Marti Electronics SR-20M User manual

MARTI
ELECTRONICS
STL RECEIVER
MODELS: SR–20M
SR–20C
October, 2003 IM No. 597–8105

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WARNING
THIS EQUIPMENT MUST BE OPERATED WITH A 3–PRONG
GROUNDED OUTLET RECEPTACLE. FAILURE TO USE A
PROPERLY GROUNDED OUTLET MAY RESULT IN
IMPROPER OPERATION OR SAFETY HAZARD!
LIMITED WARRANTY
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 replacement 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 adjustments as
Marti may obtain from the supplier thereof.
c. This warranty does not apply to equipment that has been altered, improperly handled, or damaged in any way.
The Seller is in no event liable for consequential damages, installation cost or other 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:
Broadcast Electronics
MARTI Electronics Division
4100 North 24th Street
Quincy, IL 62301
The United States of America
COPYRIGHT NOTICE
2003 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.

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Copyright laws protect artwork depicting circuitry in this manual.
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 herein at any
time.
This product could include technical inaccuracies or typographical errors.
PHONE NUMBERS:
Sales (817) 735–8134
Service (217) 224–9600
FAX [phone]

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ABOUT THIS MANUAL
This manual supports both the SR–20M and SR–20C STL receivers for all standard frequency bands. The manual
will be revised as new frequency bands become available.
Manual Part Numbers:
Kit, Binder And Manual: 979–9998
Manual Only 597–8105

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TABLE OF CONTENTS
Introduction 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Specifications & Ordering 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Unpacking & Inspecting 8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Installation 9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Antennas 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Operation 17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
System Performance Tests 21. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Theory of Operation 23. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Test Equipment 25. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Tools For Alignment 25. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Tune–up and Adjustments 26. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Schematic and Assembly Drawings 30. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

INTRODUCTION
See the SPECIFICATIONS & ORDERING section for a listing of available frequency
ranges.
SR–20M MONO STL RECEIVER
SR–20C COMPOSITE STL RECEIVER

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The Marti STL Transmitters with companion SR–20C and SR–20M Receivers form a high quality FM, syn-
thesized, point–to–point, line of sight, studio–to–transmitter link with two optional sub–channels. A dual link con-
sisting of two SR–20M systems for stereo provides two identical broadcast quality channels with better than 70 dB
stereo cross–talk and four optional sub–channels. Complex systems can be built from basic STL transmitters and
SR–20M/SR–20C receivers having multiple relay (repeaters), bi–directional (full duplex), and automatic switching
hot standby features.
The SR–20M receiver is a monophonic single channel unit that can be programmed on any frequency within a
50 MHz band. The SR–20C is a composite frequency agile receiver. The SR–20C can be programmed for any
frequency within a 50 MHz band. Each SR–20M and SR–20C STL receiver is offered in a wide range of band
models. Refer to the SPECIFICATIONS & ORDERING section for a listing of available frequency ranges.
The SR–20M/SR–20C receivers operate from: 1) an 85 to 264 volt, 47 to 63 Hz AC source or 2) a +10 to +14
volt DC source. SR–20M units are equipped with a multimeter and meter select switch for the monitoring of signal
level, subcarrier level, power supply voltage, and program output level parameters. SR–20C units are also equipped
with a multimeter and meter select switch for the monitoring of signal level, subcarrier level, power supply voltage,
monophonic program output level, and composite output level parameters. A front panel attenuation switch allows
the input level to be adjusted to minimize any IMD products. Additional front panel controls include: 1) a mono-
phonic program output level control, 2) a squelch control, and 3) a composite level control for SR–20C units. The
SR–20M/SR–20C front panel indicators include: 1) MAX signal, 2) ATT signal, 3) UNSQUELCHED, 4) POWER,
and 5) AFC LOCK.
STL Transmitter/SR–20M Applications:
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
STL Transmitter/SR–20C Applications:
•Composite FM Stereo audio with subcarrier
•Monophonic audio with two subcarriers
•Digital stereo audio (requires external modems)
•Multi–channel audio or data (requires external MUX)
•Digital data (requires external modems)

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SR–20M/SR–20C Features:
•Mechanical – 19 inch rack mount design
•Wideband operation – 50 MHz
•SR–20M Models – Monophonic single channel operation within a 50 MHz band
•SR–40C Models – Composite frequency agile operation within a 50 MHz band
•Operation from: 1) 85V to 264V, 47 to 63 Hz AC source or 2) an external +10 to +14
VDC source
•Frequency synthesized dual stage RF converter module with Automatic Frequency
Control (AFC)
•Front panel signal attenuation control – used to minimize IMD products
•Front panel squelch control
•Front panel headphone control and receptacle
•A microcontroller programmed to perform the following functions:
•Front–panel switch and indicator control
•AFC lock control
•Metering control
•Auto recovery from loss of ac/dc power
•Squelch relay with contacts available for external switching

