Still doing FT8 testing this morning 3 hours after sunrise I looked for
something resembling dead band conditions with only a few weak stations.
There was nothing on 160 but the west coast guys were still on 80. They
were weak but there. They would have been good copy on CW but FT8 was
having much difficulty. It was getting only about one decode every 5
minutes or so. Never got a decode of someone sending CQ so that I could
see what FT8 was calculating for a report. This was on my receiving
antenna. I couldn't hear them on the transmit antenna and FT8 never
decoded anything on that antenna.
Based on my tests of mixing noise into the audio and seeing FT8 decode
below the noise floor, I really expected to see better performance from
FT8, but it didn't happen. The dead band test yesterday didn't bode
well for FT8 either.
I think for the test yesterday when mixing in audio noise to cover up
the signals, I had FT8 in deep decode mode. I wonder if those decodes
were just guesses because it knew which stations were on which
frequencies before I added that noise. This deserves a retest.
So I did a retest. This time I set up the noise such that I could just
barely hear the FT8 signals. I did that before I let WSJTX hear the
band, and I set it to decode normally. It didn't do nearly as well.
There weren't many decodes and the signals were being reported in the
range -12 to -17 dB. There were no -24 dB reports like the last test.
where they were all -24 dB I changed the mode to deep decode and let
WSJTX look at the band for a while. Then I added the noise back. Now
there are many more decodes and the reported numbers were much lower.
Hmm. Guesses?
I think I have concluded my FT8 testing. My curiosity of how this works
is sufficiently satisfied. Others can form their opinions from this
data, their own tests, or from whatever source they desire.
Thanks to others that showed some interest in this experiment.
Now that I am feeling better, hope to be up early enough to work some of
that early morning DX that I have been missing and all you other guys
have been getting. (CW of course)
Jerry, K4SAV
On 12/21/2018 5:11 PM, K4SAV wrote:
Yesterday I said " I don't have a measurement with the results of
that showdown of CW versus FT8 in dead band conditions but the answer
would be interesting to know."
This afternoon I tried to get an answer to that. I wanted to see if
FT8 would decode a station I couldn't hear. I wanted to find that
happen and then switch to narrow band CW and see if I could hear him.
I first went to 6 meters but there was nothing there. Then I went to
160 and nothing there. I waited until it was sunset in the northeast.
As soon as that happens the band fills up with stations from that
area. It's not dark here but the S meter immediately goes to S9 plus.
NEWS FLASH for those guys. You can work stations at any time on 160.
You don't have to wait until dark. High power, CW, and a good
receiving antenna is good for about 600-800 miles on 160 at noon. Low
power should also be good but at a little less distance. Don't know
what FT8 will do to the distance.
All those stations were defeating my test to find a condition close to
that of a dead band and a weak signal or two. So I switched to my
receiving antenna and pointed it west to reduce signal amplitudes and
still have some noise.
I can still hear a bunch of signals in there but FT8 isn't decoding
anything with the antenna pointed west. There seems to be some high
level static when pointed west. It's not noticeable on CW but it
sounds bad on USB. Maybe that is causing FT8 to not decode anything.
So I consider this test pretty much unsuccessful. If anyone else runs
a similar test please post the results. I will try again. I know
this isn't a top priority question for most people, but curiosity gets
to me sometimes.
Jerry, K4SAV
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