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FS-5000 RX

The receiver of the FS-5000 is a highly compact unit that can be used stand-alone or as part of a complete radio station. When used as part of the full FS-5000, it is located at the front center of the radio, in between the batteries and the DSU. The receiver is known as E-5000 or E-5000M. It is suitable for the reception of (digital) QPSK signals and for (analogue) USB signals [1].

When used as part of the full FS-5000 radio station, the receiver is fully controlled by the DSU. The RX-frequency is set on the DSU in the Receive-menu (Empfang) and the receiver delivers the demodulated signal to the DSU where the encrypted message is stored.

The image on the right shows a typical E-5000 receiver. At the rear (right in the picture) is the socket for connection to the transmitter. At the side of the receiver is a narrow control panel that is used in stand-alone mode. At the front is a 45° sloped edge with a socket for the earphone.
FS-5000 Receiver

In normal use (i.e. as part of the full FS-5000 station), the receiver is connected directly to the transmitter, from which it gets its power and antenna signal. The receiver is extremely sensitive and even the weakest signals can be picked up easily with a simple antenna. It is suitable for frequencies between 50KHz and 30MHz, albeit with lower sensitivity between 50KHz and 1.6MHz.

In case of an emergency, e.g. when one or more of the other modules have broken down, the receiver can be used stand-alone for the reception of voice and morse signals. In that case the H-bar is used and an earphone is connected directly to the receiver (see below). A telescopic antenna, which is part of the toolkit, can be mounted onto a screw-on terminal on the top.

The receiver in the storage container FS-5000 Receiver FS-5000 Receiver Mechanism for locking the DSU Earphone Earphone connected to the receiver Complete FS-5000 radio station Adjusting the volume

Integrated part
The receiver is intended to be used as an integrated part of the FS-5000 radio station. That means that it is installed in its default position at the front center and that it is fully controlled by the DSU. It is constructed in such a way that its control panel can not be used in this situation.

The receiver has a narrow 45° front panel with a socket for the earphone and a volume control knob. At the left is an adjustment screw that allows fine-tuning of the frequency ±3Hz. Do not alter this setting! There are also two green LEDs on the front panel, marked + and -.

The image on the right shows the complete FS-5000 radio station with the receiver at the front center. The DSU is mounted to its right and mates with the 25-way socket on the right side of the receiver. The small control panel of the receiver is now fully covered by the DSU.
Complete FS-5000 radio station

The antenna socket on top of the receiver is not used in this situation, as the receiver gets its HF input from the transmitter. Although it is not necessary, the earphone can be connected to the front panel of the receiver and can be used for monitoring reception. Note that in this mode, both switches on the side-panel of the receiver must be set to the lower position (300/OFF).

Never alter the setting of the Δf adjustment at the front panel!

Please take this warning seriously. The Δf adjustment has been calibrated at the factory during production of the receiver and is extremely critical, due to the narrow-band nature of VSB-modulation. Various collectors have tried altering the setting and found it extremely difficult, if not impossible, to restore the original calibration.

Stand-alone use
The receiver has been designed in such a way that it can also be used stand-alone. This might be useful in case of an emergency, for example when one or more of the other modules have been lost or are broken. The receiver can then be used for the reception of spoken messages or morse. Please note that German version of the E-5000M has to be modified for stand-alone use.

For stand-alone operation, the H-bar should be attached to the rear of the receiver. It should be connected to the socket that normally mates with the transmitter. Next, a single battery is place aside the receiver and is also connected to the H-bar. The two battery-slots on the other side of the H-bar are blocked in this situation.

A suitable earphone is supplied with the toolkit. It can be connected to the headphones socket on the front panel of the receiver. The telescopic antenna (also in the toolkit) should be mounted to the antenna terminal on the top panel.
Receiver-only operation

Note that the telescopic antenna must be fully seated (i.e. all the way in) before it can be used. The socket contains a switch that is engaged by the threaded part at the bottom of the antenna. The receiver is now ready for use and can be controlled from the small control panel on its right side. In normal use (as part of the full radio station) this control panel is covered. Turn the receiver on with the rightmost switch (marked ON/OFF). The display should now show 00000.

