Posted on Feb 6, 2014

The Mainline ST-5 was originally Introduced in the RTTY JOURNAL in May, 1970. It has rapidly become one of the most popular demodulators for RTTY. As back issues have been un available for some time, the original article is being reprinted. For those interested in 100 speed, change the 0. 068 capacitor on the input to the slicer to a 0. 039. A 741 m

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ay be used for the slicer if desired, in which case the 220 pf, 0. 005 Mfd. , and 1. 5K components are left off, as the 741 is internally compensated. Regulated voltage has been added, as shown. Keep in mind also that prices quoted were current at the time the article was originally written. Both Hal Communications and PEMCO, and possibly others, offer boards, components, kits and ready-to-use ST-5 units. Many newcomers to RTTY have complained that a current yet simple de modulator hasn`t been published for them to build. The W2PAT unit in the ARRL handbook is nearly 15 years old. In 1964 an attempt was made to replace the W2PAT design with a modestly priced updated unit, the TT/L-1. This design. together with the subsequent TT/L-2 is now the standard of the serious RTTY enthusiast. However, the original goal was missed by a country mile, since the TT/L-2 costs over $160 just for parts and has l4 tubes. The ST-3 was a successful solid- state design that introduced integrated linear operational amplifiers to RTTY. It was still moderately complex, however, and fell short of the goal to supply the beginner with something that could be built in a few hours. While developing a unit based primarily on ICs to replace the TT/L-2, a very simple modulator with great potential was developed: the ST-5. As with any simple circuit, the cost of the power supply is out of proportion with the rest of the unit. At 1970 prices the ST-5 costs...

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