SEM 25
The SEM 25 (transmitter / receiver, mobile) is now a rarely used VHF two- way radio, primarily for vehicle installation (24 volts). It was developed and manufactured by the company SEL for vehicles of the Bundeswehr . It had been in use since the 1960s and was replaced by the SEM 80/90 in 1986 .
The device works in the frequency range from 26.00 to 69.95 MHz with a grid of 50 kHz and thus has 880 channels. Ten frequencies can be preset. The transmitter can be switched to two power levels: 1 W and 15 W. The type of modulation used is FM G3 . There is also a pure receiver version as EM 25 , both of which can be connected together or two of each device to form a relay. The device consists of three assemblies: the base plate, the actual transceiver and an SE control unit that can be removed up to 10 meters. The transmitter output stage is equipped with tubes, otherwise the SEM 25 is fully transistorized. The combination of two SEM 25 allows relay operation. The prerequisite for this is that the base plates of both devices are connected to connections 52 and 51 and that operation is set to "Relay". For the radio typist VHF (in a UNIMOG box body and also in an M113 MTW as armored radio typist VHF) the SEM 25 with the WT-FM-E1 AP01 MODEM (modulator / demodulator with audio frequencies in the voice band) and the teletypewriter SIEMENS T100 expanded and could therefore also be used for wireless telex. The AGAT antenna adapter was available as an accessory (also on an extendable mast as ASB = antenna stand operation), which adjusted the antenna automatically depending on the frequency, the antenna connections were standardized according to BNC, a control line for the AGAT is a prerequisite for the tuning process.
The comparable SEM 35 was introduced for portable use .
For operational use, there is also the option of operating the SEM 25 via a two-wire line with a telephony device if the in-house communication device is connected to the device. This makes it possible, for example, to radio the operation in a field HQ, even if the vehicle with the SEM 25 is far away (depending on the length of the field line) or from a hidden position or a bunker.
For the training there is the radio interference simulator ECM / FSS 209 , which can be switched between the handset and the microphone input of the SEM 25 or a training system.
As with the SEM 35, the H-33F / PT from the H-33 series is usually used as the handset . The LF connection is a U-127-U-specified NATO plug and is assigned as follows:
- A = receiving tone (Rx +)
- B = receiving tone (Rx -)
- C = microphone (Tx +)
- D = switched 6 V power supply for carbon microphone
- E = 6 V voltage output for carbon microphone
- F = PTT (TX = on ground)
- H = mass
- J = switch off at 24 V.
- K = unused
- L = receiving tone, unregulated (regardless of volume setting)
B and H can also be connected together.
The lid of the microphone capsule can be twisted off so that a replacement capsule of type M-35 / U can be used. This was manufactured by the company Audiosears with the model number 1277 and is compatible with the H-33 E and the H-33 F / PT.