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!




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”.





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




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




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



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)



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





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 (?)



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!

Radio tuner (tune + apparatus)
Radio tuner section (tune + part)
Addition stage
Drive, driver, motor
Component carrier
Control head
Block diagram
On-board battery
Intercom (on-board + amplifier)
Part, component
Receive or receiver
Output stage
Balanced (i.e. “balanced line”; literally, “ground-free”)
Frequency synthesizer
Mounting (base + plate)
Radio frequency (RF)
Channel selection
Line, wire
Line, wire
Common, ground
Mains power adapter
Audio frequency
Test meter
Squelch (noise + stop)
Relay, retransmit
Servo amplifier
Servo amplifier
Power supply
Transient protector
Driver stage
Divider stage
Input stage
Intermediate frequency (IF)



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. Avatar

    You have a very nice info site for the SEM-25! Thanks for your efforts. I have a couple of SEM-25’s and a couple of SEM-35’s, and a Unimog radio truck in which they were original equipment.

    One remaining mystery for me is how the antenna tuner knows when there is a match with the radio channel. Any thoughts?


    Bob WB4ETT

    • Thank you!

      I have not actually connected my antenna tuner to my SEM-25 yet… they’re sitting in various piles in the garage until I get around to playing with them again. That being said, I think that the tuner works about the same way as the MX-6707 tuner for the AN/VRC-12 series radios: It’s not an automatic antenna tuner that tunes until it finds a match. Instead, internal adjustments define the matching network to be used for each range of frequencies, assuming that the standard whip is installed. The radio tells the tuner which frequency range it’s in, and then the tuner selects the fixed matching network for that range. If the tuner is out of adjustment, or a nonstandard whip is installed, or possibly even if the antenna is installed in an unusual way, then the tuner will happily and blindly adjust to a poor match.

      • Avatar

        Correct Mark! There is a specific measurement box which contains an SWR meter, a dummy load and (most important) three special tuning tools, where you need two to comfortably ajust the Antenna tuner for each 1 MHz step. Just set the radio to XX.50 MHz, open up the two screws on top of the ATU, srew in the special tools and adjust for that frequency point for minimum SWR while transmitting. What is interesting to me is that there is a diode detector in the ATU to measure the voltage at the antenna, which is neither used by the SEM25 nor the measurement box.

        Gregor, OE1GLC

      • Avatar


        • Hi! I have never changed any of the internal adjustments in my SEM-25. I wrote this page about 15 years ago, so my memory may be wrong, but I think that my list of those settings is just a translation of the German markings that I found inside the radio into English. I would guess that R13 and/or R26 might affect the mic gain? I don’t know how to adjust the deviation, or if there is an adjustment for that.

          Maybe somebody who knows more about adjusting the SEM-25 will see this and reply with better information?

          I am sorry that I’m can’t be more helpful right now. Good luck!

        • I just looked at the modulator amplifier module schematic, and I would guess that R13 is probably a microphone gain adjustment. If you experiment with any of the settings, make sure that you note the original settings before you change anything!

          • Avatar

            thanks for response mark, 73 !!! hear from you soon

            • Avatar

              Hi, looking in the manual it seems like ther is a Audio limiter adjustment (R26) in the modulation amplifier, and the Audio amplifier adjustment R13. According to the manual, R26 is adjusted at 1,25V (effective?) sinewave input at 1kHz for 15kHz maximum FM deviation. Prior to this, R13 is adjusted for 10,5 kHz deviation at 250mV input level, again for 1kHz.

              I assume you want to reduce the FM deviation for Ham use, so you may pick lower deviation values. But keep in mind, that for RX the SEM is still designed for rather broadband FM.

              R36 is the squech setting, I guess setup is selfexplanatory. R5 just sets the audio level for received audio, I guess this is important when all the audio tank communication acessories are used.

              73 de Gregor, OE1GLC

  2. Avatar

    Sorry for my English…

    I have the German version of the LS-166/U and, at least on the earlier versions it seems to contain exactly the same internal parts as the US one (even the speaker elements etc seems to hawe been made in United States. ) , in fact i think it IS the same and possibly even made in US, only differense i can point my finger on is for example that the text abowe the switch is written in German language instead of US (but even parts of the text is the same for example; Lautsprächer-Loudspeaker =LS in both languages osv… So even the military name will be exactly the same as in US in written form. ). The specifications also seems to be the same: 8/600 Ohm osv. Later version (at least the one i hawe) seems to contain a bit more modern parts, i dont know if the speaker elements in later wersions are still made in UnitedStates or if they are made in Germany. But the specifications are still the same as US standard here, 600/5 Ohm (it seems like it has changet from 8 to 5 ohm in the direct mode with later speaker elements (however, that one not the old U model so it´s possible other reasons why the internal resistans differs slightly in the specifications)). The old version i hawe has internal speaker element made by Academy but the later one i hawe is made by A. S. C.

