The typical "Kofferaufbau" came configured in different ways for different missions.

This is the SEM-25 radio. It was used in another UNIMOG alongside High Frequency (HF) radios and teletype equipment. The SEM-25 is used for tactical, i.e. local, voice communications with other units such as tanks and infantry. The HF radios and teletype equipment were used for over the horizon communications.

Of late, it is rare to find a radiobox with all of the original radios. For Amateur radio operators this doesn't often pose a problem. Today's ham radios are solid-state wonders. A typical ham rig is not only a fraction of the size of a typical NATO radio, but will also do the job of the several radios originally used in the kofferaufbau. The small radio in the picture is an Amateur radio that covers 1.8 to 148 MHz. Quite different from the 60lb SEM-25 sitting next to it.
The SEM-25 is a short-range tactical FM transceiver that covers 26.00 to 69.95 MHz. It has 11 channels; 10 "programmed" and one "tunable" from the front dial. 50 kHz channel spacing is used giving the SEM-25 a total of 880 channels. With a selectable power output of either 1 watt or 15 watts, this radio was likely used for communications with other field units such as tanks and infantry. The SEM-25 has a "relay" position for use with another receiver (or transceiver) to create a "repeater" system, or it can be hooked up to a field telephone. My SEM-25 came with an AB-15 base and 9 feet of antenna made up of two AB-21, and one each MS-117, AB-23, and MS-118AK antenna sections. No antenna tuner was used with this unit; it was wired directly to the AB-15 base. For more info on the SEM-25, check out Mark's Green Radio Page.

This is an "automatic" antenna tuner unit (ATU) for the SEM-25 radio. "Automatic" in that the unit has tuning settings every 0.5 MHz which are adjusted by tuning screws. Attach a test instument, tune the unit for 26.0 MHz, tune the unit for 26.5 MHz, tune the unit for 27.0 MHz, tune... well, you get the idea. Once set up it is pretty slick. A motor in the ATU brings the correct tuning position into operation based on the frequency the SEM-25 is set to.

The other radio depicted is a Teletron TE-704C high frequency receiver. This unit is designed primarly for receiving facsimile and teletype traffic. It also receives shortwave and Amateur (USB/LSB) broadcasts. The 704C covers 10 kHz to 30 MHz. With 10 Hz selectivity and 0.5 uV sensitivity this 20 year old radio rivals modern Amateur equipment. An ideal receiver for the mog as it works on 24 VDC... or 220 VAC!

For the Amateur Radio operator, the radiobox is ideal. Each June U.S. and Canadian hams participate in "Field Day". This is a contest in which hams attempt to contact as many other hams as possible in a 24 hour period. The contest emphasizes working under emergency conditions, i.e. in the field. Ham groups often set up their radios on hilltop sites or in public places such as school fields. Designed essentially as a mobile command post, the UNIMOG with a radiobox is the ultimate for Field Day.

Send comments and mail to
Ed Wright, kb6tho@mraradio.org
Copyright 2001 The Mountain Repeater Association
Last updated by Ed, KB6THO on 2/7/01