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KS-30 synthesizer
Digital frequency synthesizer · 2-24 MHz

KS-30 was a digital PLL-based frequency synthesizer, developed in the late 1970s by Heinrich Pfitzner GmbH in Bergen-Enkheim (Germany), for use with the German SP-20 spy radio set. It was intended as a replacement for the crystals, and connects directly to the 20-pin socket at the front panel of the Telefunken S-6800 transmitter, acting as the driver stage (German: Steuer-Sender).

The synthesizer allows any frequency between 2 MHz and 24 MHz to be selected with increments of 1 kHz, and directly produces the transmission frequency. The 20 mW output is fed directly to the transmitter which amplifies it to approx. 30 Watts before passing it on to the antenna tuner.

The image on the right shows a typical KS-30 synthesizer in a military green enclosure. It was also available in a grey enclosure, in which case it was intended for the Stay-Behind use of the radio set. It had a metal rail at either side of the case, allowing the units to be mounted sideways.
KS-30 synthesizer

The KS-30 synthesizer was introduced several years after the SP-20 spy radio set itself, which was initially operated with quarz crystals. The KS-30 was connected to the Telefunken S-6800 transmitter by inter-connecting the 20-way sockets of the two devices. The synthesizer is a critical part of the SP-20 radio set, and many of the surviving examples appear to be exhibiting problems after a shelf life of more than 30 years. Most of these problems can be solved however.

KS-30 synthesizer KS-30 synthesizer Front panel Display muted (dot shown) Frequency shown in display of synthesizer KS-30 with terminator plug KS-30 with terminator plug With front panel removed
All controls and connections are located at the front panel. At the top is a 5-digit 7-segment red LED display that shows the currently selected frequency. A decimal dot separates MHz from kHz. Four push-buttons are used to select the desired frequency by incrementing each unit. To save energy, the display is turned off after a few seconds, leaving the decimal dot ON to show that the device is running. The display can be re-enabled by pressing the lamp button at the far right.

KS-30 front panel with display in stand-by

The image above shows the front panel of the KS-30 whilst power is supplied to the unit and the display is in stand-by mode. Note that the decimal dot of the display is lit. In the image below, the display is re-enabled by pressing the lamp button at the right. Frequency is set to 7.125 MHz.

KS-30 front panel with display enabled

Two 20-pin sockets are present at the front panel. The one on the left is used for connection of peripherals, such as a high-speed morse burst encoder. When no peripheral is connected, a terminator plug should be present in this socket as shown in the image above. The socket at the right is used for connection to the Telefunken S-6800 transmitter. Shown here with the cable.

  • Military version
    The military variant can be recognised by its olive green enclosure. It is connected to the S-6800 transmitter by means of a 1 metre shielded cable with 20-pin SME20P plugs at either end. The full wiring of this cable is given below.

  • Stay-behind version
    The stay-behind variant can be recognised by its grey enclosure. It has a metal rail at either side of the body, allowing it to be mounted sideways to the left side of the (grey) S-6800 transmitter. It is connected to the transmitter by means of a small connection block.
A1 or F1 modulation
The KS-30 has two modes of operation: A1 (CW) and F1 (FSK). A1 modulation is used with the older generation of burst encoders, such as the RT-3. Most military sets were used in this mode. F1 should be selected when using the faster Speicher and the much faster MMP burst encoders.

Most stay-behind sets were used in F1 mode. The desired mode of operation is selected by means of a jumper inside the unit, on board 1.

For this, the case of the KS-30 has to be opened. Remove the single screw at the rear of the case and slide off the case shell. Next, remove the metal cover from the top of the frame by taking out a single screw. The jumper is on the largest board at the top side and is marked Betriebsart (mode), as shown in the image on the right. In the left position, A1 is selected, whilst in the right position, F1 is selected, as in the image.
Mode selector

When using A1, the burst encoder (typically an RT-3) should be connected directly to the keying input of the transmitter, just as it was done before the KS-30 synthesizer was introduced. In this mode, the terminator plug should be installed in the leftmost socket of the KS-30 synthesizer.