  3. Avatar

    Hi SEM25 community!

    Is there anyone out there who ever tried to remove the transmitter module (“T” in the above picture) from the “Bausteinträger” (main chassis)? I just wonder if I have to remove the transmit servo first, and how difficult it is to achieve the synchronization afterwards. I tried to loosen the 5 screws holding the transmitter module but the thing did not really move.

    (My current project SEM has a broken trimmer capacitor C47, so the lowband TX does not work. The initial fault may have caused some military repair technician to “tweak” all TX trimmers before giving up on that project, and he obviously destroyed C47 on that job..)

    Regards, 73

    • It has been a very long time since I have opened up my SEM-25, but I don’t think that I have removed that module. I don’t think that the “T” or “U” modules pop out easily like the other modules. I hope that somebody with more experience will post a reply.

  4. Avatar

    Congratulations on your page.
    I have in my collection a German SEM-25 radio, which is now working.
    Got it repaired using schematic diagrams of your page.
    Thank you for providing the schematics.

    Forte 73 PY3CE of Brazil.

  5. Avatar

    Mark i reve a service maual for SEM-25 in german in digital pdf.
    You an a copy ?i sendi one copy four you an e-mail.

  6. Avatar

    Good night Mark.

    This is the link you can access to download directly from the web, the service manual SEM-25 Radio.


    73 PY3CE

  7. Avatar

    Hello from Germany !
    Very interesting site !!! Many thanks and congratulations !!!
    Unfortunately it is very difficult to get the technical manual about the sem 25 (and others). The only manual I have is the common description of the set. Much of the things about the sem 25 I know today I learned in the army many years ago, where we used this radios, and circuit diagrams I’ve got from a ham I met at the HAM-Radio in Friedrichshafen. There are some parts in the radio which can be changed very easy (for example the plug-in modules and the tubes), and others which were made for never to be touched (for example the tuning section), in which are so many mechanical parts that it will be a problem to put them together when they’re removed….so that it works.
    If somebody of you can buy a Transmitter-Receiver-Testset (Sendeempfänger-Prüfgerät “SEP SEM 25”), USE THIS OCASSION !!! It makes it much easier to locate Problems or to adjust the radio.
    Klaus, DL4FCY

  8. Avatar

    Mark I have a problem in my SEM25 only transmits on frequencies below 46.95 MHZ you know what can star going on?
    These frequencies normally but transmits in frequencies above 46.95 does not transmit.
    Thank you for your attention

  9. Avatar

    Hello Cristiano !
    Many times ago I had the same problem, but it was very easy to fix (in my case):
    In the Control Box ( Funk-Bediengerät) is a switch that switches between the lower band (26,00 – 46MHz) OPEN and the upper band (47-69 MHz) CLOSED. I hope you have a schematic diagram-it is S2 near the MHz-Switch. If the switch is not correctly mechanicly adjusted, it doesn’t switch if you change between the upper and the lower band , so that you can only use either the upper band or the lower band-depending if the switch is OPEN or CLOSED. In your radio the switch should be CLOSED so that only the upper band can be used. You can find the switch very easy in the opened Control box. If the switch is damaged, it can be changed easy, because the type of switch is a “normal” type.
    I hope this will help to make your SEM 25 work!
    Klaus, DL4FCY

    • Thank you for responding, Klaus! I did not know how to help Cristiano, because I have not done any repairs on my SEM-25 yet.

    • Avatar

      Hey Christiano,

      if the suggestion from Klaus does not fix the problem, be aware that the transmitter uses mostly separate tuned circuits for the upper and lower band. there is a big motorized switch in the transmitter compartment, which does handle these two bands. Take a look at the switch first: If zou toggle between upper and lower band, do all switch wavers move? I had some issues with a broken switch waver once. If the switch is ok, one of the tuned circuits could be faulty as well (less likely).

      Good Luck

  10. Avatar

    hello friends, you can direct me to me, where is located the switch?

