ___________________________________________________________________________
FREQUENCY: ______________________________
Serial #: ______________________________
Modulator Bias: __________________
100% Modulation __________________________ +kHz.
Total DC Current __________________________ amperes
TEST POINT READINGS
TP 1 __________ 0.15 V dc – 0.60 V dc
TP 2 __________ 0.70 V dc – 1.90 V dc
TP 3 __________ 0.50 V dc – 1.00 V dc
TP 4 __________ 0.50 V dc – 1.90 V dc
TEST METER READINGS
Subcarrier Level: 0 VU = 20%
+13 Volt Supply: +1 VU = 13.5 Volts DC
P.A. Current: 0 VU = Normal
TEST EQUIPMENT
Frequency Counter, HP Model 5383A
Deviation Monitor, Wavetek Model 4101
SIGNATURE: ______________________________________
DATE: ____________________________________________

16
AUDIO CIRCUIT BOARD 800–194 ADJUSTMENTS.
1. Connect an audio voltmeter to Pin 1 (modulator audio) of audio circuit board 800–194. Connect a jumper
between terminal 1 and 2 (the outer terminals) of TB–1 (the 600 ohm balanced input). Connect an audio
signal generator between chassis and either Terminal 1 or 2. Operate the generator for a 100 Hz output at
1 volt. Increase sensitivity of the audio voltmeter until the 100 Hz output component is indicated. Adjust R9
(CMR, Common Mode Rejection) for a minimum common mode output.
2. Set S1 and S2 on audio circuit board 800–194 for 75 micro–second pre–emphasis with S1 and S2 positioned
toward R15. Remove the jumper and feed the audio signal generator into terminals 1 and 2 of TB–1.
Operate the generator to 15 KHz and adjust the level for 0.78 volts (0 dBm) output on the audio voltmeter.
Operate the generator to 400 Hz and observe audio voltmeter. The level at 400 Hz should be exactly 17 dB
below the level at 15 KHz. If not, return to 15 KHz and adjust R15 by the amount in error at 400 Hz. Repeat
process until the exact pre–emphasis is obtained.
3. Modulation meter calibration is covered in the modulator circuit board 800–195 adjustments.
MULTIPLIER CIRCUIT BOARD 800–163 ADJUSTMENTS.
Remove the top cover of the unit. Remove the coaxial cable plug at RF Output jack J2 of on multiplier circuit board
800–163. Refer to the STL–10A ADJUSTMENT LOCATIONS diagram for the location of connectors, test points
and adjustments.
1. Connect a Bird Model #43 Wattmeter with a 5–watt element and a 50 ohm load to J2 of multiplier circuit
board 800–163. Connect sensitive multimeter (0–3 volt DC range) negative probe to TP–1 of multiplier
board and the positive probe to chassis ground. Operate the CONTROL switch to TRANSMIT. A minimum
of 0.25 volts should be indicated. If not, refer to MODULATOR CIRCUIT BOARD ADJUSTMENTS in
the preceding text.
2. Move the meter negative probe to TP–2. Adjust L1 and L2 for a maximum indication.
3. Move the meter negative probe to TP–3. Adjust L3 and L4 for a maximum indication.
4. Move the meter negative probe to TP–4. Adjust L5 and L6 for a maximum indication.
NOTE: Omit this step on the 140–180 MHz units.
5. Move the meter negative probe to TP–5. Adjust C27 and C28 for a maximum indication. Turn “POWER
ADJUST” pot, R14 for maximum power.
6. Adjust C36 and C37 for a maximum indication on the wattmeter connected to J2 with the R14 power pot
operated to maximum. Adjust power level to .75 to 2 watts output.
7. Operate the CONTROL switch to OFF. Remove the wattmeter from J2 and re–install coaxial cable plug at
J2. Adjust R14, “POWER ADJUST”, for correct transmitter output power.
RF POWER AMPLIFIER BOARD 800–374B AND 800–373B ADJUSTMENTS.
The RF Power Amplifier is very broad–band and has been fully calibrated and adjusted at the factory. The only
adjustments available are POWER CONTROL POT calibration, B+ adjust, FORWARD POWER METER adjust,
REFLECTED POWER METER adjust, and PA CURRENT adjust. These adjustments should only be made as
necessary and with extreme care by following the procedures below:
For the following adjustments, switch “TRANSMIT” off and connect an accurate RF wattmeter and dummy load
rated for at least 25 watts at 800 to 1000 MHz to the RF output “N” connector. Remove top cover of unit. Please
carefully read procedures before doing them.
POWER CONTROL POT CALIBRATION.
1. On the Interface board, rotate the POWER CALIBRATION POT (R4) fully counter–clockwise.
2. On the front panel of unit, rotate the POWER CONTROL POT fully counter–clockwise.
3. Rotate R20 on the two–stage RF power amplifier board fully counter–clockwise.