Based on an idea received from Ron VK6KDD, here is the description of a cheap TCXO for your TS850 which improves stability a lot, within +/- 4 Hz. It can also be applied to any other rig using a reference crystal.
For about 12 €, you can find a precision crystal heater at Kuhne Electronics by DB6NT. This precision crystal heater provides temperature compensation for crystals, usually found within crystal oscillators. The assembled circuit, which is built on AL2O3 ceramic substrate, should be mounted against the thermostat crystal using heat shrink tubing. The circuit heats the crystal to a temperature of 40.8° C with an accuracy of better than 0.1° C. This provides high frequency stability over the temperature range of -5 to +40° C.
The use at 40°C permits to use standard Xtals, so no need to have a special Xtal. If your rig heats a lot or if you live in very hot countries, this addon will help you only if your rig stays under 40°C working temperature.
Remove the 4 of the 6 screws which give you access to the synthesizer board. Desolder the 20 MHz reference Xtal and heat shrink the heater with a little heat conductive on it.
You can supply the heater with the 9V available on the synthesizer module. Solder a small wire from the left pin (seen from the Xtal) of the 9V regulator to the + supply pin of the heater. Solder another one from - supply to ground. The heater drives about 80mA inrush current, so no worry about this.
For even better performance, you can enclose the TCXO in a polystyrene enclosure. The better the isolation, the better the stability !!
Here a picture of Ron's modification.(Click to enlarge the picture).
Thanks for nice info, Ron VK6KDD !
First published 24/12/2004.