KENWOOD TS-50 MODIFICATION

DSB Speech Processor

(Speech clipping in the TS-50, published in RSGB's RadCom 1997 June)

INTRODUCTION

For DX work a speech processor should be an advantage but the KENWOOD TS-50 does not have one. The simple speech clipper proposed here does add punch to the signal. It produces more distortion within the pass band than SSB clipping, but if the microphone gain is not set to high this is inaudible; it causes no splatter. 

DESCRIPTION

 Main PCB, TX-RX UNIT X57-4220-11

The clipper (fig») consist of a pair of back-to-back 1N4148 diodes in series with a 10 nF DC-blocking capacitor. It is connected between the collector of Q42 and earth (threaded bushing A1) on the TX-RX UNIT (X57-4220-11). Q42 is the 10.695 MHz double-sideband amplifier between the balanced modulator IC8 and the 2.4 kHz SSB filter. The latter removes intermodulation products of the clipping process outside the normal pass band. This clipper also eliminates the tendency of the TS-50 to splatter when speaking into the microphone too loudly.

INSTALLATION AND ADJUSTMENT

Refer to the manual on page 55:

INSTALLATION

Remove the lid.

Remove the speaker and its mounting plate.

Unscrew and carefully remove the IF filter PCB.

Locate the clipper connection points on the main PCB, near "TH5" and close to L28, and solder, using the threaded bushing A1 as the earth point.

Check the clearance between the clipper components and the filter PCB.

Reassemble.

ADJUSTMENT

In CW mode, send a fast string of dots into a dummy load through an analogue SWR/power indicator and note the average meter deflection.

Swith to menu B nr. 66 "H".

Switch to SSB and speak into the microphone in a normal voice.

Adjust the (yellow) VR7 for an average meter reading just below the one previously noted.