---
title: "T011: Description Of The"
description: "Official Cospas-Sarsat T-series document T011"
sidebar:
  badge:
    text: "T"
    variant: "note"
# Extended Cospas-Sarsat metadata
documentId: "T011"
series: "T"
seriesName: "Technical"
documentType: "specification"
isLatest: true
issue: 2
revision: 6
documentDate: "October 2025"
originalTitle: "Description Of The"
---

> **📋 Document Information**
>
> **Series:** T-Series (Technical)
> **Version:** Issue 2 - Revision 6
> **Date:** October 2025
> **Source:** [Cospas-Sarsat Official Documents](https://www.cospas-sarsat.int/en/documents-pro/system-documents)

---

# T011 - T011-OCT-23-2025.pdf

**Pages:** 62

---


DESCRIPTION OF THE 
406-MHz PAYLOADS USED IN THE 
 COSPAS-SARSAT GEOSAR SYSTEM 
C/S T.011 
Issue 2 – Revision 6 


DESCRIPTION OF THE 406-MHz PAYLOADS USED  
IN THE COSPAS-SARSAT LEOSAR SYSTEM 
 
 
 
History 
 
Issue 
Revision 
Date 
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Approved (CSC-73) 


TABLE OF CONTENTS 
 
Page 
 
History  ................................................................................................................................................. i 
Table of Contents  ................................................................................................................................. ii 
List of Figures 
 ................................................................................................................................ iv 
List of Tables 
 ................................................................................................................................. v 
1. 
INTRODUCTION .............................................................................................. 1-1 
1.1 
Overview .............................................................................................................. 1-1 
1.2 
Purpose ................................................................................................................. 1-1 
1.3 
Scope .................................................................................................................... 1-1 
1.4 
Reference Documents .......................................................................................... 1-1 
2. 
COSPAS-SARSAT PARAMETERS ................................................................ 2-1 
2.1 
406 MHz GEOSAR Payload Functional Description .......................................... 2-1 
2.2 
GEOSAR Orbit Summary .................................................................................... 2-2 
2.3 
GEOSAR System Coverage ................................................................................. 2-2 
3. 
COSPAS-SARSAT REPEATERS .................................................................... 3-1 
3.1 
GOES Repeater Functional Description .............................................................. 3-1 
3.1.1 GOES 15 and Before ................................................................................ 3-1 
3.1.2 GOES 16 and Later .................................................................................. 3-2 
3.2 
GOES Repeater Operating Modes ....................................................................... 3-3 
3.3 
GOES Repeater Spectrum Characteristics ........................................................... 3-4 
3.3.1 All GOES up to GOES-15 ....................................................................... 3-4 
3.3.2 GOES 16 and Later .................................................................................. 3-7 
3.4 
GOES Repeater Coverage Area ........................................................................... 3-7 
3.5 
GOES Repeater Performance Parameters ............................................................ 3-8 
3.5.1 GOES SAR Receiver Parameters ............................................................. 3-8 
3.5.2 GOES SAR Transmitter Parameters ...................................................... 3-10 
3.5.3 GOES SAR Antennas ............................................................................. 3-10 
4. 
INSAT/GSAT 406 MHz GEOSAR REPEATER ............................................ 4-1 
4.1 
INSAT/GSAT Repeater Functional Description .................................................. 4-1 
4.2 
INSAT/GSAT Repeater Operating Modes .......................................................... 4-2 
4.3 
INSAT/GSAT Repeater Spectrum Characteristics .............................................. 4-2 
4.4 
INSAT/GSAT Repeater Coverage Area .............................................................. 4-4 


4.5 
INSAT/GSAT Repeater Performance Parameters ............................................... 4-6 
4.6 
INSAT/GSAT SAR Antennas .............................................................................. 4-6 
5.
ELECTRO-L GEOSAR REPEATER .............................................................. 5-1 
5.1 
Repeater Functional Diagram Description ........................................................... 5-1 
5.2 
Electro-L Repeater Operating Modes .................................................................. 5-2 
5.3 
Electro-L Repeater Baseband Spectrum .............................................................. 5-3 
5.4 
Electro-L Repeater Coverage Area ...................................................................... 5-5 
5.5 
Electro-L Repeater Performance Parameters ....................................................... 5-6 
5.5.1 Electro-L SAR Receiver Parameters ........................................................ 5-6 
5.5.2 Electro-L SAR Transmitter Parameters ................................................... 5-8 
5.5.3 Electro-L SAR Antennas .......................................................................... 5-9 
6.
MSG 406 MHz GEOSAR REPEATER ........................................................... 6-1 
6.1 
MSG Repeater Functional Description ................................................................ 6-1 
6.2 
MSG Repeater Operating Modes ......................................................................... 6-2 
6.3 
MSG Repeater Spectrum Characteristics ............................................................. 6-2 
6.3 
MSG Repeater Coverage Area ............................................................................. 6-5 
6.4 
MSG Repeater Performance Parameters .............................................................. 6-5 
6.5 
MSG SAR Antennas ............................................................................................ 6-6 
6.5.1 MSG SAR Receive Antenna .................................................................... 6-7 
6.5.2 MSG SAR Transmit Antenna .................................................................. 6-7 
7.
LOUCH-5A GEOSAR REPEATER ................................................................ 7-1 
7.1 
Louch-5A Repeater Functional Description ........................................................ 7-1 
7.2 
Louch-5A Repeater Operating Modes ................................................................. 7-1 
7.3 
Louch-5A Spectrum Characteristics .................................................................... 7-1 
7.4 
Louch-5A Coverage Area .................................................................................... 7-2 
7.5 
Louch-5A Repeater Performance Characteristics ................................................ 7-2 
7.6 
Louch-5A SAR Antennas ..................................................................................... 7-4 
8.
MTG 406 MHZ GEOSAR REPEATER .......................................................... 8-1 
8.1 
MTG Repeater Functional Description ................................................................ 8-1 
8.2 
MTG Repeater Operating Modes ......................................................................... 8-1 
8.3 
MTG Repeater Spectrum Characteristics ............................................................. 8-2 
8.4 
MTG Repeater Coverage Area ............................................................................. 8-4 
8.5 
MTG Repeater Performance Parameters .............................................................. 8-4 
8.6 
MTG SAR Antennas ............................................................................................ 8-4 


LIST OF FIGURES 
 
Figure 2-1: GEOSAR Payload Functional Diagram .................................................................... 2-2 
Figure 3-1: GOES-15 and before Search and Rescue Repeater  Functional Diagram ................ 3-1 
Figure 3-2: GOES-16-17 Repeater Block Diagram ..................................................................... 3-2 
Figure 3-3: SAR Part of SAR/DCPR Receiver Block Diagram .................................................. 3-3 
Figure 3-4: GOES (15 and Earlier) L-Band Transmitter Output Spectral Occupancy ................ 3-5 
Figure 3-5: For all GOES up to GOES-15: Narrow Band Baseband Spectrum .......................... 3-5 
Figure 3-6: GOES (All) Wide Band Baseband Spectrum ........................................................... 3-6 
Figure 3-7: GOES-16 Downlink Spectrum .................................................................................. 3-7 
Figure 3-8: GOES-E and GOES-W 0o Elevation Coverage Contours ......................................... 3-8 
Figure 3-9: GOES Through GOES-15 Receive Antenna Pattern at 406.05 MHz ..................... 3-11 
Figure 3-10: GOES Through GOES-15 Transmit Antenna Pattern at 1544.5 MHz ................. 3-12 
Figure 3-11: Typical GOES-16 and GOES-17 Receive Antenna Pattern at 406 MHz ............. 3-12 
Figure 3-12: Typical GOES-16 and 17 SAR Transmit antenna measured at 1544 MHz .......... 3-13 
Figure 4-1: INSAT/GSAT SAR / DRT Repeater Functional Block Diagram ............................. 4-1 
Figure 4-2: INSAT Transmitter Output Spectral Occupancy with No Test Signal ..................... 4-3 
Figure 4-3: GSAT Transmitter Output Spectral Occupancy with No Test Signal ...................... 4-3 
Figure 4-4: INSAT-3D 0-Degree Elevation Angle ...................................................................... 4-4 
Figure 4-5: INSAT-3DR 0-Degree Elevation Angle ................................................................... 4-4 
Figure 4-6: GSAT-17 0-Degree Elevation Angle ........................................................................ 4-5 
Figure 4-7: INSAT-3DS 0-Degree Elevation Angle ................................................................... 4-5 
Figure 4-8: INSAT-3D SASR 406.05 MHz Receive Antenna Contour Pattern .......................... 4-7 
Figure 4-9: INSAT-3DR SASR 406.05 MHz Receive Antenna Contour Pattern ....................... 4-7 
Figure 4-10: GSAT-17 SAR 406.05 MHz Receive Antenna Contour Pattern ............................ 4-8 
Figure 4-11: INSAT-3DS SASR 406.05 MHz Receive Antenna Contour Pattern ..................... 4-8 
Figure 4-12: INSAT-3D Transmit Antenna Contour Pattern ...................................................... 4-9 
Figure 4-13: INSAT-3DR Transmit Antenna Contour Pattern .................................................... 4-9 
Figure 4-14: GSAT-17 Transmit Antenna Contour Pattern ...................................................... 4-10 
Figure 4-15: INSAT-3DS Transmit Antenna Contour Pattern .................................................. 4-10 
Figure 5-1: Electro-L SAR Functional Diagram (Linear Phase Modulation Repeater) .............. 5-2 
Figure 5-2: Electro-L SAR Functional Diagram (Frequency Translation Repeater) .................. 5-3 
Figure 5-3: Spectrum Occupancy of Downlink Signal in WB Mode Spanned 300 kHz Around 
1544.5 MHz .......................................................................................................... 5-4 
Figure 5-4: Spectrum Occupancy of Downlink Signal in NB Mode Spanned 1 MHz Around 1544.5 
MHz ...................................................................................................................... 5-4 
Figure 5-5: Spectrum Occupancy of Downlink Signal Centred at 1544.5 MHz.  Electro-L No.4 5-