Immediately after switching on, the decimal dot (.) will be visible on each digit in the display. Next, use the two push-buttons to the left of the display to set the desired frequency. First press the button ←f a number of times until the dot is visible only on the digit you want to change.

Then use the f↑ button to set the desired value. Repeat this until all digits are set. Then press ←f again until the warning light to the left of the display goes off. If an earphone is connected to the receiver's front panel, any signal on the selected frequency should now be heard.
Setting the frequency to 07020 kHz

The volume can be adjusted with the black knob on the front panel. In the example photographs we've selected 07020, which is a frequency of 7.020 MHz in the 40m amateur radio band on which you are likely to hear morse code signals from time to time. Note that for voice reception, the bandwidth switch should be set to 3000 Hz.

FS-5000 Receiver H-bar Do not use this side when using the H-bar with the receiver Receiver and H-bar H-bar connected to the receiver Receiver in stand-alone setup Receiver-only operation Earphone
Control panel on the side of the receiver Close-up of the control panel Turning ON the receiver Setting the desired value Selecting the required digit Setting the frequency to 07020 kHz Completing the setting Selecting the wide-band filter (3000 Hz)

SSB Modulation
The transmitter uses a sophisticated technique called Vestigial Side Band modulation (VSB) for the transmission of data at very high speed (2000 baud) through a narrow-band HF radio channel. Although generating a VSB-signal is relatively simple, it requires an extremely complex (and large) decoder at the receiving end. As a result, the receiver in the FS-5000 field station uses Single Side Band modulation (SSB, J2B) to receive single-channel Frequency Shift Keying (FSK) data at 75 baud. The demodulated signal is sent to the DSU which converts it into digital data again.

Communication path between BS-5000 base station and FS-5000 field station

The image above shows how data is exchanged between the base station and the FS-5000 field station. Sending data at the highes possible speed is of the utmost importance in order to minimise the chances of Direction Finding (DF) by the enemy. Receiving data does not require high speed, as the base station is generally located in a remote position, often hundreds or even thousands of kilometers away from the field. It can take its time, and its location is not secret.

Technical description
Although the receiver is one of the smallest parts of the FS-5000 it is the core frequency generating component. It not only produces the various frequencies needed for the receiver itself, but also the frequencies for the transmitter. In fact, the transmitter can not function without the receiver. The block diagram below shows how the main FS-5000 components are connected:

Main components block diagram

The synthesizer inside the receiver produces all HF signals for the receiver and the transmitter, from a 10MHz TCXO that can be adjusted ±3Hz at the front panel. It has been calibrated at the factory and should not be changed. The frequency is controlled by the DSU. From the received USB signal, the demodulator discriminates the 75 baud FSK signal and feeds it to the DSU.

Receiver block diagram

The image above shows a more detailed block diagram of the receiver. Please note that this diagram is an educated guess, as we don't have any technical documentation at present. The antenna input is at the top left and the audio output is at the bottom right. The 1st IF is at 50.2MHz, which is the result of the input signal that is mixed with the local oscillator, ranging from 52 to 80 MHz, using high-side injection. The 2nd IF is at 200kHz which is commonly used in Telefunken designs. After a selectable mechanical filter (300Hz or 3000Hz), a 3rd mixer is used to convert the 200kHz into an audible LF-signal and finally a digital FSK-signal.

Although it looks rather simple from the outsite, the device is in fact a sophisticated high-end superheterodyne receiver, built to the highest EMC standards. The compact case consist of 5 large PCBs plus a smaller daughter card on one of them. It can be opened from both sides.

The image on the right shows the first stages of the receiver, which become visible when the top panel (held in place by 6 bolts) is removed.

