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← FS-5000
DSU
  
Using the FS-5000 for CW and USB transmission
By Andreas Obermeier

Introduction
The FS-5000 High-Speed-Digital-Data radio set is meanwhile not only popular amoung collectors, it is practically used 'ON AIR' by several radio amateur enthusiasts. Thanks to the first investigations by Brooke Clarke and Ray Robinson (who got the first units without DSU already 14 years ago on the US surplus market...) and Jim Meyer (who supplied information and constantly 'pushed' Ray for more than two years to develop a PIC version of the DSU) we are now able to operate the FS-5000 at least in CW Morse Code mode, even it was never intended for. The only requirement is to have a 'Ray replica' DSU. More information to build your own DSU (based on a PIC) can be found under FS-5000 DCU Replica or go directly to Ray's website.

Thirty years after development and production another goal is to gain more knowledge about this technically very well designed radio set. If you have information please put together as much as possible and make them available to other interested persons and share with them.

Compensate the frequency offset between transmit and receive path
A 'bug' (for amateur radio use only) of the FS-5000 is a system-related frequency offset of 500Hz between the transmitter and the receiver path. First trials to compensate this frequency offset are already realized successful. A clock generator and a small PCB developed by Chris Kunz and Andy Obermeier do the trick. However, this requires additional hardware modification in the modulator part of the transmitter. This modification was designed in a way to easily restore the FS5000 back to its original condition.


In this figure the additional circuit is shown in the upper left corner. To activate this circuit only the existing plug has to be removed and the signal from the PCB has to be plugged in. The original cable can be stored isolated. Power for the small circuit is fed from test point 3 (+5V) near the center of the modulator board. With this modification, the system is now ransmitting with 0 Hz off-set and the narrow CW 300Hz filter of the receiver can be used because the necessary off-set to get a 1000 Hz audio tone is done within the software in the PIC of the 'Ray replica' DSU !

Modifications for transmission of USB voice
The FS-5000 transceiver was designed for upper sideband (Restseitenband Modulation, VSB) digital data transmission by nature. This fact triggered the idea to find a solution to transmit voice additionally. The description of the modulator function and the clear board layout allowed development of such a circuit. This transforms the incoming Voice Audio signal to the required sine and cosine signals.

With these two signals the original modulator is used to generate a voice modulated USB signal. But this circuit is too extensive and can not yet be implemented into the modulator module. For the prototype a case was built that fits exactly the two original battery packs. The idea is to make it smaller just in the size of one battery pack. The necessary connections are made via free pins of the battery connector or wired externally.


Shown here is the FS-5000 with the additional SSB Voice extension box. In a field experiment, CW and USB voice was demonstrated. An additional connector allows connection of a Laptop with sound card or as shown here a NUE-PSK terminal for digital mode operation.

Firmware (V 10.01)
This firmware is in all the SR 5000M Speicher (DSU's) of the complete FS 5000M sets sold by BW Schmitti in April 2012. To get more information how the exact control sequences work the only choice is to take a closer look into the available firmware (V10.01). A portion of the routines to control the radio could be found by Andy Obermeier. Minor adjustments into the firmware allow now to use at least the receiver with the original DSU SR 5000M. The time limitation could be removed. The precise control of the transmitter needs still some interventions. At the moment it is not clear in all points how the transmitter and the antenna-tuner are actually controlled by the original DSU.

Several older versions of firmware must have been available for different users. The known version V10.01 was written on specific customer (Bundeswehr) request. Several facts confirm this speculation:

  • The toggle switches on the receiver were hardwired to prevent accidently wrong settings in the field. To remove this modification, see details Modifying E-5000M for stand-alone use.
  • Not all signals coming from the transceiver are used inside the DSU.
  • Presence of components which were not used by the current firmware e.g. Real Time Clock.
  • Different programming techniques.
  • Existence of program functions that are not mentioned in any description.
  • Parts of unused code still in the chip.
Next steps
The FS 5000 was designed for a very specific purpose. The way to operate it is not as comfortable as for generally known commercial Radio Amateur equipment as it was never intended for. With a few modifications it should be possible (even in a limited way) to be used for common radio amateur modes. Anyway, better than just sitting under glass on a display shelf in the living room. But there is still a lot of work to do:

  • Find a better solution to cancel the frequency offset or alternatively
  • find a way to control the frequency in smaller steps e.g. 100 Hz.
  • Develop an Audio-inverter to add LSB mode.
  • Find and expand the missing features in the original DSU.
  • Improve the operation (Frequency up/down, Memory)
  • ...
Further information
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Crypto Museum. Last changed: Monday, 12 June 2017 - 06:38 CET.
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