    • Avatar

      Hello Ignazio, hello Cristiano !
      If you open and look into the control-box SEM 25, the band-switch S2 is located near the MHz-Selector (the upper level is marked “S1B”) under the cable-bundle which runs on the right side of S1B. In my control-box S2 is a 1SX1-T type. It is fixed with 2 Screws with which the switch can be adjusted to work fine.
      Between the MHz-Position 26 and 46 MHz (Unterband) S2 is OPEN and between 47 and 69 MHz (Oberband) it is closed. With a Multimeter it is easy to measure if the switch is open or closed, and also the adjustment is easy.
      I shot a picture, but unfortunately it’s not possible to make a attachment to this answer….
      I think this should be the first step you should make before open the transceiver !
      Klaus, DL4FCY

  11. Avatar

    Hello friends’ll check all the possibilities, and also this switch after getting correct ploblema make available here the repairs made,
    I thank the attention and support of all. 73 PY3CE Military radio collector.

  12. Avatar

    hello klaus, send me the photo of: iz8jjg@hotmail.it
    Thanks, I look forward

  13. Avatar

    Hello Klaus, checked the switches on the front control compartment.They are working properly.
    In the servo compartment engines MHZ servants and KHZ servants are acting correctly.
    However it only transmits to the frequency of 46.95 MHz to make the move to 47MHZ already does not transmit more.
    If you tever more som point I can check will be grateful.

    73 PY3CE.

  14. Avatar

    Hello Cristiano !
    The OB/UB-switch is inside the control-box, and it is switching, when you change the MHz-Selector from 46 to 47 MHz and versa.
    If you send me your E-Mail-Adress, I can send you Pictures I shot from the switch.
    A short additional check to see, if the OB/UB-switch works correctly: If you have the original antenna-tuner (AGAT): On the front of the tuner is a little window which shows the “MHz” which the Trcvr is switched on. If the AGAT is connected to the SEM 25 (the coaxial cable and the antenna is here not neccessary, but the control cable (#10)), in the window you can see the MHz-Position you have selected on the control-box. And if you change this frequency from the upper band, the MHz-Frequency in the AGAT-Window will also change. If not, then the OB/UB-switch doesn’t work.
    Klaus, DL4FCY

  15. Avatar

    Hello Klaus my e-mail Is: py3ce@yahoo.com.br


  16. Avatar


    Mark maybe you can help me with another question.
    I bought it for my collection a transmitter equipment VOR model 485A manufactured by Wilcox Inc, USA
     It has been disabled here in Brazil.
    I want to restore it, but I have no schematic diagrams or service manuals you could help me figure out where I can get it

  17. Avatar

    Is it possible to retune the SEM25/35 and/or the AGATE to go up to 73MHz?

  18. Avatar

    Hi Marc, Hi Howard !
    I don|t have any idea if its possible to modify the sem 25 for 73MHz… sorry
    73 de klaus dl4fcy

  19. Avatar

    hello dear friends, you know show me how to align the frequency tx-rx 25 sem?
    my sem 25 of the 11 mt., listen to me better to 27,351
    thanks aspect your answer.

  20. Hello Ignazio !
    The SEM 25/35 changes frequencies in 50 kHz-Steps, so that it should work also on 27,35 MHz (with a tuned antenna). The difference of 1 kHz to 27,351 should be in the frequency accuracy the system can realize.The receiver crytal filter width is 30kHz (6dB), so that it is possilble to receive stations who works on 27,351 HMz.
    If this is not possible, maybe the most simple solution would be for the other stations you want to work to qsy on 27,350 MHz, hi ;-)
    Klaus, DL4FCY

  21. Hello, thank you for your great page! Does somebody has an idea (or experience) to connect a SEM 25 to a public telephone line?

    There was some CB radios who did it! And I have seen that the SEM 25 has a plug # 17 (dummy plug?) on the basic plate, right side, beside the plug # 52.

    I have seen on Amateurtele.com a description “17: aansluiting van/naar 600 Ohm telefoonlijn.” = “Connection from/to a 600 Ohm telephone line” and that is exact the resistance between La and Lb in a public switched telephone network.

    Does somebody knows something about that? I appreciate your support in advance. …et vy 73 to all OMs :-)

  22. Avatar

    Hi folks!

    I`m adjusting and trying to receive/transmit with my SEM 25. Sometimes my channel-switches (knobs no.E and F) do not hit the MHz . It sounds like a little engine is sliding inside the set. When I turn the radio off and restart it, it will function. Is it normal? Is it because my batteries are low?

    Trond in Norway.

