Direction Finders
Locator Beacons
Emergency Receivers
SAR Direction Finder System for Rescue Missions at Sea


Mobile Land
The RT-500-M is a multi-band direction finder system that operates on all frequency bands used for rescue missions. This direction finder automatically monitors the emergency frequencies 121.500 MHz, 243.000 MHz and 406.028 MHz (Cospas-Sarsat) as well as channel 16 of the marine band. The bright TFT display permits a clear overview of all direction finder information and operating parameters. A convenient menu structure makes it possible to adapt the RT-500-M direction finder system to the needs of the user. Various interfaces (LAN, NMEA RS-422, RS-232) facilitate integration of the direction finder system in legacy or planned system environments.


The RT-500-M direction finder system fully meets the steadily increasing needs of modern civilian and military search-and-rescue organizations. Emergency beacons that operate on the 406.028 MHz Cospas-Sarsat frequency can be reliably identified and localized. Like all RHOTHETA direction finder systems, the RT-500-M features complete MOB functionality to ensure the safety of SAR crew members. That makes the RT-500-M direction finder system a complete solution for professional SAR organizations.

Although the RT-500-M was optimized for use in high sea states, this direction finder system is also suitable for stationary VTS applications.

Special Features

  • Universal multi-band direction finder: VHF aviation and marine band, UHF aviation band, Cospas-Sarsat frequency
  • Automatic monitoring of emergency frequencies during work on other frequency bands
  • High reception sensitivity to permit detection of extremely weak or distant signals
  • High direction finder accuracy, precise and stable display
  • LAN, NMEA, RS-422 and RS-232 interfaces for system integration and remote control
  • Optimized for use at sea: robust construction, waterproof (IP67) display/control unit and antenna
  • Compact broadband antenna system (Patent DE 4421759 C1)
  • Graphic TFT color display, especially bright (450 cd/m 2)
  • Remote control unit for exterior control platform with full control and display functionality
  • Complete illumination with automatic dimming as a function of ambient light conditions


Electronical Characteristics

Method of bearing Doppler-principle (3 kHz rotational frequency, right / left rotation)
Bearing Indication Relative bearing and True bearing (if ext. heading data available)
Bearing accuracy ±5°
Internal resolution
Sensitivity RF-voltage at receiver-input (50 Ohm): VHF < 100 nV; Marineband < 100 nV; UHF < 100 nV; 406 MHz < 150 nV
Frequency stability ±2.0 ppm (Δf/f=±2·10-6) [in temperatur range -30°C ... +80°C]
Receiving bands 4 (VHF-Airband; VHF-Marineband, UHF-Airband; Cospas/Sarsat)
Receiving requency VHF air band: 118.000 ... 121.500 ... 122.975 MHz
VHF marine band: 156.000 ... 156.800 ... 162.025 MHz (Channel 0 ... 28, 60 ... 88, Sea+Coast)
UHF air band: 240.000 ... 243.000 ... 245.975 MHz
Cospas/Sarsat: 400.000 ... 406.025 ... 409.975 MHz
Channel pattern 25 kHz
Scanning / Monitoring mode Monitoring:
While normal operating, 4 additional frequencies will be surveilled. (Emergency frequencies 121.500; 243.000 and two free selectable frequencies)
In Standby mode the emergency frequencies, the Cospas/Sarsat and one free selectable frequency is always surveilled.
Signal Filtering Optional, all emergency frequencies can be filtered for ELT-modulation. (Disabling false alarms)
Cospas/Sarsat analysis Reception and analysis of Cospas/Sarsat data signal (112 resp. 144 bit, 400 baud, biphase L-phase modulated, with Bose-Chaudhuri-Hocquenghem error test/ specified according Cospas/Sarsat)C/S T.001 October 1999)
Indication of datacontent (mode, country, GPS-coordinates)
Bearable kinds of modulation A3E, F3E, A3X (ELT-modulation)
bearing largely independent of modulation
Polarisation Vertical
Error of polarisation ≤ 5° at 60° field vector rotation
Garbling cone app. 30° to the vertical
Time of response ≤ 50 ms (with sufficient receiving field strength)
Keyboard Foil on the front with integrated keyboard-matrix and EL-background illumination
TFT graphic display 320 x 240 pixel with max brightness of app. 450 cd/m², continuously variable brightness
Operating voltage 12 V ... 30 V DC
Current consumption app. 2.5 A max.
Audio External Speaker 4W (4 Ohm, 8 Ohm )
Line Out (adjustable from 100 mV pp to 2000 mV pp)
Interfaces NMEA Input/Output (RS422 and RS232)
Ethernet LAN
Testport (RS232) optional custom-specific
Alarm relay output (1 A, 30 V DC / 0.3 A, 125 V AC)
PTT input for self bearing suspression
Squelch output for external audio controlling

Mechanical Characteristics

Display Control Unit (DCU)

Weight app. 1200 g (2.7 lbs)
Tolerable operating temperature -20°C ... +60°C
Protection system IP 67

Antenna Unit (AU)

Weight app. 5200 g (11.7 lbs)
Tolerable operating temperature -40°C ... +60°C
Protection system IP 67



Rt_500_m_right Rt_500_m_antenna