Figure 5-6: Electro-L 0o Elevation Angle Footprint (Electro- L No 2, 3 and 4) ......................... 5-5 
Figure 5-7: Electro-L SAR Receiver Bandpass Filter Amplitude-Frequency Response (Linear 
Phase Modulation Repeater NB Mode) ............................................................... 5-7 
Figure 5-8: Electro-L SAR Receiver Bandpass Filter Amplitude-Frequency Response (Linear 
Phase Modulation Repeater WB Mode) ............................................................... 5-7 


Figure 5-9: Electro-L SAR Receiver Bandpass Filter Amplitude-Frequency Response (Frequency 
Translation Repeater) ........................................................................................... 5-8 
Figure 6-1: MSG Search and Rescue Repeater Functional Diagram .......................................... 6-1 
Figure 6-2: MSG L-Band Transmitter Output Spectral Occupancy ............................................ 6-2 
Figure 6-3: Measured Pass-Band of MSG Transponder .............................................................. 6-3 
Figure 6-4: MSG Transmitter LO Phase Noise Spectrum Plot .................................................... 6-4 
Figure 6-5: MSG 5 o Elevation Angle Coverage Contour ........................................................... 6-5 
Figure 6-6: MSG SAR Receive Antenna Pattern ........................................................................ 6-8 
Figure 6-7: MSG SAR Transmit Antenna Pattern ....................................................................... 6-9 
Figure 7-1: Louch-5A Combined SAR and EDDN Transponder ................................................ 7-1 
Figure 7-2: Louch-5A Transmitter Spectrum Occupancy ........................................................... 7-2 
Figure 7-3: Louch-5A Coverage Zones for 0, 5 and 10 Degrees of Elevation Angle ................. 7-3 
Figure 7-4: Louch-5A Receive Antenna Pattern at 406.05 MHz ................................................ 7-5 
Figure 7-5: Louch-5A Transmit Antenna Pattern at 1544.5 MHz ............................................... 7-5 
Figure 8-1: MTG SAR Repeater Functional Block Diagram ...................................................... 8-1 
Figure 8-2: MTG Repeater Output Spectrum (Narrowband Mode) ............................................ 8-2 
Figure 8-3: MTG Repeater Output Spectrum (Wideband Mode) ................................................ 8-2 
Figure 8-4: MTG SAR Repeater Narrowband Filter Performance .............................................. 8-3 
Figure 8-5: MTG SAR Repeater Wideband Filter Performance ................................................. 8-3 
Figure 8-6: MTG UHF-Band Antenna Co-Polar Amplitude Pattern (Antenna Gain in dB Relative 
to the Peak Gain of 14.2 dBi; Red Circle Shows the Earth) ................................. 8-5 
Figure 8-7: MTG L-Band Antenna Co-Polar Amplitude Pattern (Antenna Gain in dB Relative to 
the Peak Gain of 14.2 dBi; Red Circle Shows the Earth) ..................................... 8-5 
 
 
LIST OF TABLES 
 
Table 3.1: GOES Repeater Operating Modes .............................................................................. 3-4 
Table 3.2: GOES SAR Receiver Parameters ............................................................................... 3-9 
Table 3.3: GOES SAR Transmitter Parameters ......................................................................... 3-10 
Table 4.1: INSAT/GSAT Repeater Operating Modes ................................................................. 4-2 
Table 4.2: INSAT/GSAT Repeater Performance Parameters ...................................................... 4-6 
Table 5.1: Electro-L Repeater Operating Modes ......................................................................... 5-2 
Table 5.2: Electro-L SAR Receiver Parameters .......................................................................... 5-6 
Table 5.3: Electro-L SAR Transmitter Parameters ...................................................................... 5-8 
Table 6.1: MSG Transmitter LO Phase Noise ............................................................................. 6-4 
Table 6.2: MSG SAR Repeater Performance Parameters ........................................................... 6-6 
Table 7.1: Louch-5A SAR Receiver Parameters ......................................................................... 7-3 
Table 7.2: Louch-5A SAR Transmitter Parameters ..................................................................... 7-4 
Table 8.1: MTG SAR Repeater Performance Parameters ........................................................... 8-4 
 
 
 


 
1-1 
 
 

1. 
INTRODUCTION 
1.1 
Overview 
The Cospas-Sarsat Space Segment consists of satellites in low earth orbit (LEO) equipped with 
search and rescue (SAR) instruments.  The LEO satellites are complemented by satellites in 
geostationary earth orbit (GEO) with their respective SAR instruments.  These geostationary 
search and rescue (GEOSAR) instruments are currently flown on USA and Indian spacecraft, and 
it is anticipated that they will also be flown on Russian and EUMETSAT spacecraft in the near 
future.  The 406 MHz data received from these instruments are processed by Cospas-Sarsat Ground 
Segment equipment and provided to SAR agencies.  This document provides a description of the 
GEOSAR instruments carried on board these spacecraft.  The description of the Cospas-Sarsat 
LEO Space Segment is provided in document C/S T.003. 
1.2 
Purpose 
The purpose of this document is to describe the functionality and performance parameters for each 
GEOSAR instrument.  The document is intended to be used to ensure the necessary compatibility 
for the 406 MHz beacon to satellite uplink and compatibility for the satellite to geostationary local 
user terminal (GEOLUT) downlink.  The document is not intended for use as a specification for 
procurement of hardware for GEOSAR satellite repeaters. 
1.3 
Scope 
This document presents a technical description of the GEOSAR repeaters used in the Cospas-
Sarsat system.  Section 2 provides a general overview of the GEOSAR repeater function.  Sections 
3, 4, 5, and 6 provide descriptions of the repeaters on the USA, Russian, Indian, and EUMETSAT 
satellites. 
1.4 
Reference Documents 
The following documents contain useful information to the understanding of this document. 
 
 
C/S T.001, Specification for Cospas-Sarsat 406 MHz Distress Beacons 
 
C/S T.003, Description of the Payloads used in the Cospas-Sarsat LEOSAR System 
 
C/S T.009, Cospas-Sarsat GEOLUT Specification and Design Guidelines 
 
C/S T.010, Cospas-Sarsat GEOLUT Commissioning Standard 
 
C/S G.003, Introduction to the Cospas-Sarsat System 
 
C/S S.011, Cospas-Sarsat Glossary 


 
1-2 
 
 

- END OF SECTION 1 - 
 


 
2-1 
 
 

2. 
COSPAS-SARSAT PARAMETERS 
The Cospas-Sarsat GEOSAR Space Segment consists of SAR instruments on board satellites in 
geostationary orbit.  The SAR instruments are radio repeaters that receive distress beacon signals 
in the 406 - 406.1 MHz band and relay these signals to GEOLUTs for processing beacon 
identification and associated data.  A description of the Cospas-Sarsat beacon signal parameters 
and data protocols is provided in reference documents C/S T.001 and C/S T.018.   The series of 
satellites with GEOSAR instruments currently in use are shown below.  
 