When using F1 mode, the fast burst encoder should be connected to the leftmost socket of the synthesizer (instead of the terminator). The encoder uses two hardware lines to control the radio station: the line Auftastung, which enables the transmitter, and the line Tastung, which is used for sending the data in high-speed morse code. Full connections are given below.

Configuration jumpers Configuration numbers (mode jumper removed) Mode selector
Connection block   wanted
With the military variant of the SP-20, it was common practice to connect the synthesizer to the transmitter by means of a one meter cable.

With the stay-behind version of the set however, it was more common to place the synthesizer to the left of the transmitter and connect the two units by means of the small connection block shown in the image on the right [1].
Connection block for fitting the KS-30 synthesizer directly to the S-6800 transmitter. Photograph by Jim Meyer [1].

Burst Encoders
In order to minimise the risk of interception and radio direction finding (RDF), a burst encoder was often used with the SP-20. It allows a pre-recorded coded message to be played back in morse code at very high speed, in order to keep the transmission as short as possible.

The first burst encoder that was issued with the SP-20 was this electro-mechanical RT-3 unit. A small military-grade metal box that allowed a message of no more than 25 characters to be stored mechanically. Once on-air, the message was played back by operating a hand crank.

Later, more advanced burst encoders were issued, such as the GRA-71, MMP and Speicher.

 More information
The RT-3 burst encoder. Click for additional information.

Speicher Burst Encoder
The Speicher (memory) was an electronic burst encoder for sending numbers at high speed in morse code. It was powered directly from the mains and was housed in a similar case as the units of the SP-20 spy radio set.

The Speicher was probably issued in the 1970s to replace the rather limited RT-3. Eventually it was replaced itself by the more advanced MMP.

 More information
Speicher (memory) burst encoder

MMP Burst Encoder
The MMP was a fully electronic high-speed (1200 baud) burst encoder that was used with both the SP-15 and the SP-20 spy sets.

The MMP replaced older devices, such as the mechanical RT-3, the American AN/GRA-71 and the early electronic Speicher. It could hold more than 1000 letters and numbers in its battery-bakced CMOS memory and could send them at various speeds between 15 and 1200 baud.

 More information
High-speed morse burst encoder MMP-B

Block diagram
The block diagram below shows how the KS-30 works. At the bottom right is the digital section with the ÷n (divide-by-n) counter at its heart. The divider drives the display logic and is also in the feedback loop of the Phase-Locked Loop (PLL) circuit that produces a 77-99 MHz signal at its output. This signal is mixed with a modulated 75 MHz signal, that in turn is derived from a TCXO generated 74.97 MHz reference signal, mixed with an FSK modulated signal from a 3 MHz VCO.

At the bottom left is the internal power supply unit (PSU) that converts the incoming 10...15V DC voltage into a stabilized 9.8V for the analogue circuitry and 9.5V for the display logic. An extra stabilized 7.5V rail is provided for the 3 MHz VCO and its buffer amplifier. The keying logic, at the top of the block diagram, can be configured for FSK (F1), in which case jumpers are used to select the desired frequency shift, or CW (A1), in which case the VCO modulator is bypassed.

Getting access to the interior of the KS-30 is extremely simple. Just remove the only screw from the rear side of the case and slide away the case shell. This reveals a metal frame that is mounted to the front panel. All electronics are housed inside this frame and behind the front panel.

Some of the digital ICs are located behind the front panel. They are used for scanning the keyboard and driving the LED display. The actual synthesizer and the analogue electronics are located inside the frame. After removing the lid from the frame, six compartments become visible, as shown in the image on the right.

A total of 6 printed circuit boards (PCBs) are located inside the silver-plated compartments of the frame, whilst the largest one (board number 3) is located at the bottom. In addition, three stacked PCBs are mounted to the front panel.
Interior - top view

The image above shows the interior of the KS-30 synthesizer after removing the lid of the compartmented frame. It is attached to the front panel by means of two screws at either size and can easily be removed. The front panel is connected to the digital board at the bottom by means of a 27-pin header, whilst a separate teflon coax wire is used for the 20mW RF output.