    • Avatar

      PS.: I`m tuning in the area 27.oo – 27.95 MHz area. At the moment I`ve succeeded in receiving good – very good signals from Germany, Great Britain, Spain, Italy, Finland and Eastern Europe. My antennaes are vertical dipol , inverted V – dipol and the simple 1/4 – military antennas.
      Your page is great! Trond.

  23. Avatar

    Hell all,

    I just bought a Willys M38 a1 on with a “fonctional” SEM25 is mounted. Unfortunately I have no idea how to operate this sem25. I got a complete German manual delivered with it. But my German is not that good.

    Does anyone know if these SEM 25 are still being used? By who? and how?


  24. Avatar

    Hello . I have one Sem-25 and one Em-25 , can I plug two BNC (em+sem) on only AGAT ? It’s for use in relais position . Best regards

    • I do not think that would be a good idea. With both the SEM-25 and EM-25 plugged into the same antenna, the EM-25 would see far too much RF power on its antenna input when the SEM-25 transmits. Also, having both radios connected to the same antenna would mess up the impedance matching.

      If I remember correctly, the EM-25 uses a simple whip antenna, so you would not need a second antenna tuner for it.

  25. Avatar

    Bad idea. Transmitting on the SEM would basically kill the front end of the EM!

  26. Avatar

    Also, if you are going to use it for relay ensure the tx and rx frequencies are sufficiently far apart to avoid desensing the EM. Ifeally you should have some filtering external to the radios and before the antennas. Having the antennas as far apart as practicable is also a good idea. It all really depends on the frequency difference.

  27. Hello to all !

    In the original SEM 25-Manual (TDv 5820-045-12) is a wiring diagram which shows all possible parts of the SEM 25-System. It shows that a additional Receiver EM 25 can be connected to the Antenna-Tuner SEM 25 (AGAT).
    Sorry, I didn’t try it by myself yet.
    The circuit of the antenna tuner can be downloaded on this page.
    Klaus, DL4FCY

  28. Avatar

    Ok , but AGAT have 2 BNC enter , number 14 and 15 . Connector of SEM is 14 connector of EM is 15 . The EM is not concepted for use with whip antenna but with an AGAT . My question , why 2 BNC connector in AGAT ? One for EM and one for SEM . Sorry for my english . Best regards , laurent

  29. Avatar

    Thank’s . But the AGAT is concepted with two enter BNC , enter number 14 and 15 . The 14 is for SEM and 15 for EM . The EM-25 is not concepted for use with whip antenna but with AGAT . In my SEM-25 the BNC is plug number 14 and I plug the wire on the number 14 in the AGAT , for EM-25 is the 15 . My question , why two BNC enter on the AGAT ? Sorry for my english . Best regards , laurent

  30. Hello again !

    You can connect both Radios to the AGAT – the SEM 25 AND the EM 25 (BNC Jack #14 —> SEM 25 and #15 —> EM 25). When transmitting, the relay inside the AGAT disconnects the EM 25 from the antenna. So in this time it is not possible to receive with the EM 25. Of course it is possible to operate the EM 25 to an external antenna (for example an additional Whip).
    Klaus, DL4FCY

    • I stand corrected! Thank you for posting. So, I gather than for relay operation, a separate antenna for the EM 25 would be necessary. But for simply monitoring a second independent channel with the EM 25, one antenna can be shared thanks to the relay in the AGAT.

  31. Avatar

    Ah. Well that does make a difference! Presumably though there still needs to be a reasonable difference between rx and tx frequencies?

    • Hello Howard !

      If you want to use 2 sets SEM 25 as a relay-station, the difference between rx- and tx-frequency must be 10% or more.
      Klaus, DL4FCY

  32. Avatar

    Good morning to all
    Congratulations to the forum fot the insight to the matyer.
    I look for some cables cause the sem-25 I have are not functional
    I look for cables No51 and No10
    Any help?
    Many thanks in advance.

  33. Hello Dimitris !
    The cable #51 is only neccessary if you are operating 2 sets SEM 52 together (for example as a relay-station), the cable #10 connects the antenna-tuner-unit sem 25 (AGAT) to the transceiver sem 25. From time to time this cable #10 is available at http://www.helmut-singer.de and/or http://www.bw-schmitti.de .
    Klaus, DL4FCY

  34. Avatar

    Many thanks Klaus,

    I m looking for buying these cabkes.
    Any help?