GEOSAR Satellite series 
Country/Organization 
GOES 
USA 
INSAT 
India 
MSG 
EUMETSAT 
MTG 
EUMETSAT 
Electro-L 
Russia 
Louch 
Russia 
 
The detailed list of GEOSAR payloads and their current operational status is available on the 
Cospas-Sarsat 
website 
at 
https://www.cospas-sarsat.int/en/system/space-segment-status-
pro/current-space-segment-status-and-sar-payloads-pro. 
 
2.1 
406 MHz GEOSAR Payload Functional Description 
A functional diagram of SAR instruments on GEOSAR spacecraft is shown in Figure 2.1. The 
GEOSAR instruments were independently developed and integrated into spacecraft that have 
different mission requirements. This has resulted in differences in repeater designs that affect the 
output signal as described in sections 3, 4, 5, 6, 7 and 8. These differences must be considered in 
developing a GEOLUT. 
 
The GEOSAR repeater receives 406 MHz beacon signals within the field of view of the 406 MHz 
receive antenna beam. The beacon signals are processed by the repeater and transmitted on the 
downlink signal for reception by a GEOLUT. The downlink center frequency and antenna pattern 
characteristics vary among the different repeater implementations as described in subsequent 
sections of this document. 
 
 


2-2

Figure 2-1: GEOSAR Payload Functional Diagram 
2.2 
GEOSAR Orbit Summary 
Each of the GEOSAR satellites with operational payloads in a geostationary orbit with an orbital 
period of 24 hours with nominal parameters available on the Cospas-Sarsat website at 
https://www.cospas-sarsat.int/en/system/space-segment-status-pro/current-space-segment-status-
and-sar-payloads-pro. 
2.3 
GEOSAR System Coverage 
The 406 MHz coverage area for the on-orbit operational GEOSAR payloads (using a nominal 
GEOSAR 5-degree elevation) is available on the Cospas-Sarsat website at https://www.cospas-
sarsat.int/en/system/detailed-leosar-geosar-system-description/geosar-satellite-coverage. 
- END OF SECTION 2 -


 
3-1 
 
 

3. 
COSPAS-SARSAT REPEATERS 
3.1 
GOES Repeater Functional Description 
3.1.1 
GOES 15 and Before 
A functional diagram of the GOES SAR repeater is shown in Figure 3.1.  The repeater is 
redundantly configured and consists of the following units: 
 
 two 406 MHz low noise amplifiers (shared with another satellite subsystem); 
 two dual-conversion 406 MHz receivers; 
 two 3-watt phase modulated L-Band transmitters; 
 one 406 MHz receive antenna and one 1544.5 MHz transmit antenna; and 
 command and telemetry points interfaced with the spacecraft telemetry and 
command subsystem. 
 
 
Figure 3-1: GOES-15 and before Search and Rescue Repeater  
Functional Diagram 
 
The 406 MHz signals from Cospas-Sarsat distress beacons are received on the UHF antenna 
and fed through the antenna diplexer and switch to a low noise amplifier in one of the 
redundant pair of Data Collection Platform Repeaters (DCPR).  The DCPR low noise 
amplifiers are used as part of the SAR implementation to accommodate circuit efficiency on 


 
3-2 
 
 

the spacecraft.  The low noise amplifier outputs are connected to the redundant pair of SAR 
receivers.  The signal applied to the selected receiver is down-converted for bandpass filtering 
in accordance with one of two commandable bandwidth modes; a narrow band mode of 
20 kHz or a wide band mode of 80 kHz.  The filtered output signal is further down-converted 
to near baseband and fed through amplifiers to the SAR transmitter.  The overall gain of the 
SAR receiver can be command selected into a fixed gain or Automatic Level Control (ALC) 
mode.  
 
The outputs of the receivers are provided to the redundant pair of SAR transmitters.  The 
selected SAR transmitter phase modulates the signal, multiplies the signal to 1544.5 MHz, 
and amplifies the modulated carrier to 3 Watts.  The phase modulated signal has the nominal 
modulation index set such that the carrier suppression is 3 dB with the receiver in the ALC 
mode or with the receiver in the fixed gain mode operating with two nominal beacon signals 
plus the noise.  A baseband limiter restricts the modulation index from exceeding 2 radians.  
The transmitter output is applied through a 4 MHz bandwidth filter to the helical antenna and 
radiated with an effective radiated isotropic power (EIRP) of +15.0 dBW. 
 
3.1.2 
GOES 16 and Later 
The GOES-R and GOES-S (GOES-16 and GOES-17 after launch) repeater is part of the 
SAR/DCPR system. Figure 3.2 shows a high-level view of the repeater and the SAR part of 
the SAR/DCPR receiver. 
 
 
Figure 3-2: GOES-16-17 Repeater Block Diagram 
 
 


 
3-3 
 
 

Figure 3-3: SAR Part of SAR/DCPR Receiver Block Diagram 
 
In the GOES 16-17 series of spacecraft, the SAR repeater is shared with the data Collection 
platform (DCPR) as in previous GOES spacecraft.  There are redundant receivers, a choice 
between fixed gain and ALC modes, and a frequency translation scheme.  Frequency 
translation means that there is no modulator in the SAR receiver and the UHF input signal is 
first frequency translated by a mixer down to 30.55 MHz for filtering and then frequency 
translated via another mixer up to 1544.55 MHz by another LO. Figure 3.3 shows the 2 local 
oscillators with the 1514 MHz oscillator providing low side injection, so the downlink spectra 
is not reversed as it would be if this LO ‘s frequency were higher than the output frequency. 
Notable is a new downlink frequency, 1544.55 MHz as opposed to the usual 1544.50 MHz in 
previous GOES, and a no narrow band mode. This was done to achieve a better G/T and a 
steeper filter skirt for the UHF input which will help in rejecting signals which are close to 
the UHF frequency. The receiver is commandable into a fixe gain mode or an ALC mode, as 
in previous GOES. 
3.2 
GOES Repeater Operating Modes 
The GOES repeater has redundant low noise amplifiers, receivers, and transmitters that can be 
selected to define a complete repeater configuration.  A specific repeater configuration can be 
operated in the modes described in Table 3.1.  GOES-16 and all follow on GOES will have only 
wide band modes. 
 
 


 
3-4 
 
 

Table 3.1: GOES Repeater Operating Modes 
 
Mode 
Band Center 
Frequency 
(MHz) 
GOES spacecraft 
up to GOES-15 
Receiver 3 dB 
Bandwidth (kHz) 
GOES-16 and later 
Receiver 3 dB 
Bandwidth (kHz) 
Narrow Band with ALC 
406.025 

N/A 
Narrow Band Fixed Gain 
406.025 

N/A 
Wide Band with ALC 
406.050 


Wide Band Fixed Gain 
406.050 


3.3 
GOES Repeater Spectrum Characteristics 
3.3.1 
All GOES up to GOES-15 
The spectral occupancy of the transmitted signal with the repeater in the wide band mode is 
shown in Figure 3.4. This output spectrum, which applies the GOES spacecraft up to GOES-
15, therefore, represents the case of maximum spectrum occupancy. The spectrum plot was 
taken at a received intermediate frequency of 44.5 MHz that is equivalent to a transmitted 
frequency of 1544.5 MHz spectrum width. The narrow band spectrum is shown in 
Figure 3.3a. The wide band spectrum is shown in Figure 3.3b. 
 
The baseband spectral characteristics are shown in Figures 3.5 and 3.6.  The received 
406 MHz beacon signals are filtered and translated to a baseband frequency prior to phase 
modulation in the transmitter.  The modulation plan is such that a signal received at 
406.000 MHz becomes zero Hz in the baseband spectrum.  A Cospas-Sarsat beacon received 
at 406.025 MHz will be at 25 kHz in the baseband spectrum.  The 20 kHz and 80 kHz 
bandpass filters control the baseband spectrum width.  The narrow band spectrum is shown 
in Figure 3.5.  The wide band spectrum is shown in Figure 6. 


 
3-5 
 
 

Figure 3-4: GOES (15 and Earlier) L-Band Transmitter Output Spectral Occupancy 
 
 
 
Figure 3-5: For all GOES up to GOES-15: Narrow Band Baseband Spectrum 
 
 
 
 
 


3-6

Figure 3-6: GOES (All) Wide Band Baseband Spectrum 


3-7

3.3.2 
GOES 16 and Later 
Figure 3-7: GOES-16 Downlink Spectrum 
3.4 
GOES Repeater Coverage Area 
The zero-degree elevation angle coverage contour for the GOES-E and two GOES-W satellites is 
shown in Figure 3.4. The receive and transmit antennas are broad beam earth coverage types.  
Therefore, the coverage patterns in Figure 3.8 apply to both the receive and transmit functions. 