At the right is the front-end with the socket for the (optional) telescopic antenna. Only when the antenna is fully screwed-in, a switch mounted to the side of the socket is engaged and the new input is selected. Without the telescopic antenna, the input signal is taken from the transmitter.

At the left is the 1st IF stage at 50.2 MHz, which has a 4-stage crystal filter at its center.
FS-5000 Receiver interior

The rest of the receiver can only be accessed from the bottom. After removing the bottom panel, the solder side of the bottom-board becomes visible. The entire bottom section can be removed by releasing 4 recessed bolts. This gives access to the 2nd IF-stages that are mounted below the front-end. The 2nd IF frequency is 200 KHz for which two mechanical 200 KHz filter are present on the lower board. The upper board contains a Telefunken OEM chip marked TEZ - C 18081 S - 103707. The function of this chip is currently unknown. The boards are connected to the synthesizer which resides in the bottom section.

The bottom board holds the synthesizer, the (simple) control logic and the interface logic. The synthesizer is shielded-off from the rest and connects to the 2nd IF via 4 coax cables.

The image on the right shows the bottom board from which the small daughter card has been removed and lifted. The daughter card contains a canned circuit marked KS 1075 that is located on top of a similar circuit on the bottom board itself, marked KS 1076. The board also contains a 10MHz TCXO that is mounted just behind the transmitter-connector at the right.
Lifting the small daughter card

The two cans (KS-1075 and KS-1076) probably contain purpose-built thick-film circuits for the interfaces, the user I/O and sythesizer control. In the image above, the synthesizer is just visible at the top. At the bottom right is the 5-digit LED display that is controlled by the KS-1076.

Never alter the setting of the Δf adjustment at the front panel!

The RX frequency is controlled by the DSU and can be adjusted between 50 KHz and 30 MHz in steps of 1 KHz. An adjustment screw at the front panel, marked ΔF, was used to calibrate each receiver at the factory. Do not change the setting of this adjustment! It allows a frequency adjustment of ±3Hz and is extremely critical. The two LEDs on the front panel, marked + and -, are indicators for RTTY signals and respond to 1140 and 1240 Hz respectively.

FS-5000 receiver interior FS-5000 Receiver interior Font-end (right) and 1st IF (left), top view. Close-up of the alternative antenna input 2nd IF stage (right) and bottom part (left) Top view of the 2nd IF-stage. At the bottom are two mechanical filters. Unknown chip Connector to the bottom board
Bottom PCB seen from the bottom Bottom board top view Perspective view of the bottom board Bottom PCB with the synthesizer and the interfaces Lifting the small daughter card KS-1076 circuit block KS-1075 circuit block
Modifying E-5000M for stand-alone use
The German version of the E-5000M receiver has been modified in such a way that it can not be used in stand-alone mode as described on this page. This was probably done to avoid problems when using the FS-5000 in the field. The modification locks the receiver in the OFF position and in narrow-band mode (300Hz). Luckily the modification can easily be undone within minutes.

The modification consists of two wire links that are soldered directly onto the rightmost two switches on the control panel of the E-5000. The image on the right shows the solder-side of the switches. The two wire links are clearly visible.

De-modification is easy and can be carried out in a few minutes, using nothing more that a cross-head screwdriver (#1) and a small sharp side-cutter. Remove the 6 bolts from the bottom panel of the receiver. Then carefully remove the bottom panel, but ensure that the folded edges of the copper shield are not damaged.
German modification of the E-5000M, consisting of two wire links on the switches.

Next, locate the corner with the two (red) single-pole double-throw switches, and cut the two wire links indicated in the image above. Be careful not to cut any of the other wires and ensure that the cut-out pieces do not disappear into the body of the receiver. The modification is now undone. Close the bottom panel and replace the 6 cross-head bolts. Then test the receiver in stand-alone mode by connecting it to a single battery using the H-Bar and turning the unit ON.

