Jun 071999
 

SEM-25 Transceiver, with Canvas Cover
This page describes the German SEM-25 transceiver. I compiled this information to help other collectors who have (or are thinking of getting) a SEM-25, but cannot find technical information about it; manuals and schematics for this set are very rare in the U.S. at this time.

Please note that I do not have any original manuals for this set, and I do not even have a complete set of copied manuals (for example, I do not have any aligment procedures, and I would have great difficulty understanding them even if I had them due to my very poor command of the German language). I cannot provide any further information beyond what is described here at this time, and I cannot provide manual photocopies or other printed information at this time. This page truly contains everything I know about the SEM-25!

Please comment me if you discover any errors in this paper.

I hope you find this information useful!

 


Description

 

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. Although surplus SEM-25 radios are not yet very common in the U.S., some have recently appeared on the U.S. surplus market from vendors such as Murphy’s Surplus Warehouse.

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.

So far, I have only obtained a transceiver chassis, control box and mounting, so I cannot provide much information about the antenna, antenna tuning unit, power surge protector or other accessories at this time. The audio connections on the control box and main chassis are compatible with common 1950’s U.S. audio accessories such as the H-33/PT handset and LS-166/U loudspeaker. Pictures I have seen of the correct German audio accessories (well, actually photocopied photocopied photocopies…) suggest that the correct German handset (called an H-33G) appears virtually identical to its U.S. counterpart, and the correct loudspeaker has a case like a U.S. LS-7 loudspeaker with a mounting like a U.S. LS-166. The headset looks a lot like a U.S. H-63/U with an AN/GSA-6 control box. The antenna whip elements are called MS118AK, MS117A and MS116A, and look very similar to U.S. elements with similar names, and the antenna base looks a lot like the U.S. MP-65. The knobs on the control box look just like 1950’s U.S. knobs. I’m really surprised at the similarities between this set and comparable U.S. sets, in spite of the fact that they were designed and built in different countries.

I first learned of the existence of the SEM-25 when I saw a pile of them on the shelves in the famous back room of Murphy’s shop in late 1998. Although I had never been very interested in foreign military gear before, the SEM-25 looked like a neat radio, so I talked my folks into getting me one for Christmas in 1998. My dad and I made the hour-long drive down to Murphy’s shop on Christmas Eve, and I picked out the nicest-looking radio from the pile. It was even gift-wrapped in a stylish olive drab canvas cover!

At the time, Mike was charging $350 for the SEM-25, and $250 for a smaller but similar-looking radio which he called a “SEM-20”. The smaller radio is actually an EM-25 receiver; it’s basically a receive-only version of the SEM-25. It’s easy to get confused about the features and identification of these two radios, because they both use the same control box and share many modules, so the EM-25 is prone to have stickers which say “SEM-25” (or even “SEM-35”; it shares two internal modules with the SEM-35 backpack transceiver) on and inside it, and it will have controls for transmitting functions which it does not perform.

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

 


Controls

This section decribes the functions of the controls on the SEM-25 control box.

 

Control Box

Ref. Description
A Channel programming drum (behind cover)
B Call button: Keys transmitter, sends 1600 Hz tone
C Squelch
D Volume
E Manual tuning, 1 MHz steps
F Manual tuning, 50 kHz steps
G Power
H Channel selector (H = manual tuning)
I Power-on light (turn bezel to dim)

 

 

 


Power Switch Settings (Ref. G)

 

AUS: Off
EMPF: Receive-only
SENDEN KLEIN: Transmit/receive (low power)
SENDEN GROSS: Transmit/receive (high power)

 


Squelch Switch Settings (Ref. C)

Note: Squelch is opened by carrier level, equivalent to “old” mode in U.S. radios.

 

RAUSCHSP. AUS: Squelch off
RAUSCHSP. EIN: Squelch on
RELAIS: Relay (retransmit)

 


Connectors

This section describes the functions of the external connectors on the SEM-25.