 
3-8 
 
 

Figure 3-8: GOES-E and GOES-W 0o Elevation Coverage Contours 
 
3.5 
GOES Repeater Performance Parameters 
3.5.1 
GOES SAR Receiver Parameters 
The receiver parameters are shown in Table 3.2. 
 
 


 
3-9 
 
 

Table 3.2: GOES SAR Receiver Parameters 
 
Parameter 
Unit All GOES up to GOES-15 
Values 
GOES-16 and later 
Values 
Nominal Input Level at Antenna 
dBW 
-173.1 
-173.1 
System Noise Temperature  
(referred to preamp input) 
K 


G/T 
dB/K 
-18.5 
>-15.5  
(-13.3 for GOES-16) 
Receiver Bandpass Characteristic 
Narrow Band Mode  
(relative to 406.025 MHz) 
Wide Band Mode  
(relative to 406.05 MHz) 
 
kHz 
 
 
 
kHz 
 6.0 (1 dB BW) 
 10.0 (3 dB BW) 
 20.0 (20 dB BW) 
 
 30.0 (1 dB BW) 
 40.0 (3 dB BW) 
 50.0 (20 dB BW) 
 
No narrow band mode 
 
 
>80 (1 dB BW) 
<100 (3 dB BW) 
<130 (20 dB BW) 
<180 (40 dB BW) 
<230 (50 dB BW) 
Dynamic Range 
dB 
 15 
 
Group Delay  
(over 4 kHz) 
s/kHz 
 13 
 
Image Rejection 
dB 

70 @ ±21.4 MHz 
AGC Time Constant 
ms 
 40 
  
Frequency Stability 
Frequency Conversion 
Oscillators (over 0.25 s) 
 
N/A 
 
 1 x 10-9 
 
 
Note 1: 
Nominal input level at antenna from 5 Watt beacon located at 45° elevation angle to 
the satellite. Includes 4.1 dB polarization loss. 
 
 


 
3-10 
 
 

3.5.2 
 
GOES SAR Transmitter Parameters 
 
The transmitter parameters are shown in Table 3.3. 
 
Table 3.3: GOES SAR Transmitter Parameters 
 
 
Parameter 
Unit 
All GOES up to 
GOES-15 Values 
GOES-16 and later 
Values 
Centre Frequency 
MHz 
1544.5 
1544.55 
Output Power of Transmitter 
W 
3.0 
7.0 
Repeater EIRP 
dBW 
+ 15.0 
+15.0  
(+17.3 for GOES-16) 
Phase Jitter (in 50 Hz bandwidth) 
deg. (rms) 
 10 
 
Modulation Type 
type 
Linear Phase 
None: frequency 
translation 
Transmitter  
Nominal Modulation Index 
 Modulation Index Limit 
radians 
peak 
1.0 
2.0 
N/A 
Frequency Stability of downlink carrier 
N/A 
 2.5 x 10-6 
 
Amplitude Ripple (over any 24-hour 
period) 
dB 
 1 
 1 
Linearity 
dB 
see note 1 
30 dB below desired 
signal levels 
 
Note 1:  Fixed Gain Mode - Two equal test tones each at 2 dB above the receiver noise 
applied to the receiver input will not produce intermodulation products within the 
transponder bandwidth greater than 20 dB below the test tone output level. 
 
ALC Mode - Two equal test tones each at 7 dB above the receiver noise applied to 
the receiver input will not produce intermodulation products within the transponder 
bandwidth greater than 30 dB below the test tone output level. 
 
3.5.3 
GOES SAR Antennas 
The relative gain pattern for the GOES SAR receive antenna is shown in Figure 3.9 for GOES 
up to GOES-15 and in Figure 3.11 for GOES-16 and later. The antenna is right hand circular 
polarized (RHCP) with an on-axis gain of 10 dB for GOES spacecraft up to GOES-15 and 
about 14 dB for GOES-16.  
 


 
3-11 
 
 

For GOES spacecraft up to GOES-15, the receive line loss between the antenna terminal and 
the low noise preamplifier is 1.9 dB. Therefore, the effective gain relative to the preamplifer 
input is 8.1 dB. The receive antenna has a maximum axial ratio of 3 dB. 
 
The relative gain pattern for the GOES through GOES-15 SAR transmit antenna is shown in 
Figure 3.10. The antenna is RHCP with an on-axis gain of 12.3 dB. The transmit line loss 
between the power amplifier and the antenna terminal is 1.7 dB. Therefore, the effective gain 
relative to the power amplifier output is 10.6 dB. The transmit antenna has a maximum axial 
ratio of 3 dB.  
 
Figure 3-9: GOES Through GOES-15 Receive Antenna Pattern at 406.05 MHz 


 
3-12 
 
 

Figure 3-10: GOES Through GOES-15 Transmit Antenna Pattern at 1544.5 MHz 
 
 
 
Figure 3-11: Typical GOES-16 and GOES-17 Receive Antenna Pattern at 406 MHz 
 


 
3-13 
 
 

Figure 3-12: Typical GOES-16 and 17 SAR Transmit antenna measured at 1544 MHz 
 
For the GOES-16 and 17 transmit plot, Figure 3.12, the blue curve is the correct polarization 
(RHCP) and the red curve is cross polarization (LHCP) plots. 
 
 
 
- END OF SECTION 3 - 
 
 


 
4-1 
 
 

4. 
INSAT/GSAT 406 MHZ GEOSAR REPEATER 
4.1 
INSAT/GSAT Repeater Functional Description 
SAR instruments are included on the INSAT-3D, INSAT-3DR, GSAT-17 and INSAT-3DS 
satellites.  On each of these satellites the SAR payloads share some common circuitry with the 
Data Relay Transponder (DRT) meteorological instruments.  A functional diagram of the 
INSAT/GSAT SAR payloads is provided at Figure 4.1. 
 
Figure 4-1: INSAT/GSAT SAR / DRT Repeater Functional Block Diagram 
 
406.05 MHz signals from Cospas-Sarsat distress beacon within the coverage area of the SAR 
receive antenna are fed to a pre-select helical band pass filter which helps suppress out-of-band 
interference.  The filtered signal is passed to a low noise amplifier (LNA) to achieve the required 
input noise figure.  The signal is first down converted to 73.35 MHz, then passed through a crystal 
bandpass filter.  This signal is further down converted, such that an uplink signal at 406.05 MHz 
would appear at 100 kHz.  The resulting signal is passed to a transistorized limiter circuit and to a 
low pass filter.  The filtered signal is phase modulated and multiplied to achieve a modulation 
index of ±1 radian at 71.0 MHz. 
 
The main functions of the phase modulator are to: 
• Reduce noise in the down link signal; and 
• Provide a continuous down link carrier for LUT tracking receivers. 
 
 
 
 
 
SAR Receiver 
 
15WSSPA 
Filter
 
 
 
0.9m Ext C BAND 
DRT: 402.675 
MHz
 
 
HYB
 
PSF 
PSF 
SHORTBACK FIRE 1m 
ANTENNA 
SAS&R: 
406.05 MHz
 
DRT/SAS&R 
Receiver
LHCP
 
 
RHCP
 
SW     TR SW        
 
DRT: 4503.385 MHz
SAS&R: 4504.2 MHz


 
4-2 
 
 

The output signal form the modulator is filtered, combined with the DRT IF signal (70.05 MHz), 
up-converted to 4504.2 MHz and applied to a 15-Watt solid state power amplifier (SSPA operating 
at 3 dB out back off at 0 dB BOA settings). The composite DRT / SAR transponder signal is passed 
to an extended C band multiplexer (MUX).  Finally the signal is routed to an extended C band 
antenna which provides an EIRP of 4 dBW for INSAT-3DS (minimum). 
4.2 
INSAT/GSAT Repeater Operating Modes 
Each INSAT repeater has a redundant receiver and a redundant transmitter that can be selected to 
define a complete repeater configuration.  A specific repeater configuration can be operated in the 
modes described in Table 4.1. 
Table 4.1: INSAT/GSAT Repeater Operating Modes 
 
Mode 
Band Center 
Frequency (MHz) 
Receiver 1 dB 
Bandwidth (kHz) 
Wide Band 
406.050 

4.3 
INSAT/GSAT Repeater Spectrum Characteristics 
The spectral occupancy of the transmitted signal with the repeater in a wide band mode is shown 
in Figure 4.2 and Figure 4.3. This output spectrum, therefore, represents the case of maximum 
spectrum occupancy. 
 
