Hi, I will make another noise from the floor as Iztok wrote as follows,
“Commenting contribution by Take, Igor etc:”
Two topics, hashing and diversity technologies has been repeatedly on the
topics from the readers of this mailing list in the past and are willing to
adopt by the development team by similar reason. On the other hand, I did not
have my memory that “ WSJT-X2.0” and “Dxpedition mode” to be fairly discussed
and adopted among readers of this mailing list. Therefore, I sense there is the
perception gap about the priority of the development task between the
development team and the readers. As I belong to the group the readers, I
naturally have my impression that the development team is hearing Devil’s
whisper too much. I know I am totally wrong but I can not totally deny this
nightmare as I live JA, where a thousand miles away from the development team.
I hope some coordination function will be established to sort out for the
priority list.
Nico, you may discover new diversity merits at HF propagation at Shannon’s
limit region just like you and Steve noticed in M-ary FSK BER vs. Eb/N0 curve
which did not much been addressed in classic textbooks.
Finally, I enjoyed the conversation with you and thank you very much.
73
take
de JA5AEA
Sent from Mail<https://go.microsoft.com/fwlink/?LinkId=550986> for Windows 10
________________________________
From: Nico Palermo <nico...@microtelecom.it>
Sent: Sunday, September 2, 2018 9:19:43 AM
To: k...@arrl.net; WSJT software development
Subject: Re: [wsjt-devel] WSJT-X 2.0 possible new mode/protocol
Most applications of diversity reception are on the MF and low HF bands. I
believe that most fading on these bands is selective fading, where signals
traveling slightly different paths, the low-frequency equivalent of
picket-fencing at VHF/UHF. It might be worth studying propagation on the MF/HF
bands before assuming that the two receivers can be added. I could be wrong,
but I strongly suspect that signals at the two receivers will be displaced in
time, and that the displacement can be a variable by virtue of the variability
of those paths.
Jim,
symbol transmitted by FT8, JT65 and so on are long hundreds milliseconds.
On HFs, such time interval is usually 1) shorter than the channel coherence
time (which is seconds) and 2) still much longer than the channel delay spread
(which is milliseconds).
Therefore, for signals few Hertzs wide, the channel appears as a slow-varying
frequency-flat medium whether you use diversity or you don't.
In these cases space diversity helps only because the probability that two
uncorrelated signals exhibit a given amount of fade at the same time is much
smaller than the probability that a single copy fades out.
Frequency selectivity can be almost safely neglected. You don't need OFDM
systems to cope with selective fading if you are transmitting at few bits per
second in the HFs.
73
Nico / IV3NWV
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