  35. Good evening at All SEM25 fans.
    My name is Giovanni and I have a SEM25 and a EM25 with a AGAT.
    I need help from those who are more experienced than me.
    I connect everything according to schema, the SEM engine works but the AGAT stays motionless.
    Turning on the transmitter, the AGAT rotates in full scale and does not move anymore.
    The transmitter works, verified with its ros-meter, and the loudspeaker on some frequencies receives signals.
    I checked the connection cables with the tester and they are all working.
    Can someone help me?
    Thank you from Milano

  36. Hi Giovanni !
    When changing the kHz- frequency on the control-box only, then the frequency displayed on the AGAT will not change. If the frequency on the control-box is changed in MHz-steps, then the AGAT-Display should Change. If not, please check the cable #10 which connects the AGAT with the Transceiver-unit.
    Klaus, DL4FCY

  37. Hi Klaus,
    thanks for your answer.
    Unfortunately, the AGAT does not change both the kHz and the MHz controls.
    If you manually rotate the circular frequency scale in the AGAT by switching on the transmitter, the scale will rotate to full scale and stop.
    I’ll check pin to pin cable # 10.

  38. Avatar

    Has anybody an idea on which frequencys transmittions is done usually.

    I have an old Wollys Nekaf with a build on SEM 25 but I have idea on which frequentie to check. As I’m living in Belgium, I have neither an idea how far the transmittion will work and who I might contact, but it is just for fun. My sem25 should work, but I only hear some static.

    Kind regards,, Erwin

  39. Hi Erwin,
    In Europe the amateur bands that can be used with SEM are:
    10 meters (28,000 to 29,700 kHz);
    6 meters (50,000 – 52,000 MHz) – also called 50 MHz band.

    However, check the Belgium frequency plan and if you need some license.

    Giovanni IW2BZO

  40. Hi Klaus,
    Thanks to your instructions I checked all the cables.
    Cable no. 3 did not make good contact.
    Disassembled, cleaned and reassembled, everything works perfectly.

    Shortly, I set up the equipment on a MUNGA and I will try to calibrate the AGAT.
    Thank you
    Giovanni IW2BZO

    • Avatar

      Giovanni! When serving in the Norwegian army , I used the SEM-25. IF something did not work, we checked and cleaned the cables. Especially earth-conections were checked (Bad climate). After that, everything was ok. Once a Leopard 1a was drowned in a bog. After 48hours, the tank was saved and the cleaning-work started. I remember that the radios (SEM-25 X2) still worked flawlessly!!!!

  41. Avatar

    Hi Giovanni !
    Thanks for the info !!! For the alignment of the AGAT you need special tools which are included to the Antenna check Box (in German: Antennen-Prüfgerät). Without them it will be very difficult to adjust the “C” and the “L”-Pins.
    Klaus, DL4FCY

  42. Hi Klaus,
    I have the tool, but I have no instructions.
    I assume that for each step I have to act on the adjusting screws, until you get the lowest reflection.
    Then, hope that there is someone listening…………
    Giovanni IW2BZO

  43. Avatar

    Ciao Giovanni !
    Here are the instructions: Connect the antenna testing instrument or a swr-meter between SEM 25 and AGAT. Select the frequency you want to tune on the control-box of the transceiver. In the display of the AGAT the frequency (MHz) should be the same (for example: selected Frequency on the control-box SEM 25: 29,60 MHz., displayed frequency on the AGAT-display: 29 MHz). Then press the PTT an read the swr. If it is to high, open the 2 screws which are marked “L” and “C”. For ever MHz-Position there are 1 Aligning Pin “L” (= inductance tuning) and 1 Alingning Pin “C” (= Capacitance Tuning). Now hold the PTT pressed and insert the aligning tools in both holes and turn the tools alternating until the swr is low (or the reflected power has reached a minimum). This procedure must be repeated in every MHz-position you like to work. When I was in the Army many years ago, this was a job for a complete day… 26-69 MHz are 43 positions…
    I hope I could help you.
    Klaus, DL4FCY

  44. Thanks Klaus for the information.
    I think I will have to take it very calmly and patiently!
    At the end, also I put in the EM25 function to check if the SEM transmits ……. and I’ll let you know.
    Giovanni IW2BZO

  45. Avatar

    Hi Giovanni !
    I’m looking forward for your informations !
    I don’t know on which frequencies you want to use the sem 25, but I think on 10m. There are only a low number of channels which can be used. If the conditions are good, you will receive some stations on 29,50 or 29,60 MHz. I use my SEM 25 on these frequencies as a monitor – if there are stations, the condx are good, so it makes sense to look for other stations on 10m on the ssb or cw-segments as well as FM. I use a indoor antenna for 10m with my SEM 25 with a manual Tuner (YAESU FC-700), so the tuning procedure is much easier and quicker than with the AGAT.
    Klaus, DL4FCY