 

Connectors, Left Side Connectors, Front Connectors, Right Side

Ref. Description
J From transceiver #1 in multi-radio sets
K Antenna tuner control
L Antenna RF
M Power input
N Mounting/transceiver interconnect
O Audio
P Control box/mounting interconnect
Q Receiver fuse (2A)
R Transmitter fuse (6.3A)
S To transceiver #2 or aux. receiver in multi-radio sets

 

 

 


Modules

This section identifies the SEM-25’s major internal modules. Note that two of the modules (as noted below) are also used in the SEM-35 backpack/vehicular transceiver.

 

Main Chassis, Left Rear View Main Chassis, Right Rear View Main Chassis, Behind Front Panel Mounting/Power Supply

Ref. Description
N Mounting/transceiver interconnect (external)
O Audio connector (external)
P Control box/mounting interconnect (external)
Q Receiver fuse (2A) (external)
R Transmitter fuse (6.3A) (external)
T Transmitter RF
U Receiver RF
V Modulator amplifier, 1600 Hz tone generator, and 11.5 MHz discriminator for automatic frequency control (AFC) of transmitter
W Audio amplifier
X Receiver power supply and control amplifier
Y Frequency synthesizer (also used in SEM-35)
Z IF (Intermediate Frequency) module (also used in SEM-35)
AA Plugs for test box
BB 10-frequency crystal oscillator
CC Receiver servo
DD Transmitter servo
EE Transmitter power supply
FF Motor drive power supply for external antenna tuner
GG Relays for interconnect of multiple transceivers
HH 600 ohm balanced audio connections

 

 

 


Internal Adjustments

While we have the case open, here are some of the major internal adjustments:

 

Control Label Location Function
R36 Rauschperre Audio amp. (Ref. W) Squelch level
R5 NF-Pegel Audio amp. (Ref. W) Audio level
R13 Eing. Mod. amp. (Ref. V) Mod. amp. input gain
R26 Ausg. Mod. amp. (Ref. V) Mod. amp. output gain
R38 Tacho Rx power supply (Ref. X) Stepping speed trim (?)

 


Schematics

The diagrams in this section were scanned at 150 pixels per inch, and you will probably need to use an external graphics-editing program to print them (simply clicking your browser’s “Print” button probably won’t work well).

The diagrams were all scanned from photocopied manuals, and the originals are just as blurry as the scans, so don’t bother asking for photocopies of the schematics! :-)

 


Block Diagrams

Description File Size
Transceiver blk01.gif 1100×1338, 33k
Frequency selection blk02.gif 1100×1540, 44k
Receiver blk03.gif 1172×946, 20k
Transmitter blk04.gif 1082×888, 12k
Antenna tuner (external) blk05.gif 948×1240, 15k

 


Schematic Diagrams

The “Ref.” column shows the corresponding reference letters from the module identification pictures (where applicable), to help you figure out which part of the radio is described by each schematic.

Description Ref. File Size
Wiring (main chassis) sch01.gif 1744×1232, 90k
Transmitter RF T sch02.gif 1744×1232, 70k
Receiver RF U sch03.gif 1744×1232, 70k
Modulator amplifier module V sch04.gif 1744×1232, 62k
Audio amplifier module W sch05.gif 1744×1232, 55k
Receiver power supply module X sch06.gif 1744×1232, 66k
Frequency synthesizer module Y sch07.gif 2381×1231, 117k
IF module Z sch08.gif 2539×1232, 84k
10-freq. crystal oscillator BB sch09.gif 1193×768, 17k
Receiver servo CC sch10.gif 1196×778, 38k
Transmitter servo DD sch11.gif 1172×809, 19k
Control box sch12.gif 3042×1226, 104k
Wiring (mounting) sch13.gif 1744×1232, 94k
Transmitter power supply EE sch14.gif 778×1159, 36k
Motor drive power supply FF sch15.gif 1187×772, 26k
Interconnect relays GG sch16.gif 1197×794, 36k
Transient protector (external) sch17.gif 1201×790, 34k
Antenna tuner (external) sch18.gif 1744×1232, 68k

 


English/German Translations

This section lists rough translations of some German words, phrases and abbreviations as used in the SEM-25’s schematics, module labels, etc. My command of German is very poor, so there may be mistakes here… please comment if you can correct any of my translations!