The two switches at the right edge of the small control panel Cross-head #1 and side-cutter Bottom view of the receiver Bottom PCB seen from the bottom ON/OFF switch and 300/3000 switch, after de-modification German modification of the E-5000M, consisting of two wire links on the switches. Receiver in stand-alone setup Turning ON the receiver

When using the receiver stand-alone, it might be necessary to supply a 14.4V from an external PSU directly to the receiver. This can be done in two ways. If the H-bar is present, it should be connected to the rear of the receiver, as described above under Stand-alone use. If a charged battery is available, connect it to the H-bar and use the receiver as described above.

If the H-bar is available, but you don't have an original battery, the external power source can be applied directly to the two thick terminals of the battery socket of the H-bar. The image on the right shows a simple red/black cable with two special jacks that can be fitted to the power terminals. Detailed images can be found below. Please note that the contact closest to the receiver should be connected to the +14V rail.

Please note that the receiver should be powered by at least 14V (ideally it should be 14.4V), as otherwise the receivers's PLL will not lock.
External power cable connected to the H-bar

If the H-bar is not present, the 14V from the external power source can be applied directly to the complex socket at the rear of the receiver. This socket is normally used to connect the receiver to the transmitter and carries a large number of complex signals and voltages. Here is the layout:

Pinout when looking into the male connector from the rear of the receiver

Connector at the rear of the receiver

It should be possible to modify an existing 37-way D-type female connector to fit the above socket. Remove the unwanted pins and drill out the areas for the 4 large coax connectors. Alternatively, you may create an improvised power cable by using a two-pin female connector soldered to two wires. Note that the 0V wire (black) should go to pin 17 of the connector.

External power cable for H-bar Connecting the external power cable Close-up of the external power cable External power cable connected to the H-bar Improvised power cable for D-connector Placing the improvised power connector Close-up of improvised power connection Improvised power connection for the receiver

Technical specifications
  • Frequency range: 2-30MHz
  • Extended range: 50kHz-1.6MHz (reduced sensitivity), 1.6-2MHz
  • Step size: 1kHz
  • Accuracy: ±1Hz
  • Modulation: USB (J2B)
  • Data speed: 75 baud
  • Synchronisation time: < 300ms at S/N > 20dB
  1. Helmut 'Jim' Meyer, HS0ZHK, My way to Ham - Radio and beyond
    Website QRZ.COM. Personal correspondence. Retrieved June 2008.

  2. United States patent 4,780,884, Suppressed Double-Sideband Communication System
    Filed 13 April 1987. Approved 25 October 1988. Previously filed as 741,026 (3 June 1985) and 835,265 (3 March 1986), both abandonned. Retrieved April 2012.

  3. United States Patent 4,730,345, Vestigial Sideband Signal Decoder
    Filed 4 April 1986. Approved 8 March 1988. Retrieved April 2012.

  4. United States Patent 5,663,773, Demodulator for a Complex-Value VSB Signal
    Filed 20 November 1995 on behalf of ANT Nachrichtentechnik GmbH, Backnang (Germany). Approved 2 September 1997. Retrieved April 2012.

  5. Prof. Dr.-Ing. Dietmar Rudolph, Einseitenband & Restseitenband Modulation
    TFH Berlin - Telekom TT - IBH. (German) Date unknown. Retrieved April 2012.

  6. Feldstation FS-5000M, Technisches Handbuch, Teil 1, Beschreibung
    Field Station FS-5000, Technical Manual, Part 1, Description (German).
    March 1994.

  7. Feldstation FS-5000M, Technisches Handbuch, Teil 2, Bedienungsanleiting
    Field Station FS-5000, Technical Manual, Part 2, User Manual (German).
    March 1994.
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Crypto Museum. Created: Friday 20 August 2010. Last changed: Monday, 12 June 2017 - 06:53 CET.
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