Locked Re: Unable to decode FST4W-300 locally on 40m and 30m

Kenji Rikitake JJ1BDX

Alan and all:

I did a quick measurement of an unmodulated carrier frequency drift of FT-891 ("this transmitter"), with the following conditions:

  • FT-891 uses RTTY mode without changing the keying signal (i.e., the output is a continuous carrier)
  • FT-891 output: 5W
  • Output carrier frequency: 10.1355MHz
  • Receiving system for measuring the frequency: Airspy HF+ Dual Port, gqrx 2.11.5, and fldigi-4.1.13 frequency analysis mode
  • Two cases were measured, ~5-minute transmission each, with ~5-minute waiting period

Summary of the result:

  • The 5-minute frequency drift was ~1.5Hz (~0.148ppm), which explains why the transmitted signal of FST4W-300 by this transmitter on the 30m band was not able to decode.
  • First 2-minute frequency drift was ~1.2Hz (in the 2nd transmission case), which explains why WSPR on the 30m band works OK on this transmitter.


  • I've tested FST4W-120 (2 minutes) on 10.1389MHz + 1536Hz with this transmitter and it worked OK.
  • Extrapolating the result into the 80m and the 40m bands suggest that for the 80m band the estimated drift (~0.53Hz) is tolerable but for the 40m the estimated drift (~1.04Hz) is not tolerable, which was consistent with the result of my previous experiment.

The attached files are the PNG file to show the measurement data, the raw measurement data, R command to display the graph.

73 de Kenji Rikitake, JJ1BDX

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