The received 406.05 MHz beacon signals are filtered and translated to a baseband frequency prior 
to phase modulation in the transmitter.  The wide band mode (80 kHz bandwidth) frequency plan 
is such that a Cospas-Sarsat beacon signal received at 406.05 MHz becomes 100 kHz in the 
baseband spectrum. 
 


 
4-3 
 
 

Figure 4-2: INSAT Transmitter Output Spectral Occupancy with No Test Signal 
 
 
 
Figure 4-3: GSAT Transmitter Output Spectral Occupancy with No Test Signal 
 


 
4-4 
 
 

4.4 
INSAT/GSAT Repeater Coverage Area 
The zero-degree elevation angle coverage contours for the INSAT-3D, INSAT-3DR, GSAT-17 
and INSA-3DS are shown in Figure 4.4, Figure 4.5, Figure 4.6 and Figure 4.7, respectively.  The 
receive antennas are broad beam earth coverage types.  The downlink antennas are directive beams 
that can be received in the Indian region. 
 
 
Figure 4-4: INSAT-3D 0-Degree Elevation Angle 
 
 
 
 
Figure 4-5: INSAT-3DR 0-Degree Elevation Angle 
 


4-5

Figure 4-6: GSAT-17 0-Degree Elevation Angle 
Figure 4-7: INSAT-3DS 0-Degree Elevation Angle 


 
4-6 
 
 

4.5 
INSAT/GSAT Repeater Performance Parameters 
 
The INSAT SAR repeater performance parameters for both INSAT-3D, INSAT-3DR, G-SAT-17 
and INSAT-3DS are provided in Table 4.2. 
 
Table 4.2: INSAT/GSAT Repeater Performance Parameters 
 
Parameter 
Unit 
Specification 
Receiver Band Pass Characteristics 
 
Wide band mode center frequency 
 
Wide band mode bandwidth   
 
MHz 
kHz 
 
406.05 

Antenna Type (UHF) 
N/A 
Short back fire (SBF) 
Rx Antenna Polarization 
N/A 
RHCP 
SBF Antenna Gain 
dBi 

UHF receive antenna axial ratio 
dB 
2.0 
Receive coverage 
N/A 
Global 
Receive Gain to Noise Temp Ratio (G/T) 
dB/K 
-19.0 
Nominal Input Level 
dBW 

Dynamic Range 
dB 

Spurious outside the transmit band in any 4 kHz Band 
dBW 
< -60  
Gain Stability (over operating life) 
dB PP 
4.0 
Transmit Center frequency 
MHz 
INSAT-3D   : 4507.0 
INSAT-3DR : 4504.2 
GSAT-17     : 4504.2 
INSAT-3DS : 4504.2 
Tx Antenna Polarization 
N/A 
Linear V 
Transmit Antenna Input 
dBm 
7.5 
Transmit Antenna Gain (EOC) 
dB 
26.5 
EIRP (EOC at end of life) 
dBW 

Tx Antenna Beam Coverage 
N/A 
INDIA Mainland 
SAR Signal Modulation 
N/A 
Phase modulation 
Modulation Index (Nominal) 
Radian 
1.0 ± 0.2 
Overall Frequency translation error (Over lifetime) 
PPM 
± 8.0 
4.6 
INSAT/GSAT SAR Antennas 
The SAR receive antenna (SBF type) for INSAT/GSAT satellites provide global coverage. The 
antenna is right hand circular polarized (RHCP) with an edge of coverage (EOC) gain of 12.2 dB. 
The pattern for INSAT-3D is shown in Figure 4.8, for INSAT-3DR in Figure 4.9, for GSAT-17 in 
Figure 4.10 and for INSAT-3DS in Figure 4.11. The receive antenna has a maximum axial ratio 
of 2 dB. 
 


 
4-7 
 
 

Figure 4-8: INSAT-3D SASR 406.05 MHz Receive Antenna Contour Pattern 
 
 
Figure 4-9: INSAT-3DR SASR 406.05 MHz Receive Antenna Contour Pattern 


4-8

Figure 4-10: GSAT-17 SAR 406.05 MHz Receive Antenna Contour Pattern 
Figure 4-11: INSAT-3DS SASR 406.05 MHz Receive Antenna Contour Pattern 


4-9

The INSAT/GSAT extended C-band transmit antenna is a directive antenna that provides coverage 
for the Indian region.  The pattern is shown in Figure 4.12 for INSAT-3D, in Figure 4.13 for 
INSAT 3-DR, in Figure 4.14 for GSAT-17 and in Figure 4.15 for INSAT-3DS. The antenna is 
vertically polarized with an EOC gain of 26.0 dB. 
Figure 4-12: INSAT-3D Transmit Antenna Contour Pattern 
Figure 4-13: INSAT-3DR Transmit Antenna Contour Pattern 


 
4-10 
 
 

Figure 4-14: GSAT-17 Transmit Antenna Contour Pattern 
 
 
Figure 4-15: INSAT-3DS Transmit Antenna Contour Pattern 
 
 
 
– END OF SECTION 4 – 


 
5-1 
 
 

5. 
ELECTRO-L GEOSAR REPEATER 
5.1 
Repeater Functional Diagram Description 
A functional diagram of the Electro-L SAR repeater is shown in Figure 5.1 and Figure 5.2. The 
repeater is redundantly configured and consists of the following units: 
• two 406 MHz low-noise amplifiers (shared with another satellite subsystem); 
• two dual conversion 406 MHz receivers (down converter, up converter); 
• two 4-Watt 1.5 GHz transmitters; 
• one 406 MHz receive antenna; and 
• one 1544.5 MHz transmit antenna. 
There are two generations of Electro-L SAR repeaters: with linear phase modulation (Electro-L 
No. 1, 2 and 3) and frequency translation (“bent-pipe”) transponder (Electro-L No. 4 and onwards). 
 
5.1.1 ELECTRO-L Linear Phase Modulation Repeaters (Electro- L No. 1, 2 and 3) 
406 MHz signals from 406 MHz beacons are received by the antenna and fed through the diplexer 
and switch to a low-noise amplifier.  The low-noise amplifier output is connected to the SAR 
receiver.  The signal is down-converted for bandpass filtering in accordance with one of two 
commandable band with modes; a narrow band mode of 20 kHz or a wide band mode of 80 kHz. 
 
The filtered output signal is further down-converted to the near baseband and fed through 
amplifiers to the SAR transmitter.  The overall gain of the SAR receiver is selected into a fixed 
gain mode only. 
 
The SAR transmitter linear phase modulates the signal 1544.5 MHz and amplifies the modulated 
carrier to 4 Watts.  The phase-modulated signal has the nominal modulation index set to 0.7 radian 
(rms).  A baseband limiter restricts the modulation index from exceeding 2 radians.  The 
transmitter output is applied through a 4 MHz bandwidth filter to antenna.  
 
5.1.2 ELECTRO-L Frequency Translation Repeaters (Electro-L No.4 and 
Onwards) 
The SAR repeater is based on frequency translation type transponder with no frequency inversion. 
The 406 MHz signals from beacons are received by the antenna and fed through the diplexer and 
switch to a low-noise amplifier. The low-noise amplifier output is connected to the SAR receiver.  
The signal is down-converted for bandpass filtering with only wide band mode of 80 kHz. Repeater 
gain is self-regulated by Automatic Gain control (AGC). The repeater gain is automatically 
adjusted to obtain a power of 4 W at the output of the SAR transponder. 


 
5-2 
 
 

5.2 
Electro-L Repeater Operating Modes 
A specific repeater configuration can be operated in the modes described in Table 5.1. 
 
