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Full-duplex voice and data transceiver

The Radiodata SEM F-221 sometimes identified as the RDN-221 1 , was a full-duplex radio for voice and data traffic, introduced in 1987 by RDN Radiodata GmbH in Dehlewitz (Germany), for use by the German public safety services (BOS). 2 The radio operates in the 2 m radio band and is in fact a modified version of the SE-221 radio of 1981 made by Standard Electric Lorenz (SEL) [1].

The radio set was developed especially for use in combination with the Telefunken Telestar 121 mobile data terminal, just like the Bosch KF-802 (FuG-8b/c) that was used by some German BOS services, such as the police and the fire brigade.

A complete system consisted of the Radiodata SEM F-221-1620 GW51/D transceiver – i.e. the modified SEL radio – and the BG-217-5/FRP remote control unit [1]. The latter was basically a standard BG 217-4/5 unit, of which the existing hardware and software had been modified by RDN, to provide control over the extra features.
Complete set

The sets were modified for full duplex data traffic on BOS channels 101 — 125. Although mainly used for sending text messages via the Telestar terminal, it was also possible to place voice calls. This feature was hardly used however, as there were no handheld radios for these channels at the time. Many RDN-221 sets were delivered to the Ministry of Internal Affairs of the German County of Rheinland Pfalz during the course of 1987 and 1988. They were used until at least 2004 [1].

  1. Although this name is officially incorrect, we are using it here as an abbreviated form of the full name, which is simply too long and too complicated: SEM F-221-1620 GW51/D with BG-217-5/FRP.
  2. BOS = Behörden und Organisationen mit Sicherheitsaufgaben (Public Safety Organisations).  More

Complete set Transceiver, front side SEM F 221-1620 GE51/D transceiver GB 217-5/FRP control unit Control unit, rear side Front panel Complete set with cables Close-up of some connectors
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Complete set
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Transceiver, front side
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SEM F 221-1620 GE51/D transceiver
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GB 217-5/FRP control unit
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Control unit, rear side
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Front panel
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Complete set with cables
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Close-up of some connectors

All user interaction is via the clear control panel on the modified BG-247 remote control unit, as shown in the diagram below. It consists of 20 push-buttons, a clear liquid crystal display (LCD) and 4 indicator lights. The global operation is controlled with the buttons at the lower edge. The radio is turned ON and OFF with the leftmost push-button (E/A). A channel can be selected by pressing the (C) button followed by a 3-digit channel number (101-125). Use (✱) for corrections.

Four indicator lights along the upper edge show the current state of the radio. The first yellow LED is lit when the speaker is switched ON. The second yellow LED blinks when a call is waiting to be answered. The remaining LEDs are lit when the radio is receiving (red) or transmitting (green). The radio can send several tones for selective and non-selective calls, activated by pressing the (R) button followed by one of the number buttons (0-9). The following tones are implemented:

  • R1
    1750 Hz continuous tone for repeater operation
  • R2
    2135 Hz continuous tone for repeater operation
  • R3
    Scan-Stop tone (initiates conversation with control center)
  • R4
    2800 Hz continuous tone (call all)
  • R5
    5-tone sequency (starts scanning at the control center)
If necessary, it is possible to select a different frequency band or a different mode of operation, by using the (U/O) and (G/W) buttons. The current selection is reflected in the horizontal dashes in the rightmost position of the display. (U/O) and (G/W) have the following meaning:

  • U
    Lower band (German: Unterband)
  • O
    Upper band (German: Oberband)
  • G
    Duplex (German: Gegensprechen)
  • W
    Simplex (German: Wechselsprechen)
The diagram below shows the layout of the display (LCD). At the far left is the subscriber number of the other party, for outgoing calls. The number is entered via the numerical keypad, after which the call is initiated by pressing the (Z) button. The second groups shows the subscriber number of an incoming call. The letter 'P' is shows when CTCSS is enabled (P = pilot tone).

The number group at the right represents the selected radio channel. It is prefixed by the letter 'C', whilst the first '1' of the channel number is omitted. In the example (C05) channel 105 is selected. Two horizontal dashes at the far right of the display, indicate the setting of the U/O (band) and G/W (mode) selectors. There settings are usually pre-defined for the selected channel.

The device is based on the SE-221 (also known as the SEL-221), a full-duplex radio for the 2-meter band, developed in 1981 by Standard Electric Lorenz (SEL) and in production from 1983 onwards. The SEL-221 is based on the earlier FuG-9b 1 /FuG-9c 2 devices that operated on BOS channels 01—92. SEL eventually solds its product line to Bosch, where the devices were produced for many years, until Bosch sold its mobile radio portfolio to Motorola in 1997.

