Kenwood TS-940 measurements and modifications        back to start page

 

Sites of interest for TS-940 owners:

Jeff King (ZL4AI ) collected a lot of valuable information about the TS-940:   http://homepages.ihug.co.nz/~jaking/TS-940_02.htm

Here is a collection of recommended modifications for the TS-940:   http://www.ham.dmz.ro/kenwood/ts-940s-bad-solders.php

More material about the TS-940 is on the mods.dk page (subscription required):   http://www.mods.dk/

More material about the TS-940 (including manuals) is also on the Radio Mods Page of KB2LJJ:   http://kb2ljj.serveftp.com/

 

1. Mods recommended by manufacturer: see service bulletins

2. TS-940 roofing filter

The original roofing filter of the TS-940 has a bandwidth of about 20 kHz, similar as many transceivers of this class. This may cause intermodulation with strong signals on neighboured channels. As expected, my own IP3 measurements showed that the intermodulation distortion falls to relatively poor values when strong signals are within +/- 10 kHz of passband (see diagram).

Inrad offers a 5 kHz crystal roofing filter with 50 Ohm termination impedances and a center frequency of 45.050 kHz (click here). Here is a short report of how this filter can be mounted in the TS-940 (click here).


3. Frontend

Some recent modifications of the TS-940 frontend required intermodulation distortion measurements. The results are summarised in this pdf document.

I have built a prototype of a new frontend. For some photographs of the project click here. I used a Norton preamplifier (2N5109), followed by a H-mode mixer (FST3125) and another Norton amplifier as post-mixer amplifier. A new 2nd mixer for the TS-940 is also under construction.

4. Overvoltage protection 

This document describes a simple crowbar circuit for prevention of damage in case of overvoltace - a known Problem of the TS-940 click here.