Abstimmgerät
Radio tuner (tune + apparatus)
Abstimmteil
Radio tuner section (tune + part)
Additionsstufe
Addition stage
Anschluß
Connection
Antennen
Antennas
Antrieb
Drive, driver, motor
Ausgang
Output
Bausteinträger
Component carrier
Bauteile
Components
Bedien
Control head
Begrenzer
Limiter
Blockschaltbild
Block diagram
Bordbatterie
On-board battery
Bordverstärker
Intercom (on-board + amplifier)
Diskriminator
Discriminator
Eingang
Input
Einsatz
Part, component
Empf.
Receive or receiver
Empfänger
Receiver
Endstufe
Output stage
erdfrei
Balanced (i.e. “balanced line”; literally, “ground-free”)
Frequenzaufbereitung
Frequency synthesizer
Funk
Radio
geschlossen
Closed
gezeichnet
Drawn
gross
Large
Grundplatte
Mounting (base + plate)
HF
Radio frequency (RF)
Hinweis
Note
im
In
Kanalwahl
Channel selection
klein
Small
Leitung
Line, wire
Ltg.
Line, wire
Masse
Common, ground
Mischstufe
Mixer
Netzgerät
Mains power adapter
NF
Audio frequency
Oberton
Overtone
offen
Open
Oszillator
Oscillator
Prüfgerät
Test meter
quarz
Quartz
rauschperre
Squelch (noise + stop)
relais
Relay, retransmit
rufen
Call
ruhezustand
Off-state
senden
Transmit
Sender
Transmitter
Servoverstärker
Servo amplifier
Steuerverstärker
Servo amplifier
Stromversorgung
Power supply
Teil
Part
Transientschutz
Transient protector
Treibertufe
Driver stage
Trennstufe
Divider stage
Umwandler
Converter
Verstärker
Amplifier
Vorstufe
Input stage
ZF
Intermediate frequency (IF)

 


Credits

This work would not have been possible without the generous assistance of the following people:

Pictures were taken with a Sony MVC-FD91 digital camera. Reference letters were added with Visio 4 on a Windows NT box; all other image editing was performed with xv and gimp on a Redhat Linux system.

Scanned documents were scanned with a Umax Astra 1220S scanner and the SANE software under Redhat Linux, and then edited with xv and gimp.

 

  97 Responses to “The German SEM-25 Transceiver”

  1. Hello,
    I have a SEM-25 since several years…
    This morning, i decided to plug a 24v power supply and to see what happens…

    The receiving part is all ok

    But not in transmit. I try the “Call button” with the two modes (LOW and HIGH RF) but nothing.
    I just listen an internal relay.

    Perhaps no tube ? Hi

    I am searching the TX fuse but i did not found. On the panel it’s look like not similar than on your pictures.

    Some ideas ?

    I have a specific page where you can see my beautifull SEM-25. On this page i have re-writen the first pages of your nice web site and i hope that you agree with this.

    Thanks a lot
    Best 73
    JEAN-LUC
    F6HOY

    http://www.f6hoy.com/sem-25/

    • Hello Jean-Luc !
      I’ve taken a look on your SEM 25-Homepage and I found the reason why your SEM 25 will not transmit: I’m sure that the unit you own is NOT a SEM 25 but a EM 25. The Housing of the unit on top of the mounting (Receiver- or Transmitter/recceiver-unit) ist to small.
      On the frontside of the mounting there are 2 fuses – a 2A-fuse for the Receiver and a 6,3A-fuse for the transmitter. On your photos the 2A-Fuse is positioned on the right side, on the Frontside is NO Fuse. However, your unit is marked als “SEM 25” with a serial-number which is written by hand on the type shield, usually the serial number is printed . The only way to find out what’s wrong is: Open the mounting. Inside the TRX-Mounting are 3 Plug-in Units (Antrieb-Stromversorgung, Sender-Stromversorgung and Relaiseinsatz). If there are only 2 (Antrieb-Stromversorgung and Relaiseinsatz) the mounting belongs to the EM 25. 2.Step: Remove and open the “Main Group”on top of the mounting. Be very careful when opening the clamps !!! If there are 3 tubes on the right side, it’s a transmitter-receiver-unit, if there are no tubes, it’s a Receiver. You can compare the internal view of your units with the Pictures on Mark’s Homepage.
      I hope this informations are helpful for you.
      73,
      Klaus, DL4FCY