Table 5.1: Electro-L Repeater Operating Modes 
 
Mode 
Band Center Frequency 
(MHz) 
Receiver 3 dB Bandwidth 
(kHz) 
ELECTRO-L (No.1, No.2, No.3) 
Narrow Band with Fixed Gain 
406.025 

Wide Band with Fixed Gain 
406.050 

ELECTRO-L (No.4 and onwards) 
 
 
 
Wide Band with Automatic Gain Control 
406.050 

1544.5 MHz
406 MHz
LEGEND
FS1...FS3 - frequency synthesizers; 
S - switch of the quartz filters;
QF - quartz filter;
LPM - linear phase modulator;
ATT - attenuator;
PSS1...PSS2  - power supply sources
Ant1  - directive antenna of the receiving channel;
Ant2  - directive antenna of the transmission channel;
LNA - low-noise amplifier;
A  - amplifier;
F1...F4 - frequency filters;
M1, M2 - frequency mixers
LNA
A
F2
M1
FS1
A
Down converter
Input unit
F=(406.05±0.05) MHz
Fо=10 MHz
Fg=380 MHz
F=26.05 MHz
Power
amplifier
PSS3
PSS1
F4
F1
Ant1
Ant2
A
S
QF
20kHz
QF
80кHz
M2
FS2
A
A
LPM
A
F3
ATT
FS3
Up converter and LFM 
Fo=10 MHz
Fo=10 MHz
PSS2
A
Fg=26 MHz
Fg=1544.5 MHz
0.05 MHz
 
Figure 5-1: Electro-L SAR Functional Diagram (Linear Phase Modulation Repeater) 
 
 


 
5-3 
 
 

LEGEND 
 
 
Ant1 - directive antenna of the receiving channel;  
Ant2 - directive antenna of the transmission channel;  
LNA - low-noise amplifier; 
A - amplifier; 
F1...F4 - frequency filters; M1, M2 - frequency mixers  
FS1,FS2 - frequency synthesizers;  
QF - quartz filter; 
ATT - attenuator; 
PSS1...PSS3 - power supply sources 
 
Figure 5-2: Electro-L SAR Functional Diagram (Frequency Translation Repeater) 
 
5.3 
Electro-L Repeater Baseband Spectrum 
5.3.1 ELECTRO-L Linear Phase Modulation Repeaters (Electro- L No. 1, 2 
and 3) 
 
The received 406 MHz signals are filtered and translated to a baseband frequency prior to phase 
modulation in the transmitter.  The modulation plan is such that a beacon received at the 
406.025 MHz will be at 25 kHz in baseband spectrum.  The 20 kHz and 80 kHz filters control the 
baseband spectrum width.  
 
The Electro-L SAR downlink spectrum occupancies in WB and NB modes are depicted in 
Figures 5.3 and 5.4 respectively. Note that out-of-band emissions are not greater than 30 dB below 
the carrier frequency level. 


 
5-4 
 
 

Figure 5-3: Spectrum Occupancy of Downlink Signal in WB Mode 
Spanned 300 kHz Around 1544.5 MHz 
 
 
Figure 5-4: Spectrum Occupancy of Downlink Signal in NB Mode 
Spanned 1 MHz Around 1544.5 MHz 
 
 
5.3.2 ELECTRO-L Frequency Translation Repeaters (Electro-L No.4 and 
Onwards) 
The Electro-L SAR frequency translation repeater can operate in one gain and one bandwidth 
mode. The nominal SAR downlink spectrum occupancy is depicted in Figure 5.5. 
 


5-5

Figure 5-5: Spectrum Occupancy of Downlink Signal Centred at 1544.5 MHz. 
Electro-L No.4 
5.4 
Electro-L Repeater Coverage Area 
The 0-degree elevation angle coverage contour for the Electro-L satellite are provided in 
Figure 5.6.  The receive and transmit antennas are broad beam earth coverage types. Therefore, 
the coverage patterns in Figure 5.6 apply to both receive and transmit functions. 
Figure 5-6: Electro-L 0o Elevation Angle Footprint 
(Electro- L No 2, 3 and 4) 


 
5-6 
 
 

5.5 
Electro-L Repeater Performance Parameters 
5.5.1 
Electro-L SAR Receiver Parameters 
The receiver parameters are shown in Table 5.2. 
 
Table 5.2: Electro-L SAR Receiver Parameters 
 
No. 
Parameter 
Unit 
Values 
1. 
Nominal input level at Antenna 
dBW 

2. 
System Noise Temperature (referred to LNA)   
K 

3. 
G/Т 
dB/K 
-16.5 (see Note) 
4. 
Receiver Bandpass Characteristic 
Linear phase modulation repeater: 
Narrow Band Mode (relat. to 406.025) 
 
 
Wide Band Mode (relat. to 406.050) 
 
 
Bent-pipe repeater: 
Wide Band Mode (relat. to 406.050) 
 
For more information see Figures 5.7, 5.8 and 5.9. 
 
 
kHz 
 
 
kHz 
 
 
kHz 
 
 
33 (-1 dB) 
39 (-3 dB) 
64 (-20 dB) 
78 (-1 dB) 
138 (-3 dB) 
 
96 (-3 dB) 
120 (-10 dB) 
5. 
Dynamic Range 
kHz dB  
≤ 15 
6. 
Group Delay (over 4 kHz) 
s 
≤ 13 
7. 
Image Rejection  
dB  

8. 
Frequency Stability for 24h/10 years 
dB  
± 2.5 x 10-6 
Note: For Electro-L No. 2 the G/T value was measured at -21.9 dB/K. 


 
5-7 
 
 

Figure 5-7: Electro-L SAR Receiver Bandpass Filter Amplitude-Frequency Response 
(Linear Phase Modulation Repeater NB Mode) 
 
 
 
Figure 5-8: Electro-L SAR Receiver Bandpass Filter Amplitude-Frequency Response 
(Linear Phase Modulation Repeater WB Mode) 
 


 
5-8 
 
 

Figure 5-9: Electro-L SAR Receiver Bandpass Filter Amplitude-Frequency Response 
(Frequency Translation Repeater) 
 
5.5.2 
Electro-L SAR Transmitter Parameters 
The transmitter parameters are shown in Table 5.3. 
 
Table 5.3: Electro-L SAR Transmitter Parameters 
 
No. 
Parameter 
Unit 
Values 
 
No. 1,2 and 3 
No. 4 and 
onwards 
No.  Centre Frequency 
МHz 
1544.5 
 
2. 
Output Power of Transmitter 
dBW 
6.0 
 
3. 
Repeater EIRP 
dBW 
20.1 

4. 
Phase Jitter (in 50 Hz bandwidth) 
deg 
≤ 10 (r.m.s.) 
≤ 10 (r.m.s.) 
5. 
Modulation Type 
 
Linear Phase  
- 
6. 
Nominal Modulation Index 
radian 
0.7 (rms) 
- 
7. 
Modulation Index Limit  
radian  
2.0 
- 
8. 
Frequency Stability  
 
±2.5 x 10-7 
9. 
Amplitude Ripple (over any 24 hour)  
dB 
±1 
±1.7 
10. 
Linearity  
 
See Note 1 
 
 
Note 1:  
Fixed gain mode: Two equal test tones each at 2 dB above the receiver noise applied to the 
receive input will not produce intermodulation products within the transponder bandwidth 
greater than 20 dB below the test tone output level.   


 
5-9 
 
 

AGC Mode: Two equal test tones each at 7 dB above the receiver noise applied to the receiver 
input will not produce intermodulation products within the transponder bandwidth greater 
than 18 dB below the test tone output level. 
 
5.5.3 
Electro-L SAR Antennas 
The SAR receive antenna is right-hand circularly polarized (RHCP) with an on-axis gain of 
15 dB including line loss.  The receive antenna has a maximum axial ratio of 3 dB. 
 
The SAR transmit antenna is also LHCP with an on-axis gain of 12 dB (±9o beamwidth) 
including line loss.  The transmit antenna has a maximum axial ratio of 3 dB. 
 
 
 
– END OF SECTION 5 – 
 


6-1

6.
MSG 406 MHZ GEOSAR REPEATER
6.1 
MSG Repeater Functional Description 
A functional block diagram of the overall MSG telecommunications payload, including the SAR 
transponder is shown in Figure 6.1.  The SAR transponder comprises the following: 
A UHF receive antenna which is made up of an array of 16 crossed dipoles located close 
to the periphery of the main satellite drum.  The dipoles of this array are electronically 
switched in order to form an electronically de-spun antenna beam that fully covers the 
Earth. 
An input filter. 
A redundant UHF receiver which provides low-noise amplification for the SAR channel. 
A non-redundant SAR transponder which provides channel filtering, amplification, and up-
conversion for the SAR channel.  The SAR channel has fixed gain and bandwidth. 
A wave-guide output multiplexer (OMUX) in which the SAR signals are multiplexed with 
the other L-band downlink signals. 
An L-band transmit antenna comprising an array of dipoles arranged in 32 columns each 
with 4 dipoles connected in parallel.  The columns of this array are also electronically 
switched to make a de-spun antenna beam that fully covers the Earth. 
Figure 6-1: MSG Search and Rescue Repeater Functional Diagram 


6-2

6.2 
MSG Repeater Operating Modes 
The only operating modes of the MSG SAR payload are SAR transponder off and on. The mode 
switching operations must be performed by EUMETSAT. 
6.3 
MSG Repeater Spectrum Characteristics 
The spectral occupancy of the transmitted signal is shown in Figure 6.2. 
Figure 6-2: MSG L-Band Transmitter Output Spectral Occupancy 
The received beacon signals in the nominal 60 kHz uplink band from 406.020 MHz to 
406.080 MHz, are directly translated to the L-band downlink centred at 1,544.5 MHz.  The signal 
is not converted to baseband or a low intermediate frequency at any point.  Signals at 406.05 MHz 
are converted to 1,544.5 MHz. The frequency stability is ±6 ppm and ±9 ppm at beginning and 


 
6-3 
 
 

end of satellite life respectively.  The main filtering of the band is performed in the SAR 
transponder block using a SAW filter operating in the uplink frequency band. 
 