  46. Hi Klaus,
    thanks for the information.
    Giovanni, IW2BZO

  47. Hello, I have two sem25 and two sem35, one with its base for vehicle!

    I also have the antenna base with its box coupling but I no longer have antenna strands MS116, MS117, MS118. Can you tell me where to get them?

    thank you



  48. Hello Baudouin !
    Please refer http://www.helmut-singer.de and/or http://www.bw-schmitti.de
    From time to time they’re offering these parts.
    Klaus, DL4FCY

  49. 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


    • 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.
      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…
      Klaus, DL4FCY

  50. 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 !
    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…


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

  52. Avatar


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



  53. 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
    Klaus, DL4FCY

  54. 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.
    Klaus, DL4FCY

  55. 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 ?
    Klaus, DL4FCY

  56. 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 !!!
    Klaus, DL4FCY

  57. 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
    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 !
      Klaus, DL4FCY

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

  59. 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…
    Klaus, DL4FCY

  60. 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 ?
    Klaus, DL4FCY

  61. 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.

  62. 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

  63. 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 ?
    Klaus, DL4FCY

    • Avatar


      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.

  64. Avatar


    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?

  65. Hello Bruno !
    You can find the schematic diagram of the control-Box in the upper Part of this page (Schematic Diagrams –> Sch12.gif) – and also the schematic of the audio acessory as the Handset H-33. I think the problem is that you don’t have any power for your ANR-circuit supplied via the U-77-Connector.
    Klaus, DL4FCY

  66. Avatar


    I would like to ask for some information regarding the values of the following components from antenna tuner schematic sch18.gif

    I have two antennae and want to use them for CB27 without the big antenna tuner. I just want to add similar LC external components and tune the antenna to 27mhz.

    I have miniVNA and may fine tune it. I just need rough estimation for:
    C24 – 82pF

    Thank you

  67. Hi Pavlik !
    If you want to use your antennas for 27 MHz only, then, for my opinion, it would make sense to buy a cheap little matchbox for CB-devices, because the bandwith of the antenna is probably to small for working on different channels, if you want to do so. If you only want to work always on the same channel, you can align the antenna for the best swr, and then you don’t need a matchbox.
    The original antenna tuner (AGAT) was developed, so that it was possible to use one antenna für the complete frequency range (26 – 70 MHz). I use my SEM 25 with a manual Yaesu FC-700-Tuner, so I can transmit with my antenna (modified CB-Mobile-Antenna INDOOR) on 10m FM. The AGAT is connected to the SEM 25- Mounting, so I can see if the switched (Control-Box) and indicated frequency on the top of the AGAT are the same.
    Please refer the CB-regulations in your country, because in Germany the last Number of the frequencies for CB always is “5”, for example, Channel 4 is 27,005 MHz. Unfortunately the SEM 25 only switches in 50 kHz-Steps, so that there is a difference of 5 kHz between the selected frequency of the SEM 25 and the correct CB-frequency…
    Klaus, DL4FCY

  68. Avatar

    Hello Klaus

    Thank you for the fast reply. I am intending to use the antennas with standard CB radio, set properly to the country channel list.

    Thanks to the warm weather, I spend some time with the NanoVNA and the antenna.

    from yesterday:
    3 element – https://drive.google.com/open?id=1mLbAtVff_F-SBY951dkwNm-GBGxr6oca
    2 element – https://drive.google.com/open?id=1thoth4Q_eyqYJd7PdXiC9DyGmWBQ8fbx

    3 element PC soft after calibration – https://drive.google.com/open?id=1GoQ7CzmAhY6w-fRzZYyHveISXzG_VN45
    3 element tuned with L to GND and C in parallel. – https://drive.google.com/open?id=1wCJQqwdlCZ0AZo2pT6kZaVKmmuEEktxp

    seems possible to make simple transmatch for CB, just need to dig for some old trimmer caps

    Will post results when the antenna is installed.

  69. Hello @ all !

    Here is a information for all who are searching for mil-rig and accessories: One of the “better sources” for olive-green mil radio-stuff in germany is closed ! http://www.helmut-singer.de in Aachen unfortunately doesn’t exist anymore. For many years it has been a competent supporter for mil-collectors around the globe – not only for hardware – they nearly always had a answer questions round about mil-radio and much more.

    Klaus, DL4FCY

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