    • Hello Jean-Luc !
      On one of your photos i could see a part of the german stock-no. (Versorgungsnummer). It belongs to the mounting of the RECEIVER EM 25 (Stock-no/Versorgungsnummer 5820-12-141-1227).
      It is definitive Receiver…
      73,
      Klaus, DL4FCY

  2. Hi Jean-Luc !
    When switching on the Transceiver, you’ll have to wait a couple of minutes (2-3) before activating the Transmitter, until the tubes are “heated”. If you are changing the frequency, is the tuning circuit running ? If not, it could be a problem in the “Transmitter Power supply” (in German: Sender-Stromversorgung) which is located inside the mounting. On Marks Photography it is marked with “EE”.
    I hope this will help you to get your sem25 back on air !
    73,
    Klaus, DL4FCY

    • Hi Klaus,
      Thanks a lot.
      Yes, when i change frequency i can listen the circuit running.

      I think that i am going to open it.
      I will be at home tomorrow and i will look this…

      73
      Jean-Luc
      F6HOY

  3. Wonderful Web Page…..
    Sem35 Alignment help, Radio off just little between RECV TRX . Any Help Please.ThankX Mark

  4. Avatar

    Hi

    I have a simple question .
    What is the length of the ideal antenna with an AGAT ?

    Thank’s

    73
    Laurent

  5. Avatar

    Hello Laurent !
    The ideal length is the original Antenna : Antenna Base MP65, and each one of the mast sections MS-116, MS-117 and MS-118 (or the US-Equivalent types).
    The complete length of the Antenna is about 2,25m
    73,
    Klaus, DL4FCY

  6. Hello Laurent !
    The ideal length of the Antena ist the original antenna: Antenna Base MP-65 and each one of the mast sections MS-116, MS-117 and MS-118 (or US-equivalent types). The complete length is about 2,25m.
    73,
    Klaus, DL4FCY

  7. Hello !
    I am searching for somebody who is VERY experienced in the SEM 25….. Since a couple of weeks my SEM 25 doesn’t transmit anymore. A measurement with the SEP 25 showed missing grid-voltages and tensions in the transmitter, but the Change of the plug-in-modules (Transmitter power supply) was’t succesful.
    The failure is: No Transmission (not on the lower band and not on the upper band), no function of the AGAT, the frequency display of the AGAT is not the same than the frequency selected with the controlbox. the Receiver is working well.
    Does anybody have an idea ?
    73,
    Klaus, DL4FCY

  8. Hello everybody !
    Yesterday I could solve the Problem with my sem 25-transmitter. At least there was 3 Problems, I write them here for everybody who fights the same fight like me…
    Problem 1: Inside the Cable no. 16 (the connection cable between the remote box and the mounting base, the line which transports the “upper-/lower-band-Information to the Transceiver) was broken – I don’t have any idea how this could happen…
    Problem 2 : Inside the relay unit which is located inside the mounting base a relay was defective, or one of the wires’ soldering didn’t have a good contact anymore. The next Project will be to disassemble the complete unit, check again every single relay-contact, and change ALL cables inside the unit, so that I will have a spare unit.
    Problem 3 : The antenna-tuning-unit (AGAT) did not work anymore.
    actually the unit works fine again, but i will make some measure-sessions with my test-box SEP 25, so that the alignment will be optimized.
    Then the next dx-session can come !!!
    73,
    Klaus, DL4FCY

  9. Hi Klaus
    Finally I installed the sem 25 on the MUNGA, I connected the AGAT and the antennas. I connected the instrument for the verification of stationary waves.
    All right, but from 26 Mhz to 30 Mhz the transmitter does not work, then it emits radiofrequency.
    From 30 MHz to 54 MHz I can get a good issue, over 54 MHz the stationary rise considerably.
    Do you have some advice?
    Did I mistakenly mount the antennas?
    Thank you
    73,
    Giovanni IW2BZO

