Configurations
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SEM 25 / EM 25 / SEM 35 configurations

Two transceivers, one receiver - and a whole lot of options. With these basic building blocks the German army catered for most of it's communication needs. And I still find evidence some of these configurations are still in use, if a printing date as recent as 1995 on documentation is something to go by.

For stand alone portable use the basic SEM 35 is combined with Ergänzungsausstattung 5 (Completion set 5), which contains the backpack, long and short antenna's and handset - but the same SEM 35 can be combined with Ergänzungssatz 3 (Completion set 3) which includes a mounting to be installed in a vehicle, with the cables to hook the transceiver up to the on board electrical system.
Then, two portable SEM 35's can be used for relays, with the Relaisstellenzusatz SEM 35 (Relay Set SEM 35). A switch box, two cables - in their very own bag, so meant for portable use - and the relay is up and running.

The SEM 25 is far too heavy and definitely not designed for portable use. It's always mounted in a vehicle or used stationary - as the existence of the mains power supply indicates. It too can be used as a stand alone system, either with the vehicular antenna or with the Antenne-Standbetrieb SEM 25/35 (Fixed Antenna) that gives a longer range. This antenna can be raised next to the vehicle if the need arises. By the way: the SEM 35 can also use this fixed antenna...

Configurations can get more complex, with up to two transceivers - either SEM 25 or SEM 35 - and an extra EM 25 receiver.

An example of a simple vehicular installation would be the PKW 0,4t - Iltis is the more common name for this light car that holds two persons, when fitted with this radio installation. Either a SEM 25 or a SEM 35, with antenna tuner, extra batteries especially for the radio and a simple control box on the dashboard: the Verteiler NF (Audio Junction Box) serving a loudspeaker and a handset and containing a small amplifier. Tuning is somewhat awkward, as it must be done on the actual transceiver somewhere in the back of the car. Typical configuration for reckon, it would seem.
By the way, up to now I've only found the Audio Junction Box mentioned in the one manual where this configuration was described. It is not a part of the main system as laid out in the system manuals.
So, the fact that I found a a comparable control box for two transceivers recently would seem to indicate that there are also configurations with two transceivers in a comparable vehicle... Neat box actually, with small lights to indicate activity on the receivers.

On the other hand, in a tank a full system would be deployed - two transceivers, one receiver, intercom for all crew members, extercom for personnel outside the vehicle and remote control over field telephone wire. Here one of the design specialities of the SEM 25 all of a sudden becomes very advantageous: the detachable control box. The control box for the SEM 25 can be mounted on the surface of the transceiver - and quite often that is indeed where it is. A very short cable connects it to the main transceiver body and it can be worked right on the spot.
However, there are longer versions of that cable, up to ten meters. This means the control can be located elsewhere - and in some configurations indeed the commander will have his own control for one SEM 25, giving him full access to that transceiver including channel change. The design where the actual S/E Bediengerät can be mounted either on the transceiver or remote is very slick - it opens possibilities in the configuration that I have not found in any other system in this era.

A full system always encompasses a separate audio amplifier, for the intercom system but doubling to hook up the local control box of the remote control set. Also, a Überspannungsschutz (Transients Filter) catering for up to four apparatus and making sure that no spikes will foul up the system is found in the schematics for larger installations. Small ones - like the Iltis - do not seem to bother with this, as in these vehicles power would be rather reliable. Tanks and such of course have heavy electric equipment like the motors turning the turret, fouling up the internal board electrical net with spikes and such.

AGAT

That is the German name for the Automatic Antenna Tuner - and all systems except the basic portable SEM 35 make use of them. Without the AGAT and it's connecting cables the SEM 25 cannot be used. Even the Fixed Antenna encompasses one in the top of the mast, with it's own 10 meter cables. 

Mountings

The Germans seem to use a double system when it comes to mounting. In some cases the mounting is more then just the physical fixture, as with the SEM 25 and EM 25, where the mounting contains electronics crucial to the functioning of the apparatus. Also, if one wants to use a SEM 35 other then portable, the mounting provides electronics and connectors that are needed.

Other parts, like the Antenna Tuner (AGAT) often are found without the shock mounts. And that shock mount is only the half of it...

The basic fixture of German radio related parts of this era is the C-Schiene - C-rails. Two rails that will take bolts with rectangle heads, with normal six-angled nuts on top to actually position the apparatus in place. Widely used in for instance the radio tables of the Unimog, sunken in slits. But also available in different lengths - and different widths! - to bolt to any surface of a vehicle. Thus, it seems, the SEM's are kept in place.