The specified useful channel bandwidth is > 60 kHz.  The measurements (see Figure 6.3) indicate 
that a 0.5 dB-channel bandwidth of approximately 100 kHz is achieved. The measured 
noise-equivalent bandwidth is in the order of 180 kHz.  
 
 
Figure 6-3: Measured Pass-Band of MSG Transponder 
 
Although a single figure cannot be used to describe short term frequency conversion stability 
characteristics of the MSG GEOSAR payload, the phase noise table (Table 6.1) and phase noise 
spectrum (Figure 6.4) of the transmitter local oscillator (LO) as measured for the first MSG flight 
model provide an indication of anticipated MSG performance. 
 
 
 


 
6-4 
 
 

Table 6.1: MSG Transmitter LO Phase Noise 
 
Random Spurious Modulation 
Frequency 
Measured FM-1 [dBc/Hz] 
fo + 10Hz 

fo + 100Hz 

fo + 1KHz 

fo + 10KHz 

fo + 100KHz 

Figure 6-4: MSG Transmitter LO Phase Noise Spectrum Plot 
 
 
 


 
6-5 
 
 

6.3 
MSG Repeater Coverage Area 
 
Both the UHF receive antenna and the L-band transmit antenna provide coverage of the full 
Earth as seen from longitude 0.0°.  Both antenna boresights are slightly tilted to the North. 
The design of the SAR transponder has been based upon the following minimum satellite 
elevation angles: 
• from the emergency beacons: 5 degrees, 
• from the receive ground stations (GEOLUTs): 18 degrees. 
 
The geographical coverage area is indicated in Figure 6.5. 
  
 
 
Figure 6-5: MSG 5 o Elevation Angle Coverage Contour 
 
6.4 
MSG Repeater Performance Parameters 
 
The principal worst case MSG repeater performance parameters as measured on the first flight 
model are shown in Table 6.2. 
 
 
 
 


 
6-6 
 
 

Table 6.2: MSG SAR Repeater Performance Parameters 
 
Parameter 
Unit 
Values 
Uplink Centre Frequency 
MHz 
406.050 
Nominal Input Level at Antenna* 
dBW 
-176.9 
System Noise Temperature 
K 

Receive Antenna G/T 
dB/K 
-21.3 
Bandpass Characteristic 
Specified Band 
Measured 0.5 dB-Band 
Noise-Equivalent Band (approx.) 
 
kHz 
 
>60.0 
100.0 
180.0 
Dynamic Range† 
dB 
n/a 
Phase Linearity (overall in band, specified) 
deg 
4.0 
AM/PM Conversion 
°/dB 
0.9 
Image Rejection 
dB 
>80.0 
AGC Time Constant‡ 
 
No AGC 
Transponder Gain 
dB 
148§ 
Transponder Linearity (C/I) 
dB 
20.0 
Gain Stability (over Temperature, Frequency & Lifetime) 
dB pk-pk 
2.0 
Output Frequency Stability 
ppm 
± 9 
Downlink Centre Frequency 
MHz 
1,544.5 
Downlink Polarisation 
 
Lin. Horiz. 
Maximum Output Power of Transmitter 
dBW 
0.0 
Repeater EIRP per Useful Carrier** 
dBW 
-19.0 
Modulation Type 
 
As uplink 
Transmitter Nominal Modulation Index 
 
As uplink 
6.5 
MSG SAR Antennas 
The MSG satellite spins at a rate of 100 rpm ± 1%.  To provide continuous coverage of a portion 
of the earth’s surface, the MSG SAR instrument utilises electronically switched de-spun antennas.  
The electronic switching has a cyclical impact on the performance of the transmit and receive 
antennas as described below. 
 
 
 
 
 
* Nominal input level at antenna from a 5 Watt Cospas-Sarsat beacon located at 5° elevation angle to the satellite. 
Includes 6.8 dB polarisation loss. 
† This is a transparent transponder. It is driven by noise so that dynamic range is less relevant. 
‡ The SAR transponder operates only in fixed-gain mode. 
§ Signal gain is sensitive to the composite power loading of the transponder (which is dominated by noise).  Strong 
ground interference may cause a reduction of gain.  Link margin can be provided by adequate receiving ground 
station G/T selection. 
** Assumes two beacons operating at nominal levels and 3 interfering carriers transmitted from ground with EIRP 3 dB 
higher than the beacon signals and randomly distributed within 60 kHz operational bandwidth. 


 
6-7 
 
 

6.5.1 
MSG SAR Receive Antenna 
 
The MSG SAR instrument uses an electronically switched de-spun (ESDA) right hand 
circularly polarised receive antenna, with gain performance as depicted at Figure 6.6.  The 
values provided in this figure represent the minimum dynamic gain over the coverage area, 
and with the satellite spin, the gain fluctuates above this value at a rate of 26.7 Hz.  The 
measured fluctuation (gain ripple) is 1.3 dB peak to peak in the south and up to 1.8 dB peak 
to peak in the north. 
 
The minimum gain (co-polar component) in the coverage area ranges from 3.1 dBi to 4.5 dBi, 
while during the scan the gain can be as high as 5.6 dBi.  The cross-polar component (XPD) 
varies in the coverage and ranges from -9.0 dB to 14.2 dB. 
 
Both the gain and the polarisation loss are directly involved in the uplink quality, the worst 
case combination of the two effects has been estimated: min[(Gain   Polarisation Loss)].  This 
occurs at a point in the west of the coverage where G = 3.45 dBi and XPD = 9 dB 
(i.e., polarisation loss = -6.78 dB).  Since this represents the worst case situation, these values 
should be used when designing GEOLUTs which will operate with the MSG satellite. 
 
6.5.2 
MSG SAR Transmit Antenna 
 
The MSG SAR instrument uses an electronically switched de-spun (ESDA) horizontally 
polarised transmit antenna, with typical gain performance as depicted at Figure 6.7. The 
values provided in this figure represent the minimum dynamic gain over the coverage area, 
and with the satellite spin, the gain fluctuates above this value at a rate of 53.3 Hz.  The 
measured fluctuation (gain ripple) is typically 0.8 dB and will not exceed 1.6 dB peak to peak 
from column to column. 
 


 
6-8 
 
 

Figure 6-6: MSG SAR Receive Antenna Pattern 


 
6-9 
 
 

Figure 6-7: MSG SAR Transmit Antenna Pattern 
 
Note: The figures depicted above depict the antenna gain at 1,544.5 MHz. 
 
 
 
- END OF SECTION 6 -


 
7-1 
 
 

7. 
LOUCH-5A GEOSAR REPEATER 
7.1 
Louch-5A Repeater Functional Description 
A functional block diagram of the combined SAR and environmental data dissemination network 
(EDDN) channels transponder is shown in Figure 7.1. The transponder comprises the following: 
 
a. 
Low noise amplifier that enables minimal effective noise temperature of the transponder 
 
b. 
SAR channel filter with 80 kHz pass band (at -3 dB)  
 
c. 
Down-converter that translates the input signal down to a first IF band (41.375±0.5 MHz) 
 
d. 
Amplifier (gain not less than minus 10 dB) 
 
 
 
Figure 7-1: Louch-5A Combined SAR and EDDN Transponder 
 
7.2 
Louch-5A Repeater Operating Modes 
The only operating modes of the Louch-5A SAR payload are SAR transponder on and off with 
gain setting variation. 
7.3 
Louch-5A Spectrum Characteristics 
The spectral occupancy of the transmitted signal is shown in Figure 7.2. 
 
