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← FS-5000
Modification of the original SR-5000M DSU
By Jim Meyer

When the FS-5000M appeared on the surplus market via BW-Schmitti, they have not been in a condition to be used for Amateur Radio at all... So I guess most of them are collecting dust on a shelf in the living-rooms of collectors !

To use them at least with the DCU made by Ray Robinson (I constructed more then 15 of them in a home-made case same size and appearance as the original DSU SR-5000M), there has to be made the modification already described on these pages, removing the jumper wires at the mini switches at the bottom inside the receiver E-5000M. This modification has to be done first of all.

To use the original DSU SR-5000M, at least to listen to SSB in upper-sideband (USB) or AM broadcast, you need to do a small additional modification that is described in detail below.

The gender changer for the SR-5000M modification

You need to construct a gender-changer from DB25S (socket) to DB25P (plug). Attention, please observe: 25 is GND whilst pin 24 carries the +14,4 Volt Battery voltage ! The gender changer is constructed as follows:

  • Connect the pins 2, 3, 4, 5, 6, 7, 9, 24 and 25 straight through.
  • Solder a 78L05 +5 V regulator to 24 - 25.
  • Route the +5 V from the output of the 78L05 to pin 8 of the DB25P (plug).
  • Solder a 0,1uF capacitor from the +5 V line to GND (between 8 and 25).
  • Do NOT connect pin 8 of the DB25S (socket).

Plug the gender-changer into the socket in the receiver and the DSU SR-5000M into the other side. If the battery is installed or the 220 VAC power is switched on, you will hear noise in the earphone now. Now switch ON the set by pressing both BLUE coloured keys. The switch-on routine will start working and show the self-test. Now do the following:

  • Set a STATIONSNUMMER, e.g. 22.
  • Press the WHITE key.
  • Go to EMPFANG ? and press the WHITE key again to confirm.
  • Enter the EMPFANGSFREQUENZ (five digits with leading zero).
  • The selected digits will be shown instead of the five XXXXX.
  • Push the WHITE key twice and INITIALISIERUNG will be displayed.
  • After approx. 3 seconds this will change to SYNCHRONISIERUNG
  • You will now hear the station on the entered frequency.
  • The bandwidth now is 3000 Hz for SSB in USB or AM broadcast.
After 10 minutes the internal timer circuit of the DSU software is activated and the display is cleared, but reception continues. To change to another frequency press the YELLOW key, followed by the GREEN key, then the WHITE key, then the RED key to clear the frequency.

Now enter the new frequency and press the WHITE key twice. After 3 seconds INITIALISIERUNG it will switch to SYNCHRNISIERUNG and you will hear the station on the new frequency. So at least now one can listen to some stations/traffic and use this very nice and modern radio set.

To switch the set OFF remove the battery from the set or switch the 220 VAC power-line off.

LSB reception
There is no easy way to listen to LSB (Lower Side Band). As the 200 KHz IF mechanical filters have been exclusively produced for the FS-5000M in a mini-version to fit into the DSU SR-5000M there are no LSB filters ever produced in this smaller size. There is not enough space available inside the receiver E-5000M to install the larger normal TFK LSB filter. The only way would be AUDIO FREQUENCY INVERSION with a FX... IC as it has been done already 20 years ago for other commercial surplus radios.

CW reception
Repection of CW (morse) signals is possible by using the 300 Hz filter. This is done by connecting both pins 1 of the DB25 connectors together using a switch.

With this gender-changer I now enjoy the use of the original DSU at least for listening to the bands, even setting the frequency is a little more time-consuming as using the RAY DCU or the miniature "BCD DSU" which is also described elsewhere on this website. Sure one can also open the DSU and go into the "brain, heart and stomache" of the unit to do the changes at the DB25P. If you have any queries do not hesitate to contact me via my web page WWW.QRZ.COM/DB/HS0ZHK.

Helmut "Jimboy" Meyer
9 December 2013

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