But not only the actual transceivers. The AGAT on it's shock mount is mounted on a C-Schiene - so allowing it to be moved up or down with a turn of two with a wrench. Above the C-Schiene there is a hole in the armour, where the antenna mount can be fixed. So, when this particular antenna is needed, the lid on top of the armour is unscrewed and the mount is placed. Up slides the AGAT, to insure a short as possible connecting wire.
And underneath the AGAT there will be blind connectors for the cables not used whet the AGAT is not in place - to keep them clean and out of harms way. Simple, but well thought out...

However, this also where the system went haywire. Recently I've found some more manuals on actual installations and it turns out that very many vehicles had their own kits to fit the radio or radios. So, there is a plethora of different C-schiene mounts for radios and parts of installations. They are not very complicated, but there's a lot of them. Then it seems all cables were made to measure for each possible installation - their Versorgungsnummer are very regular within each kit. This would defeat the neat logic in the actual radios...

Needed parts for working systems

Without giving attention to the full descriptions of actual configurations I will try to give some details of what one would need to build a working SEM 25 of SEM 35 system.

One transceiver

In order to set up one SEM 25 - or SEM 35 on a vehicular mounting - one needs at least the AGAT with it's cables number 10 and number 14. Number 14 should not be a problem, normal coax with standard connectors will do nicely, but number 10 is the cable that actually controls the tuning of the Antenna Tuner, it must be a proper SEM cable. These cables are manufactured up to ten meters in length, some manuals mention that if needed they may be lengthened up to twenty meters. The longest cables I have found are ten meters, these are part of the Fixed Antenna Set.
The AGAT must be mounted as close as possible to the actual antenna and is connected by a unshielded cable that has no special demands according to the documentation. Do not forget to ground both AGAT and whatever is used to mount the antenna on - like that tank!

With a longer cable 16 - the one hooking up the control box mostly mounted on the actual transceiver - one can actually control the beast from a distance up to ten meters, with full functionality. This cable again can be lengthened up to twenty meters, if necessary.

The audio connectors on the SEM 25 control box - and the rest of the system - are standard U-77. A H-33 handset will do nicely, also speakers can be connected.

Two transceivers

For a two transceiver system one needs another AGAT with the trimmings - sorry: cables.
In order to connect the two transceivers through their mountings, cable 51-52 is a must. However, the standard control box with the SEM 25 does not allow using both sets, it only works for it's own set. So, in order to use both sets - on the frequencies set on the control box - another solution is needed. This can take two shapes:
1) The AFKA - SEM 25/35 Schaltkasten (not yet described elsewhere on these pages) is the simple solution, used in small vehicles. It needs power and connects daisy chain fashion to the second transceiver in the chain through a 51-51 cable. A big switch allows changing from one transceiver to another.
2) Go for the full system, including the Amplifier and Intercom Control Boxes. However, I have never found these Intercom Control Boxes on the market - yet. You would also need the Intercom Amplifier as well as more cabling.
 

One Transceiver - One Receiver

Simpler then the one above - only one AGAT is needed. The EM 25 receiver would be tied in to the AGAT by a cable 15-15.0 Number 15 should not be a problem, normal coax with standard connectors will do nicely.
In order to connect the transceiver and the receiver through their mountings, cable 51-52 is a must. However, the standard control box with the SEM 25 - the same as with the EM 25 - does not allow using both sets, it only works for it's own set. So, in order to use both sets - on the frequencies set on the control box - another solution is needed. This can take two shapes:
1) The AFKA - SEM 25/35 Schaltkasten (not yet described elsewhere on these pages) is the simple solution, used in small vehicles. It needs power and connects daisy chain fashion to the second transceiver in the chain through a 51-51 cable. A big switch allows changing from one transceiver to another.
2) Go for the full system, including the Amplifier and Intercom Control Boxes. However, I have never found these Intercom Control Boxes on the market - yet. You would also need the Intercom Amplifier as well as more cabling.
  

Two Transceivers - One Receiver

The maximum set one can build - I thought for a long time, before I encountered rather rare layouts with even four radios. Again, two AGAT's, one for each transceiver, with the receiver tied in to either on of these.
This time two cables 51-52 are needed to tie in all three apparatus. Also, the simple AFKA solution will not work for three channels, one will have to build a full intercom system.
If a fourth apparatus is to be added, it will however not be part of the intercom system.

Last updated: 26-10-2003 13:49 +0100
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