 
LNA
Filter
Down. 
Conv. 1
Down. 
Conv.2
OSC
Amp
EDDN
SAR
EDDN
EDDN
SAR
SAR
From receive 
antenna
To transmit 
antenna


7-2

Figure 7-2: Louch-5A Transmitter Spectrum Occupancy 
7.4 
Louch-5A Coverage Area 
The 0-, 5- and 10-degree elevation angle coverage contours for the Louch-5A is shown in 
Figure 7.3. The zones are determined with the following orbit parameters: 
•
Sidereal period = 86164 ± 1 sec
•
Eccentricity = 0.0 - 0.0006
•
Inclination = 0˚ - 5˚
7.5 
Louch-5A Repeater Performance Characteristics 
The principal Louch-5A repeater performance parameters are shown in Tables 7.1. and 7.2 for 
SAR receiver and SAR transmitter respectively. 
Louch-5A combined SAR and EDDN channels transponder has fixed gain factor over the range 
between LNA input and power amplifier output. The value of the gain factor can be command set 
and by default is 138 dB. 


 
7-3 
 
 

Figure 7-3: Louch-5A Coverage Zones for 0, 5 and 10 Degrees of Elevation Angle 
 
 
Table 7.1: Louch-5A SAR Receiver Parameters 
 
No. 
Parameter 
Unit 
Values 
1. 
Operational bandwidth 
Mhz 
406.01-406.09 
2. 
Signal nominal level at LNA input 
dBW 

3. 
G/Т (at the edge of service zone) 
dB/K 
-10.2 
4. 
Receiver Bandpass Characteristics: 
kHz 
±40 (at -3dB) 
5. 
Dynamic Range (for SAR channel relative to 
nominal level -159 dBW) 
dB 
±10 
6. 
Image Rejection 
dB 
not less than 50 
7. 
Frequency Stability for: 
24 hours: 
100000 hours 
 
 
±1*10-8  
±1*10-7 
 
 
 


 
7-4 
 
 

Table 7.2: Louch-5A SAR Transmitter Parameters 
 
No. 
Parameter 
Unit 
Values 
1. 
Transmitter frequency range 
MHz 
1544.458-1544.542 
2. 
Output Power of Transmitter* 
dBW 
-10.2 
3. 
Repeater EIRP 
dBW 
7.1 
4. 
Phase Jitter (in 50 Hz bandwidth) 
deg 
0.6 
5. 
Modulation Type 
Radian 
 n/a 
6. 
Frequency Stability for: 
24 hours: 
100000 hours: 
МHz 
 
±1*10-8  
±2*10-7 
7. 
Amplitude Ripple  
dB 
less than 1.0 
8. 
Linearity 
dB 

7.6 
Louch-5A SAR Antennas 
 
The reception of the SAR signal is provided by four spiral P-band phased array antenna. The transmit 
antenna is a four spiral L-band phased array antenna. Both antennas have global beam (17˚x17˚ 
beamwidth). 
 
The receive antenna is a right hand circular polarized (RHCP) with an on-axis gain of 18.3 dB (16.2 on 
the edge of the coverage) and axial ratio of 0.7. The receive line loss between the antenna terminal 
and the low noise preamplifier is 0.6 dB. 
 
The transmit antenna is a right hand circular polarized (RHCP) with an on-axis gain of 19.9 dB 
(17.1 on the edge of the coverage) and axial ratio of 0.9. The transmit line loss between the antenna 
terminal and the low noise preamplifier is 1 dB. 
 
The receive and transmit antenna patterns are shown in Figures 7.4 and 7.5 respectively. 
 
 
 
 
 
 
 
 
 
 
 
 
 
* Since the power amplifier installed in the transponder is shared between SAR and EDDN channels the maximum 
SAR channel output power is not greater than 100 mW (in linear mode) 


 
7-5 
 
 

Figure 7-4: Louch-5A Receive Antenna Pattern at 406.05 MHz 
 
 
 
Figure 7-5: Louch-5A Transmit Antenna Pattern at 1544.5 MHz 
 
 
 
- END OF SECTION 7 - 
 


 
8-1 
 
 

8. 
MTG 406 MHZ GEOSAR REPEATER 
8.1 
MTG Repeater Functional Description 
The MTG SAR repeater main elements are shown in the functional block diagram. 
 
a) 
A UHF-band receive antenna based on direct radiating array architecture. 
b) 
An input cover filter. 
c) 
A redundant UHF front end which provides low noise amplification. 
d) 
A non-redundant section including OCXO, frequency down/up conversion, channel 
filtering and amplification up to 5 W. 
e) 
An output cavity filter. 
f) 
An L-band transmit antenna based on direct radiating array architecture. 
 
 
Figure 8-1: MTG SAR Repeater Functional Block Diagram 
8.2 
MTG Repeater Operating Modes 
The MTG SAR repeater can operate in two selectable bandwidth modes, narrowband (50 kHz) 
and wideband (90 kHz). It has a fixed gain control with 30 dB range, adjustable by telecommand, 
with nominal steps of 1 dB. 
 
There are two selectable translation frequencies which are the same for narrowband and wideband 
modes, resulting in the following downlink center frequencies: 
• 1544.3 MHz and 1544.5 MHz for the wideband mode, 
• 1544.293 MHz and 1544.493 MHz for the narrowband mode. 


 
8-2 
 
 

8.3 
MTG Repeater Spectrum Characteristics 
The MTG SAR transmit spectrum is shaped by the selectable IF crystal filters which define the 
pass band. Figures 8.2 and 8.3 show a typical spectrum at L-band output for narrowband and 
wideband modes. 
 
 
Figure 8-2: MTG Repeater Output Spectrum (Narrowband Mode) 
 
 
 
Figure 8-3: MTG Repeater Output Spectrum (Wideband Mode) 
 
 


 
8-3 
 
 

The bandpass characteristics of the MTG SAR repeater are shown in Figures 8-4 and 8-5 for 
narrowband and wideband modes. 
 
 
Figure 8-4: MTG SAR Repeater Narrowband Filter Performance 
 
 
 
Figure 8-5: MTG SAR Repeater Wideband Filter Performance 
 


 
8-4 
 
 

8.4 
MTG Repeater Coverage Area 
The MTG SAR repeater is designed to cover the full visible Earth’s disc (elevation > 5°) both in 
the UHF uplink and in the L-band downlink. The antenna patterns, including peak gain, are 
included in section 8.5. 
8.5 
MTG Repeater Performance Parameters 
Table 8.1: MTG SAR Repeater Performance Parameters 
 
Parameter 
Values 
Unit 
Receive centre frequency –wideband mode 
406.050 
MHz 
Receive centre frequency –narrowband mode 
406.043 
MHz 
Minimum input level at antenna  

dBW 
Receive antenna polarization 
RHCP 
 
Receive antenna axial ratio 
< 3.2 
dB 
Receive antenna gain at end of coverage 

dBi 
Satellite G/T at edge of coverage 
-15.5 
dB/K 
Transponder gain (w/o antennas) 
134 - 163 
dB 
Transmit antenna gain at end of coverage 
11.9 
dBi 
Transponder linearity 
> 30  
dBc 
Short term frequency stability (100ms) 
< 1.0 x -10 
 
Group delay over 4 kHz 
< 10 
us/4kHz 
Downlink frequency stability 
Short term worst case 
Long term worst case 
 
± 0.27 
± 1.5 
 
ppm 
ppm 
Translation frequencies (selectable) 
1138.45  
1138.25 
MHz 
MHz 
Downlink center frequencies 
Wideband mode 
Narrowband mode 
 
1544.5 or 1544.3 
1544.493 or 1544.293 
 
MHz 
MHz 
Downlink max EIRP 
Downlink nom EIRP* 
> 15 
2.5 
dBW 
dBW 
Transmit antenna axial ratio 
< 2.5 
dB 
Transmit antenna polarization 
RHCP 
 
 
* The nominal EIRP is computed with FGM step 9 and the assumed loading scenario is two beacons 
operating at nominal levels (EIRP=37 dBm) and three additional beacons at EIRP 3 dB higher. 
8.6 
MTG SAR Antennas 
The receive and transmit antennas make use of Direct Radiating Array (DRA) architecture. 
Figures 8-6 and 8-7 show examples of the UHF and L-band co-polar gain patterns. 


 
8-5 
 
 

Figure 8-6: MTG UHF-Band Antenna Co-Polar Amplitude Pattern 
(Antenna Gain in dB Relative to the Peak Gain of 14.2 dBi; Red Circle Shows the Earth)  
 
 
Figure 8-7: MTG L-Band Antenna Co-Polar Amplitude Pattern 
(Antenna Gain in dB Relative to the Peak Gain of 14.2 dBi; Red Circle Shows the Earth) 
 
 
- END OF SECTION 8 – 
 
 
- END OF DOCUMENT -


 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
 
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