With cover removed KS-30 without cover Interior Interior - top view Interior - top view Interior - top view Top view With front panel removed
Bottom side (board 3) Bottom side Board 3 partly removed from the frame Board 3 Board 3 (digital board) at the bottom Power supply Reference oscillator Configuration jumpers
The boards are numbered as follows:

  1. PLL, keying logic
  2. VCO
  3. PSU, TCXO, prescaler, counter, memory
  4. Multiplexer
  5. Display
  6. Mixer
  7. Filter and amplifier
  8. 24 MHz filter
  9. Output amplifier
  10. Keyboard

Note that boards 4, 5 and 10 are fitted behind the front panel as a sandwich of three boards, and that the largest board (board number 3) it at the bottom side, in the position as shown above. This board holds all digital parts, the power supply and the reference oscillator. It is connected to the analogue parts via a series of feed through capacitors in the frame. The front panel connects to board 3 via a large 27-pin connector. The image below shows the position of board 3:

The synthesizer is one of the most critical parts of the SP-20 radio station. It contains a mixture of analog and digital parts and is difficult to align. Due to aging of the components it is very likely that a surplus KS-30 no longer works (correctly) after a storage period of more than 30 years.

  1. Solder case of reference crystal to ground
    The 74.97 MHz refrence crystal on board 3, appears to be picking up a lot of noise from the surrounding circuits, resulting in a high level of phase noise in the output signal. Although the crystal is held in place by a wire bridge that is soldered to ground, this bridge does not make proper contact with the casing of the crystal. It is advised to solder the head of the crystal case directly to the ground plane of the PCB.

  2. Replace 10nF capacitor by 10nF + 10µF
    The quality and value of capacitor C19 on board 3, is insufficient to effectively eliminate phase noise caused by power rail noise. It is advised to replace C19 by a high-quality 10nF capacitor. When doing this, it is advised to add a 10µF (ceramic) capacitor in parallel (use an SMD variant, so that it can easily be added at the solder side of the board).

  3. Add 10µF
    In order to further reduce noise on the power rail, add a 10µF ceramic capacitor to board 3, between the top of R19 (the supply rail) and ground. This should reduce any feedback from the +18V generator that is built around V05 and V06.

  4. Check 5V1 Zener Diode (D20)
    The 10V rail is divided into two 5V rails by using a 5V1 zener diode to drop down by 5V. This is done to allow the 11C90 pre-scaler to be powered by -5V. To prevent unnecessary dissipation, half the digital ICs are connected to the upper 5V rail, whilst the other half is connected to the lower 5V rail. This is possible as most signals are AC-coupled.

    Due to the high rush-in current of the 11C90, the voltage on the lower 5V rail is briefly driven at a much higher voltage, which potentially causes some of the ICs to latch-up. Once an IC is in latched-up state, it will draw too much current, causing damage to the 5V1 zener D20. Check the condition of the diode and replace it if necessary.

  5. Add safety 6V2 Zener Diode
    To avoid the above problem, it is wise to add a 6V2 zener diode between the 5V line and ground. This prevents the voltage to the digital ICs from going above 6.2V when turning the device on, and avoids a possible latch-up in any of the digital ICs.
6V2 zener added between the 5V rail and ground 10F capacitor in parallel to C19 10F capacitor added between the top of R19 and ground Case of the reference crystal soldered to ground Test cable Test plug
The table below shows the pinout of the leftmost socket as seen from the front of the synthesizer. This socket is used for connection of peripherals, such as a morse key or a high speed morse burst transmitter, like the the Speicher or the MMP. If the socket is unused, a terminator should be installed.

  1. n.c.
  2. Loop 1 1
  3. Loop 1 1
  4. n.c.
  5. GND
  6. Loop1 1
  7. GND
  8. Loop 2 1
  9. Loop 2 1
  10. 10...15V
  11. n.c.
  12. Loop 2 1
  13. 10...15V
  14. Tastung 3
  15. n.c.
  16. n.c.
  17. Auftastung 2
  18. Tastung 3
  19. n.c.
  20. Auftastung 2
The table below shows the pinout of the rightmost socket as seen from the front of the synthesizer. This socket is used for connection to the transmitter. The loop wires shown in the drawing reflect the internal wiring of the socket, as given in the original circuit diagram [B].