    • Hello Giovanni !
      The first thing I can recommend you is to check, if the frequency you have tuned to the remote-box is the same shown on the AGAT-display. For example: If the frequency you have tuned on the remote-Box is 29,60 MHz, then the AGAT-display (the little “window” on the upper side of the AGAT-unit) must show 29,5 MHz. If you change the MHz-Steps, the frequency displayed from the AGAT must change too. Also very important is the switching when changing from the lower- to the upper band and versa (between 46 and 47 MHz). The “MHz” always mut be the same, on the control-box and on the AGAT.
      Do you have rf-output beween 26 and 30 MHz when you press the ptt ? You can monitor your output-signal on a fm-receiver. Do you use an original antenna (base mp-65 and each on mast-section ms-116, ms-117 and ms-118) ? The AGAT is designed to work with this configuration ! Maybe the AGAT is not correct aligned with the antenna you use between 26 and 30 MHz. Normally the antenna sytem should be aligned once a year over the complete frequency range. Switch a swr-meter between transceiver and AGAT, press the ptt and align the agat for a minimum reflecting power. Repeat this für every MHz-step. Unfortunately, the AGAT is not able to do own measurements an alignments with the antenna (the construction era of the sem 25 with the AGAT is the sixties !).
      I hope this is helpful for you !
      73,
      Klaus, DL4FCY

  10. Thank you Klaus
    the weekend I start to work.
    73 + 44
    Giovanni IW2BZO

  11. Hello SEM-25-Community !
    I have a Problem with my SEM 25, and I could locate it to the interconnect relay unit which is located inside the mounting. The Problem are soldering Points at the relays. If the cables are moved for measuring, the wire can break at the soldering Point, and when the insulation was melted when the solderings was made, it feels as if the solderings are ok – but they aren’t !!! So I removed all cables, and now I want to rebuild them with new cables. When refering to the circuit diagram on this side (made by the Fernmeldeschule des Heeres), I saw that there are differences between this circuit diagram and the circuit diagram in the official Manual (TDv 5820/046-40 Bild 16). Actually I’m checking the circuit diagrams from both sources , Information will follow…
    73,
    Klaus, DL4FCY

  12. Hi Marc !
    I found a relatively complete Version of the german manual for the SEM 25, including circuit diagrams and aligning procedures. If you are interested, I can mail it to you. The size of the Manual is about 25 MB. Can you give me a E-Mail-adress ?
    73,
    Klaus, DL4FCY

  13. I think that my email would choke on a 25M file. Is there any other way that you could share it? Afterwards, I would be happy to host the file here on my web site if you would like.

  14. Hi Marc !
    On the top of this page you wrote about a “SEM 20” – I searched about it, but I couldn’t find anything that such a Radio existed. Can you send me further informations about this set, maybe photos ?
    Many thanks, 73,
    Klaus, DL4FCY

  15. Hello @ all !
    I am very happy to announce that my SEM 25 is working again !!!! I found a defective relay inside the relay interconnect module which is located inside the mounting, the band information cable F inside cable 16 (connection between the control-box and the mounting) had no contact…, and the driver motor inside the tuning unit (AGAT) was defective. Now the radio is working fine again-It’s been a long way…
    IMPORTANT INFORMATION FOR ALL SEM 25-USERS : Be careful when using schematic diagrams from the “Fernmeldeschule des Heeres” !!! In some cases there are differences between this schematics and the schematics from the “official” Manual (TDv 5820/046-40). At all differences I found that the schematics in the TDv are correct !
    I’ve sent the complete TDv to Mark – maybe there is a chance to host it here ?
    73,
    Klaus, DL4FCY

    • Avatar

      Klaus,

      Do you have schematics for the control box/audio here listed as O. I am trying to make a headset with ANR to work but cant get the right combination to get to work perfectly.

  16. Avatar

    Hi,

    I am trying to connect a new head set with ANR to a SEM-25 but I cant get the pins to match. My head set has 7 cable/functions: Speaker +, Speaker -, Mic +, Mic -, ANR, and 2 PTT (one for speaker and one for mic).
    Here is what for a fact it is working: Speaker + with pin A, Speaker – with pin B, ANR with pin E and PTT for speaker with pin F.
    So I am missing MIC + and – and its PTT any thoughts?

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