Leif and all --
It has been some time since your email of October 18, but I have finally
found time to think about some of the suggestions you made for
optimizing Linrad parameters for use with WSJT/JT65.
You suggest using fft1 BW=80 Hz, sin^3 window, first mixer BW reduction
parameter=3, a large storage time (perhaps 15 s ?) for fft2, and a large
averaging number (say 100) for the hi-res graph. OK, these are close to
the parameters I have been happily using.
Then you say
With these parameters Linrad is very sensitive in the main waterfall
provided that the waterfall is made very slow. No more than
10 lines per second. The reason is that S/N may be lost in the process
of converting the 16384 spectrum to a waterfall of about 100 pixels.
I do not understand these sentences at all. Did you possibly mean "no
more than 0.1 lines per second" and "a waterfall of about 1000 pixels"
?? (You are speaking of the wide-graph waterfall here, not the baseband
waterfall -- right?)
You repeat the "10 lines per second" comment later in the same
paragraph. I cannot imagine why one would want to run the waterfall at
such a high speed for JT65, so I suppose this was just an unintended
mistake?
I also do not understand your brief calculation suggesting that the main
waterfall (meaning the wide graph, right?) should reveal signals down to
-35 dB on the WSJT scale. It's true that in practice I have lots of
birdies (though not "thousands" of them, I believe); but as I have it
set up I can see JT65 signals only down to perhaps -24 dB on the wide
waterfall. The WSJT ("SpecJT") waterfall makes it possible to see JT65
signals down to around -29 dB, or about the limit of the DS decoder.
The SpecJT waterfall uses 2.7 Hz per pixel, N=4096 FFTs with no
windowing, and I generally run it at its slowest rate, about one line
every 3 seconds. I do not see how it could be possible for the Linrad
wide-graph waterfall to achieve sensitivity as good as this one does,
while displaying anything like 90 kHz of spectrum. What have I missed
in understanding what you wrote?
-- Joe, K1JT
#############################################################
This message is sent to you because you are subscribed to
the mailing list <linrad@antennspecialisten.se>.
To unsubscribe, E-mail to: <[EMAIL PROTECTED]>
To switch to the DIGEST mode, E-mail to <[EMAIL PROTECTED]>
To switch to the INDEX mode, E-mail to <[EMAIL PROTECTED]>
Send administrative queries to <[EMAIL PROTECTED]>