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SPECIFICATIONS & ORDERING
SR–20M STL Receiver
Frequency Bands: See ORDERING INFORMATION below.
Type of technology to produce op-
erating frequency: Phase–locked loop; synthesized.
Operating Temp. Range: –10ºC to +50ºC.
Frequency Stability (over operat-
ing temperature range): 0.0001 %.
SR–20M Signal–to–Noise
@ 100 uV:
200 kHz BW @ 50 kHz Dev
125 kHz BW @ 15 kHz Dev
125 kHz BW @ 9 kHz Dev
Greater than 77 dB.
Greater than 66 dB.
Greater than 62 dB.
Frequency Response: ±0.25 dB, 20 Hz to 15 kHz.
Distortion @ 100 uV:
200 kHz BW @ 50 kHz Dev
125 kHz BW @ 15 kHz Dev
125 kHz BW @ 9 kHz Dev
0.25% or less, 20 Hz to 15 kHz.
0.3% or less, 20 Hz to 15 kHz.
0.3% or less, 20 Hz to 15 kHz.
Spurious Response: –90 dB.
RF Input Impedance: 50 ohms.
RF Connector: Type N–Female.
Output Level: –10 to +11 dBm .
Output Impedance: Balanced, 600 Ohms – terminal strip/15 pin D–Type. Unbalanced 600
Ohms – BNC.
Sensitivity: 3 microvolts for 50 dB signal–to–noise.
10 microvolts for 60 dB signal–to–noise.
100 microvolts for maximum signal–to–noise, typically 75 dB or greater.
Metering/Indicators: Illuminated meter indicates: 1) signal level, 2) subcarrier level, 3) power
supply level, and 4) mono program output level. LEDs – MAX Signal,
ATT Signal, UNSQUELCHED, POWER supply, and AFC LOCK.
Front Panel Controls: SIGNAL ATTENUATION, MONO PROGRAM OUTPUT LEVEL,
SQUELCH LEVEL, meter selection control, HEADPHONE level control.
Power Requirements: 85 to 264 VAC, 47 to 63 Hz.
External DC operation – +10 to +14 VDC.
Approximate AC Current Re-
quirements: 1.5 Amps.
Accessory Connector: Terminal strip or 15 pin D–Type.
Weight: Net 7.6 pounds.(3.5 kilograms).
Dimensions: 3.5 in. high x 19 in. wide x 15 in. deep.
(8.9 cm. high x 48.3 cm. wide x 38.1 cm. deep.)
Regulatory: FCC, DOC.

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SR–20C STL Receiver
Frequency Bands: See ORDERING INFORMATION below.
Type of technology to produce op-
erating frequency: Phase–locked loop; synthesized.
Operating Temp. Range: –10ºC to +50ºC.
Frequency Stability (over operat-
ing temperature range): 0.0001%.
Monophonic Signal–to–Noise
@ 100 uV:
200 kHz BW @ 50 kHz Dev
125 kHz BW @ 15 kHz Dev
125 kHz BW @ 9 kHz Dev
Greater than 75 dB.
Greater than 64 dB.
Greater than 60 dB.
Monophonic Frequency
Response: ±0.2 dB, 20 Hz to 15 kHz.
Monophonic Distortion
@ 100 uV:
200 kHz BW @ 50 kHz Dev
125 kHz BW @ 15 kHz Dev
125 kHz BW @ 9 kHz Dev
0.25% or less, 20 Hz to 15 kHz.
0.3% or less, 20 Hz to 15 kHz.
0.3% or less, 20 Hz to 15 kHz.
Composite Signal–to–Noise: Greater than 75 dB, dependent upon the operating frequency, demodu-
lated, deemphasized.
Composite Frequency Response:
Composite
Wideband ±0.2 dB, 30 Hz to 53 kHz.
±0.3 dB, 30 Hz to 100 kHz.
Composite Distortion: 0.2% or less, 20 Hz to 15 kHz, demodulated, deemphasized, low–pass
filtered, left or right channel.
Spurious Response: –90 dB.
RF Input Impedance: 50 ohms.
RF Connector: Type N–Female.
Monophonic Output Level: –10 to +11 dBm.
Monophonic Output Impedance: Balanced, 600 Ohms – terminal strip/15–pin D–Type.
Composite Output Level: 0.25V to 8V p–p.
Sensitivity: 4 microvolts for 50 dB signal–to–noise.
14 microvolts for 60 dB signal–to–noise.
100 microvolts for maximum signal–to–noise, typically 75 dB or greater.
Metering/Indicators: Illuminated meter indicates: 1) signal level, 2) subcarrier level, 3) power
supply level, 4) mono program output level, and composite program out-
put level. LEDs – MAX Signal, ATT Signal, UNSQUELCHED, POWER
supply, and AFC LOCK.
Front Panel Controls: SIGNAL ATTENUATION, MONO PROGRAM OUTPUT LEVEL,
COMPOSITE OUTPUT LEVEL, SQUELCH LEVEL, meter selection
control, HEADPHONE level control.
Power Requirements: 85 to 264 VAC, 47 to 63 Hz.
External DC operation – +10 to +14 VDC.
Approximate AC Current Re-
quirements: 1.5 Amps.
Accessory Connector: 15–pin D connector or terminal strip.