locked Re: Performance of FST4-120 vs that of WSPR #FST4 #WSPR


Hi Mike,

FST4W-120 is about 1.4 dB more sensitive than WSPR. I was part of the alpha test team for FST4 and FST4W. Extensive comparisons on 2200 meters under real world conditions showed that FST4W got more decodes than WSPR. FST4 is 1.5 dB less sensitive than FST4W, so that puts it about on par with WSPR. Note that AP decoding offers up to 4.7 dB advantage over FST4 without AP. This means that for messages which can take advantage of AP decoding, FST4 is considerably more sensitive than WSPR.

I am not aware of any controlled, real world comparison of FST4W to WSPR on 630m or 160m. Results there may vary. Please note that these modes were developed for the LF (2200m) and MF (meaning 630m) bands primarily. Achieving the sensitivities noted above requires that frequency drifts and path-induced doppler shifts must be less than the tone spacing over the entire sequence length. These requirements are easily met for the 120 second submodes at LF and MF. Path-induced doppler may be greater at 160m but it is my belief that 120 second FST4 and FST4W submodes should do well there, assuming equipment used has suitably low drift.

Submodes with longer sequence length use narrower tone spacing and thus require greater frequency stability and lower path-induced doppler shifts. Submodes all the way down to 1800 seconds have proven extremely effective at 2200m but the longer 900 and 1800 second variants have been somewhat less so on 630m. This may be due to several factors. Clearly some of the stations trying 300 and 900 second submodes on 630m did not have sufficient transmitter stability. As far as I know, only limited testing of 900 second transmissions has been done on 160m with reasonable success, but I am not aware of testing over paths of great length such as what you are trying to do.

Paul N1BUG

On 2/4/22 18:10, Mike M0AGP wrote:
Hi Jim
It was a sked, having exchanged exact settings including screenshots of settings, etc.
Good that you managed to get a FST4 sked to work, and also with a VK!
I tried with a VK and it failed. A few days later we had freakishly good prop and managed it on FT8 - just barely.
I'm wondering if FST4-120 is actually more sensitive than WSPR in real life situations, not just with white noise testing.
Maybe it is, and I was unlucky in that propagation was always worse when I used FST4.
Mike M0AGP

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