Spy radio
Burst encoders
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High-speed morse burst encoder - wanted item

The Speicher was a fully electronic burst encoder that could send numbers in morse code a very high speed. It was developed around 1974 in Germany. Speicher was developed for the SP-20 and replaced earlier mechanical burst encoders, such as the NATO-issued RT-3 and the American GRA-71. In the Netherlands, it was also used in combination with the earlier FSS-7 spy radio set.
Speicher is the German word for Memory, which perfectly describes its function. The unit is housed in a grey case that is similar to the cases of the SP-20 spy radio set. It is powered by an internal battery that can be recharged by a built-in power supply unit directly from the AC mains.

At the right of the front panel are the sockets for the transmitter (key output) and the 110V or 220V AC mains. At the left is a recessed MODE selector and two push buttons, marked START and CALL. The MODE selector has four settings: OFF, REC, SBY (standby) and PLB (play-back).
Speicher (memory) burst encoder

At the top is a small recessed keypad with 12 buttons. Ten of these are for the numbers (0-9) and the two remaining ones are marked G and F. Just above the keypad is a small window with five red LEDs that are used for counting the number of characters in a five-letter group.

The Speicher was probably developed only for the (grey) stay-behind version of the SP-20 and was to be used instead of the earlier mechanical RT-3 burst encoder. It has not been found with the (green) military version of the SP-20. Evidence of the use of Speicher in combination with the SP-15 spy set was found in The Netherlands, where it turned up in the only known surviving SP-15 Stay-Behind container. This container is now in the collection of Museum Jan Corver [1].

In the early 1980s, the Speicher was replaced by the more versatile MMP burst encoder. It was capable of sending both letters and numbers in morse code at a variety of speeds, ranging from 15 baud to an impressive 1200 baud. Some Speicher encoders remained in service however. At present, the manufacturer of Speicher is unknown, but given the extremely good built quality, it is likely that it was a high-end electronics manufacturer like H. Pfitzner or AEG Telefunken.
Speicher with protective rubber cover Speicher (memory) burst encoder Top view Controls MODE selector and start button Connections Speicher mains cable Speicher data cable (to keyer)

All controls and connections of the Speicher are at the front of the unit. The 110-220V AC mains is connected to the small 2-pin socket at the front right. As this socket is smaller than a common 2-pin socket (e.g. the ones that are used on domestic equipment), a standard cable with a modified connector is supplied. The transmitter is connected to the green socket at the right.

The device is operated with the MODE selector at the left, in combination with the START button. When set to REC, a message can be entered on the numeric keypad at the top. This is fully explained below. Speicher has a built-in 6V rechargeable battery (same type as used in the FE-8 receiver) that is charged when the unit is connected to the mains. In SBY mode (standby), this battery is used to retain the message. Setting the MODE selector to OFF, clears the memory.
When preparing a transmission, the text first has to be translated into numbers, as the Speicher is not capable of sending letters. The MODE selector is then placed in the record position (REC) and the START button is pressed to place the memory counter at the beginning (initialize).

The numbers are then entered in groups of five that are separated by a Group Space by pressing the (G) button. The five LEDs behind the window on top of the unit are used to count the number of characters in a group. When all five LEDs are lit, the G-button has to be pressed. This inserts a pause and clears the LEDs. Once the message is complete, the F-button is pressed (Finish).

The MODE selector should now be placed in standby mode (SBY). In this mode the message is retained in memory by the internal battery (or the PSU when the unit is connected to the mains).

Next, connect Speicher to the transmitter, using the special cable that is inserted into the green socket at the front right. The cable shown here was issued especially for the SP-15 spy radio set. Now set the MODE selector to play-back (PLB) and press the START button. This places the memory counter to the beginning of the message and will automatically start the transmission.

Now use the side tone output of the transmitter to monitor the transmission. Once the burst transmission has finished, turn off the transmitter and set the MODE selector to OFF. This clears the memory, even when the PSU is connected or the battery is installed.

Entering a message Entering the 4th digit of a group Front panel MODE selector and start button Output socket MODE selector Modified mains connector Connecting the mains cable


Speicher is housed in a grey painted metal enclosure with the same form factor as the units of the SP-20 spy radio set. It is extremely well-built and contains components that were not commonly available in the mid-1970s. The unit consists of two parts: the front panel with the controls and connections, and the rear part that contains the electronic circuits and the power supply (PSU).
The electronics can be accessed by removing the shell from the rear section, simply by removing a single screw at the bottom of the unit. The shell can the be pulled towards the rear, after which the uper PCB is exposed, as shown in the image on the right. At the rear end (at the left in the picture) is the small PSU and a bay for a 6V re-chargeable battery (which is not present here).

The electronics consists of four PCBs that are connected through a backplane behind the front panel. The PCBs are held in place by a metal frame that is accessible from the PSU end.

After removing two screws at the side of the frame, the hinged rear section with the PSU can be opened like a door, giving access to the 4 PCBs. Each of the PCBs can now be removed by pulling it towards the rear, but precautions have to be taken to avoid damage by static discharge.
The third board from the top contains the actual memory, which consists of 20 CD4061AD chips made by RCA in the US. Each chip has a capacity of 256 bits (64 bytes) and had a price tag of $200 each in 1974 [3]. This means that the 1280 byte memory board holds $4000 worth of chips!

The CD4061AD was introduced in 1974 and was initially only available to selected customers. The chips shown here were manfactured in 1975 [2]. The CD4061 is pin compatible with Intel's 1101 RAM, but consumes much less power, making it ideal for portable battery-powered applications.

The other boards contain various logic circuits, built around RCA's popular CMOS 4000 series ICs. Note the typical zig/zag arrangement of the contact pins, compared to the more common Dual In-Line (DIL) arrangement. The upper board contains the actual keyer and the interfaces to the outside world. The function of each board is printed to the side of the frame (top to bottom):
  1. VCC
  2. Speicheranst.
    Memory driver
  3. Speicher
  4. Ausgabe
Interior Interior Battery socket and PSU Upper PCB Close-up of the PSU Removing the rear frame partly disassembled unit Extracting a PCB
Upper PCB Second PCB Third PCB Fourth PCB Close-up of the ICs LEDs Memory Detail

Speicher and SP-20
Speicher was intially developed for use in combination with the German SP-20 spy radio set that was introduced around 1974. For that reason it is housed in a similar case.

It is likely that it was only used with the grey version of the SP-20, wich was used for stay-behind and clandestine operations (espionage).

 More information

Speicher and SP-15
Although Speicher was originally developed for the German SP-20 spy radio set, is was also issued for use with the older SP-15 sets, such as in the case of the FSS-7 that was used by the Dutch Stay Behind Organisation O&I.

The image on the right shows a Dutch SP-15 set that was upgraded around 1975 with a synthesizer and the Speicher burst encoder.

 More information
Dutch FFS-7 (SP-15) set with Speicher burst encoder

Help required
If you know more about this device, or if you have documentation about it, please contact us. Crypto Museum is still looking for a Speicher for the collection.
  1. Museum Jan Corver, Complete FSS-7 (SP-15) set in water-tight container
    Many thanks for allowing us to take detailed photographs.
    Crypto Museum, October 2008, April 2015.

  2. RCA, CD4061A datasheet
    Date unknown (post-1974). Retrieved September 2015.

  3. Ebay user antiquetech, RCA CD4061 Chip Dies CMOS RAM with Artwork Gift
    April 2015. Retrieved September 2015.

Further information

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Crypto Museum. Created: Thursday 08 October 2009. Last changed: Sunday, 31 July 2016 - 08:25 CET.
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