  1. HF
  2. Loop 1 1
  3. Loop 1 1
  4. HF
  5. GND
  6. Loop 1 1
  7. GND
  8. Loop 2 1
  9. Loop 2 1
  10. 10...15V
  11. n.c.
  12. Loop 2 1
  13. 10...15V
  14. n.c.
  15. GND
  16. n.c.
  17. Auftastung 2
  18. n.c.
  19. n.c.
  20. Auftastung 2
  1. These lines are 'cold' links between the left and right sockets. They run straight from the peripheral to the transmitter and are not connected to anything inside the synthesizer.
  2. In A1 mode, Auftastung is used for the connection of a morse key or a medium-speed burst encoder. The line Tastung should be grounded, by means of a terminator plug.
  3. In F1 mode, Auftastung is used to enable the transmitter, whilst Tastung is used for keying the data with a high-speed burst encoder. The line Tastung is only available on the leftmost socket.

Connecting to the transmitter
For connection between synthesizer and transmitter, a 16-way shielded cable is used, with a 20-pin SME20P connector 1 at either end. Two pins of this connector are used for connection of the shield and two other pins remain unconnected. The wiring 2 of this connector, when looking into the female sockets on the devices, is given below. Both plugs are wired identically (1:1).

Wiring of the multi cable bewtween synthesizer and transmitter

A suitable cable with a length of 1 metre was supplied with the military version of the SP-20. This cable is also known as NSN 5995-12-188-3633. A small connector block was generally used with the (grey) Stay-Behind version of the radio set. The latter requires the synthesizer to be placed adjacent (to the left of) the transmitter, so that the connector block can be fitted to both sockets.

  1. This is a military connector made by Winchester Electronics [3].
  2. This is the same as the solder side of the male plugs.

Cable between synthesizer and transmitter Close-up of SME20P plug Looking into the pints of the male plug Disassembled plug Close-up of the wiring of the SME20P plug Short SMB cable Terminator plug
Connecting the RT-3 burst encoder
When using the RT-3 burst encoder, it should be connected directly to the morse key sockets at the front panel of the transmitter (not to the synthesizer). In this case, the KS-30 synthesizer should be configured for A1 mode, and the terminator plug should be installed in the leftmost socket of the synthesizer.

Connecting the Speicher burst encoder
When using a very high speed burst transmitter, such as the Speicher or the MMP, the KS-30 should be configured for F1 mode. The keyer should be connected to the leftmost socket on the synthesizer, rather than directly to the transmitter. The diagram below shows the wiring of the cable between Speicher and the KS-30 synthesizer, when looking into the sockets of the devices.

  1. GND
  2. Tastung
  3. Auftastung
Connecting the MMP burst encoder
Connection to the later MMP burst encoder is similar to Speicher, but the cable has a LEMO plug at the MMP-end. The diagram below shows the wiring of the cable that is used between the MMP and the KS-30, when looking into the sockets on the devices. The line Auftastung is driven by the MMP just before sending the message. It enables the transmitter. Once the transmitter is stable, the actual message is sent via the Tastung line in FSK. Note that the KS-30 should be set to F1.

  1. GND
  2. Tastung
  3. Auftastung
Note that the leftmost 20-pin socket on the synthesizer is not used, but that a terminator plug should be present in this socket for correct operation of the set. Suitable terminator plugs were supplied with each SP-20 radio set. The pinout of the terminator is given above, when looking into the leftmost female socket on the synthesizer. Pins E, H, R and V are connected together.

Terminator plug on the leftmost socket of the synthesizer

  1. Gerätebeschreibung KS 30
    Service Manual of the KS-30 synthesizer (German). 77 pages.
    Pfitzner Teletron, 16 March 1983 (first released July 1977).
     Circuit diagrams at DIN A3 size
  1. Helmut 'Jim' Meyer, HS0ZHK, My way to Ham - Radio and beyond
    Website QRZ.COM. Personal correspondence.

  2. Louis Meulstee, Wireless for the Warrior, volume 4
    ISBN 0952063-36-0, September 2004

  3. Winchester Electronics, SME20P connector
    Visited August 2016.

  4. Günter König (DJ8CY), Hint and tips about the KS-30
    Personal correspondence. August 2016.
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Crypto Museum. Created: Monday 29 August 2016. Last changed: Friday, 15 December 2017 - 08:52 CET.
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