SEM 25

Some description from the nice web-site   http://www.nf6x.net/1999/06/the-german-sem-25-transceiver/

The SEM-25 is a West German short-range tactical vehicular VHF FM transceiver which was introduced in the 1960’s, and was apparently used until at least the 1980’s.

The SEM-25 covers 26.00 to 69.95 MHz, in 50 kHz steps. It is all solid-state, except for three tubes in the transmitter power amplifier. A SEM-25 system will typically consist of at least the following items:

  • Transceiver chassis
  • Control box (may be mounted on front of transceiver, or remotely)
  • Mounting/power supply
  • Power transient suppressor
  • Antenna tuning unit
  • Antenna
  • Audio accessories ranging from a simple handset to several junction boxes and headsets
  • Various cables

More complicated systems may consist of two SEM-25 transceivers and one EM-25 receiver, with lots of audio gear and cabling, thus providing a set with retransmission and intercom features.

The “SEM” in “SEM-25” is short for “Sender-Empfangsgerät”, which is German for “transmitter-receiver”. Similarly, the “EM” in “EM-25” is short for “Empfangsgerät”, which is German for “receiver”.

Specifications

General

 

Modes Simplex, retransmit
Frequency range 26.00-69.95 MHz
Channel spacing 50 kHz
Number of channels 880
Channel selection 44 1-MHz bands, 20 50-kHz channels each
Programmable channels 10
Modulation FM
Operation, including frequency selection Operated from a transceiver-mounted control box, or from a relocatable control box in vehicle (max. cable length 10m)
Transmitter operation
  1. From handset or aux. receiver
  2. From on-board intercom
  3. From telephone remote control
Remote input and output arrangement From telephone remote control over field phone wires, up to 3 km long, max. resistance 480 ohms
Temperature range Operating range from -45°C to +60°C
Overvoltage protector For transients up to 65V from the battery regulator
Power supply 24V battery supply, negative ground, permissible voltage range 21V to 29V, short term overvoltage up to 32V

 

Transmitter

 

Output power High: 15 W
Low: approx. 1 W
Calling frequency 1600 Hz
Audio input
  1. 0.25 V from 150 ohm carbon microphone
  2. 0 dB from 600 ohm balanced line
Warm-up time approx. 30 seconds

 

Receiver

 

Sensitivity <= 0.5 µV for 20 dB s/n with 1000 Hz modulation and 10.5 kHz deviation
Bandwidth >= 30 kHz at 6 dB points
Selectivity +/- 50 kHz at 80 dB points
Audio output
  1. 0.6 W into 5 ohm loudspeaker
  2. 50 mW into 600 ohm headset
  3. 1 mW into 600 ohm balanced line

 

Power Supply

 

Voltage 24V battery (21V to 29V), negative ground, permissible short term overvoltage up to 32V
Power requirements, RX approx. 10 W
Power requirements, TX Low approx. 50 W while transmitting
Power requirements, TX High approx. 80 W while transmitting
Power requirements, TX Low or TX High approx. 29 W when not transmitting

 

Sizes and Weights

 

Item Height (mm) Width (mm) Depth (mm) Weight (kg)
Control box 174 228 75.5 2.54
Transceiver 222 268 255 14.59
Transceiver mount 120 320 300 9.43
Receiver 222 196 255 11.08
Receiver mount 120 320 230 6.68
Antenna tuning unit 122 290 110 3.70
Overvoltage protector 93 250 126 2.62
Spares case 48 140 140 0.73

My SEM-25