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.