Radiodata was a relatively small company which had a good and close relationship with Bosch. In many cases they developed products for markets that were too small for Bosch, some of which were even sold under the Bosch brandname. When the German Government of the Country of Rheinland Pfalz needed a new emergency system for their public safety services, or BOS, (German: Katastrophenschutz, or KatS), Radiodata was commissioned to develop the necessary equipment.

The SEL-221 (by now produced by Bosch) was used as the starting point. It was heavily modified by Radiodata, who converted it for use on the BOS channels 101—125, and added its own RDN data modem. The existing control unit (German: Bediengerät, or BG) was modified for the extra features. Furthermore, an interface was provided for the Telefunken Telestar 121 data terminals.

The devices were delivered to the Ministry of Internal Affairs of the County of Rheinland Pfalz, during the course of 1987 and 1988, after which they were in service until approx. 2004. The devices can be recognised by the blue RDN-logo on the front panel.

  1. The suffix 'b' indicates a standard device.
  2. The suffix 'c' indicates a device with a special control unit, with relay contact.

Full-duplex transceiver SEM F 221-1620 GW51/D Remote control unit BG 217-5/FRP Telefunken Telestar 121 data terminal Cables for connection of the various units
Transceiver   SEM F 221-1620 GW51/D
The transceiver is based on the SE-221 that was developed by Standard Electric Lorenz (SEL) in 1981 and produced from approx. 1983 onwards. Radiodata added its own RDN radio data modem and made the radio suitable for full-duplex data.

The transceiver has a standard form factor, so that it fits existing installations and mounting brackets. It does not have any direct controls. Instead it is controlled by the external BG-217 Bediengerät (control unit) that is connected via the 37-pin sub-D connector (DB37) at the front.

SEM F 221-1620 GE51/D transceiver

Control unit   BG 217-5/FRP
All functions of the transceiver are controlled by the external control unit shown in the image on the right. It is basically a BG 217-4/5 of which the hardware and software have been modified, resulting in the BG 217-5/FRP that has the same form factor and fits in the existing space.

The hardware is modified for CTCSS use, and a 10-pin socket is provided for connection of the standard handset. The software was modified for CTCSS and selective tone call (SELCALL), using a unique 5-tone sequence to address each radio.

GB 217-5/FRP control unit

Data terminal   Telestar
Especially for the so-called Katastrophenschutz (KatS) – the regional emergency management system – the radios were equipped with Telestar 121 data terminals made by Telefunken. The image on the right shows a typical Telestar 121.

These terminals were also used by the German Federal Police, German Customs (Zoll) and the Bundesgrenzschutz (BGS), for connection to the nationwide INPOL information system. Telestar terminals were also used by NATO.

 More information

Telefunken Telestar 121

The radio came with a full set of cables for connecting the transceiver to the control unit, the control unit to the data terminal and – for plain voice conversations – to the handset.

The image on the right shows the audio cable that connects the handset – via the data terminal – to the control unit. By routing it via the data terminal, the latter can be used to select between data and voice traffic.
Audio cables

Complete set with cables Audio cables Audio cables Close-up of some connectors Remote control cable Data cable
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Complete set with cables
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Audio cables
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Audio cables
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Close-up of some connectors
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Remote control cable
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Data cable

BG   Bediengerät
Control unit.
CTCSS   Continuous Tone Coded Squelch System
Continuous sub-audible audio tone, that is send with a voice transmission in order to open the noise cancelling system (squelch) of the receiver at the other end. Commonly used with transmissions via a repeating station (repeater). Also known as Pilot Tone (P).
G   Gegensprechen
Operation via repeater. In this case it means duplex operation.
O   Oberband
Upper frequency band.
SE   Sender/Empfänger
Transceiver (transmitter/receiver).
U   Unterband
Lower frequency band.
W   Wechselsprechen
Simplex operation.
  1. Systembeschreibung Feuerwehr Funksystem Rheinland-Pfalz
    BG 217-5/FRP. Radiodata Nachrichten-Technik, October 1987. 1
  1. Document kindly provided by Klaus Paffenholz [1].

  1. Klaus Paffenholz, Radiodata SEM F 221-1620 GW51/D mit BG 217-5/FRP
    Retrieved January 2018.
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Crypto Museum. Created: Friday 12 January 2018. Last changed: Monday, 15 January 2018 - 09:47 CET.
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