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.
Comments:
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.
