Topband: FT-8 performance

Sat Aug 3 19:55:45 EDT 2019

Hello Jerry

When FT8 came out in 2017, I tried it.  Once past the gee whiz factor of the technology, I did not care for it. Being a traditional CW DX chaser on all bands, making FT8 QSO’s did nothing for me. Like kissing your sister.  As the activity picked up on FT8, some soul searching was done.  To continue building Challenge points, it was either adopt FT8 or quit working new ones, primarily on 6 meters, where most of my Challenge opportunity exists.  So, I bit the bullet and moved to FT8, so far only for new ones, and primarily on 6.

FT8 has transformed 6 Meters.  The activity has  nearly all moved to FT8. If you start from scratch today on 6 with CW or SSB only, I don’t know if you could make DXCC in a lifetime.  Will Topband become like this?  I hope not, but don’t know.   The FT8 mode is very effective on 6, QSO’s are in my log which would not be there except for FT8.  Lots of these QSO’s.   Once can argue whether these are QSO’s in the same sense as a CW QSO, but the ARRL says they are, and they are the sponsors/keeper of the awards.  I don’t personally like FT8, but it is a useful tool for making Challenge points.  The needed slots are not available on conventional modes, at least not on 6 meters.

I have spent the entire 6M E skip season in 2018 and 2019 on 6M FT8, and have tried to find meaning in the dB report. Strictly by observation, I can’t correlate the SNR report with an S Meter reading at all.  If my noise level is low, there are several layers of signal audible below S-1 on my IC7610.   It is very common to see a +10 to +15 SNR reading on a sub S-1 signal that does not even move the S meter at all.   I sometimes get lower SNR reports from locals, who do move the S meter to S9 or more.

It seems to have more to do with my baseline powerline noise level, and the number of signals in the passband.  What I do now is pay no attention at all to  the SNR report.  None.  It certainly seems to have no bearing on whether I could make a CW QSO or not with the signal.   Actually, what myself and other experienced CW ops have noticed is we frequently can hear very weak signals on FT8 that do not decode at all.  These would be workable on CW for sure.  However, if the QSB during a transmit cycle drops the signal below the detection threshold for 3 or 4 seconds during a TX cycle, it is not going to decode.   Those are the types of signals which might be workable by good CW ops.  That said, I can frequently decode and work signals that do not meet my hearing threshold.  They just have to hang in for the entire TX cycle and be above the threshold for FT8.

This summer, I ran side by side comparisons with JTDX and FT8 on very weak signals.  This went on for 3 weeks or so, and I became convinced JTDX had superior weak signal decoding and switched to it.  JTDX has multiple decoders and other features which result in more sensitive decodes.  These are predictable.   On a moderately filled band,  WSJTX misses decodes that are -20 or below and JTDX typically gets these.  The decodes are pretty accurate; I don’t get very many garbage decodes.  JTDX was directly responsible for a QSO with 6W1TA which WSJTX missed decoding.

So far, I have worked no new ones on FT8 Topband or 80M, but have listened   With a steady S9 plus 20 to 40 dB roar of NA to NA signals, I am a bit skeptical about how effective it will be contrasted to 6.  However, this year my plan is to pay attention to the low bands on FT8 and see how it works.   I will use JTDX for my testing.

Again, my only interest in FT8 is to work new ones.  I could care less about making hundreds of routine QSO’s on the mode.  Lots of folks do enjoy it, witness the huge amount of activity.

FT8 has been around since mid 2017.  Imagine all the Challenge points, Digital and Mixed DXCC credits that have been awarded.  I don’t see the ARRL backtracking on their initial approach to FT8/FT4 etc.  For myself, I had an attitude adjustment and moved on.

73 Charlie N8RR

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________________________________
From: Topband <topband-bounces at contesting.com> on behalf of K4SAV <RadioXX at charter.net>
Sent: Thursday, August 1, 2019 5:09:55 PM
To: topband at contesting.com <topband at contesting.com>
Subject: Re: Topband: FT-8 performance

I'm not sure how FT-8 calculates the reported S/N number. I found very
little information on the subject and what I did find was not easily
understandable.  What I did was an experiment in which I was able to get
close to the same number being reported.  According to what I have read
about FT-8, it does not implement the same method as I was using in my
testing.

It was very obvious to me that the number being reported was useless.
.Example:  How would you be able to report a S/N of -1 dB when the
station is S9+40 db on the S meter and the receiver reads S1 when tuned
to a spot with no stations.  (Actual measurement)

I made a guess that the number being reported was actually a signal to
noise plus signal ratio S1(S1 + N), where N is the sum of everything
else in the passband.  The S9+40 db station in the example would be the
main contributor to the overall level of the total stuff in the passband
and that total is just a little more than his signal alone, so -1 dB now
makes sense.  This seems to work and it works on other FT-8 signals as well.

Jerry, K4SAV
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