![\"\"\/](\"https:\/\/www.sp3yor.net\/wp-content\/uploads\/2020\/09\/image.png\")
<\/figure>\n\n\n\nTest setup<\/h2>\n\n\n\n
Just so you know – it’s not a laboratory setup, just a quick compare of an old, well-known mode with new and.. better?<\/p>\n\n\n\n
I’ve created the following flowgraph in Gnuradio 3.8:<\/p>\n\n\n\n It can’t be simpler. It plays a .wav file, multiplies all of the samples with some predefined value – lowering the amplitude, then we add some random noise, and the noisy audio goes back out to an actual audio output, monitored by an instance of WSJT-X 2.3.<\/p>\n\n\n\n I’ve also written a simple Linux shell script to take care of running the flowgraph in the right time:<\/p>\n\n\n\n It starts playing the audio a second before period begins, so :59, :14, :29, :44. Convenient for testing.<\/p>\n\n\n\n Let’s start with the new guy first, FST4. I’m playing the recorded message round and round with constant noise level, and gradually increase the signal level by a factor of 0.001. Finally, the message gets decoded with signal level of 0.041.<\/p>\n\n\n\n It’s almost invisible in the waterfall – look at 1000 Hz:<\/p>\n\n\n\n Let’s see how FT8 decoder deals with such a weak transmission. I increase the amplitude to 0.050, then 0.055.. and still no decode. Even though some people would call the signal a booming<\/em> one, by the way it looks:<\/p>\n\n\n\n Only when I reach amplitudes of 0.059 and 0.060, I get some decodes:<\/p>\n\n\n\n I’ve spotted an interesting difference between the built-in decoders: with FST4, WSJT-X gives me the decoded message about 10 seconds into the transmission period – lot of time for me to take some action before the next period. With FT8, decodes appear only during ~14th second. And it’s not that I’m running a Pentium III under the bonnet – it’s a semi decent i7-4702MQ.<\/p>\n\n\n\n The big one? FST4 is better. It’s quicker and it decodes with much weaker signal than FT8.<\/p>\n\n\n\n Obviously it’s just a simulation and it may not translate well to the real life conditions, but in theory, FST4 can decode a message transmitted with 30% less power than FT8 needs.<\/p>\n\n\n\n T Morning update: we’re talking about amplitudes (aka voltages) here, so the difference in dB is 20*log(0.059\/0.041) = ~3.16 dB<\/strong>. ~30% amplitude reduction is equal to a drop in power of a half. That’s even more impressive. A difference between 100W (FT8) and 50W (FST4).<\/p>\n\n\n\n You can check it out on your own – I’ve posted Gnuradio 3.8 flowgraph, wav files (feel free to try your own!) and the terrible runner script in my Github repository: https:\/\/github.com\/olgierd\/ft8_vs_fst4<\/a>. Get WSJT-X 2.3 from https:\/\/physics.princeton.edu\/pulsar\/K1JT\/wsjtx.html<\/a>.<\/p>\n\n\n\n Olgierd SQ3SWF<\/em><\/p>\n","protected":false},"excerpt":{"rendered":" The new beta version of WSJT-X by K1JT gives us access to another new digital mode called FST4. There are some similarities to FT8: it consumes a similar bandwidth, it’s also a single-carrier FSK (GFSK-4, to be exact), transmission period … Czytaj dalej ![\"\"\/](\"https:\/\/www.sp3yor.net\/wp-content\/uploads\/2020\/09\/image-1.png\")
<\/figure>\n\n\n\nwhile [ 1 ]; do if [ date +%S == \"29\" ] || [ date +%S == \"14\" ] || [ date +%S == \"44\" ] || [ date +%S == \"59\" ]; then .\/ft8_vs_fst4.py; break; fi; sleep 0.05; done<\/code><\/p>\n\n\n\nResults<\/h2>\n\n\n\n
![\"\"\/](\"https:\/\/www.sp3yor.net\/wp-content\/uploads\/2020\/09\/image-2.png\")
<\/figure>\n\n\n\n![\"\"\/](\"https:\/\/www.sp3yor.net\/wp-content\/uploads\/2020\/09\/image-3.png\")
<\/figure>\n\n\n\n![\"\"\/](\"https:\/\/www.sp3yor.net\/wp-content\/uploads\/2020\/09\/image-4.png\")
<\/figure>\n\n\n\n![\"\"\/](\"https:\/\/www.sp3yor.net\/wp-content\/uploads\/2020\/09\/image-5.png\")
<\/figure>\n\n\n\nConclusions<\/h2>\n\n\n\n
he difference between 100 W and 70 W is about 1.5 dB. Not much, huh? Still, enough to finish an FT8 QSO, where you missed it by just 0.5 dB \ud83d\ude09<\/s><\/p>\n\n\n\n