TS-870 modifications
for the DRM receiver


The TS-870 features high-performance circuitry for DSP-based digital processing from the IF stage onwards. The intermediate frequency of the quadruple superheterodyne system are as follows: 1st IF 73.05 Mhz, 2nd IF 8.83 Mhz, 3rd IF 455 Khz and 4th IF 11.3 Khz.

This modification permit to transform the IF output for the SM-230 station monitor (HF 8.83 Mhz) in IF output (BF 11.3 Khz).

It is now possible to connect directly this output to the sound card input of your computer and demodulation numeric radio on short wave. This output is suitable for others applications.

DRM sites:

For use with DRM software tune your receiver on selected frequency and select FM mode. This is due to select width band switch.

Recently I discovered the same modification for the ts-2000:
http://www.arcticpeak.com/radiopages/kenwood_ts-2000_12_khz_if_output.htm

An other solution from Andrea, hb9fbd

I mixed these mods for the TS-870S by inserting a 1microF capacitance in serie with the 1kohm resistor.
The resistor is good to limit the current and the capacitance offer a better circuit separation (in case of shorts!)

The rx result is still very good.

The second things I did is to wire the signal from the IF of 11.3khz to the pin1 (that is nc=not connected) of the ACC2 connector.

The advantage is you do not lose the IF (8.83Mhz) output and you don't need to dismount and disconnectthe board to dissolder the coax.

As for the TS-2000 you can solder the cable to the pin1 of ACC2 directly on the upperside of the board. On pin4 you find a ground to connect the braid of the mini-coaxial cable.

Thanks a lot.

Andrea, hb9fbd


Warning, proceed at your own risk.
If you are not sure don't touch !

Details of modifications

  • Disconnect power supply, antenna cable and any other cables and wires connected to the TS-870.

  • Turn the TS-870 upside down.

  • Remove bottom cover.

  • Disconnect all wires on RF unit (X44-3210-00), dismount plate and unsold coax cable W2 (see Fig. 1)

  • Remount plate and reconnect all wires.

  • At the end of coax cable W2 sold a resistor (1 K). Isolate gnd with tubing.

  • On the TX-RX unit (X57-4620-00) sold resistor to C144 (see Fig. 2)


Fig. 1: W2 coax cable.


Fig. 2: 1 K resistor with tubing


Fig. 3: General vue of modifications.


Fig. 4: Schematic diagram showing the 1 K resistor.