Topband: FT8 Observations

[David Olean]

I have been playing around with FT8 on 160M and am a bit puzzled. I have
made plenty of contacts, but with many stations, it seems to require an
inordinate amount of power to get their attention, or they do not
respond at all. I also have noted that I can hear in a 2.8 kHz passband,
signals that register from -12 to -17 dB. About the weakest that I see
is a bit more than -20 dB. Does this mean that FT8 is only a few dB
better than CW?  I have my time set accurately and I try to place my TX
signal away from whomever I am calling on a clear spot on my waterfall.

Some stations are easy to work, and I have worked across the country
(FN43 to a CM grid) running just 1 watt. It just seems that there are
many stations that are not hearing much, but are making plenty of
noise.  Am I wrong?

I am working on cleaning up my 160 setup and have 8 beverages running
and they are all pretty quiet now that I installed plenty of ferrite
chokes around on the RG-6 feed lines.  I am looking forward to next fall
and winter.

73

Dave K1WHS

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[Tim Shoppa]

On being able to hear signals at -12 to -17 dB on FT8, I do broadly agree. A CW signal at those levels would be easily heard and copied by any decent CW operator.

I think a lot of the FT8 “processing gain” claims, assumes a really poor CW operator. A 0dB FT8 signal is not at noise level, it is way way above noise level.

That said, this morning at my sunrise (noon in Europe) I was printing Italian stations on 40M FT8 and I was being decoded in Europe too, often at the -22 to -24 dB level. (I was barefoot and I’m assuming the italiAns too). Those are levels below what I can hear or copy on CW. I can work Europe midday on 40CW in winter but not so easy in spring or summer.

Tim N3QE

I have been playing around with FT8 on 160M and am a bit puzzled. I have made plenty of contacts, but with many stations, it seems to require an inordinate amount of power to get their attention, or they do not respond at all. I also have noted that I can hear in a 2.8 kHz passband, signals that register from -12 to -17 dB. About the weakest that I see is a bit more than -20 dB. Does this mean that FT8 is only a few dB better than CW? I have my time set accurately and I try to place my TX signal away from whomever I am calling on a clear spot on my waterfall.
Some stations are easy to work, and I have worked across the country (FN43 to a CM grid) running just 1 watt. It just seems that there are many stations that are not hearing much, but are making plenty of noise. Am I wrong?
I am working on cleaning up my 160 setup and have 8 beverages running and they are all pretty quiet now that I installed plenty of ferrite chokes around on the RG-6 feed lines. I am looking forward to next fall and winter.
73
Dave K1WHS
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[Joe Subich, W4TV]

Post by Tim Shoppa
On being able to hear signals at -12 to -17 dB on FT8, I do broadly
agree. A CW signal at those levels would be easily heard and copied
by any decent CW operator.

-12 to -17 dB on FT8 (or any of the other "JT modes") is signal to noise
+ QRM in a 2500 Hz bandwidth. "0 dB" in 'JT speak' is +22 dB S/N for
CW assuming a 100 Hz bandwidth (using the convention of total voltage
from the receiver vs. noise and QRM voltage).

That makes the -17 dB FT8 signal about +5 dB S/N on CW and the mythical
-24 dB (threshold) FT8 signal about - 2dB or -3 dB *below* the copyable
level for a CW signal. JT9 has a threshold of -27 dB ... another 3 dB
more sensitive with its one minute cycle instead of the 15 second cycle
of FT8.

Since the 'JT mode' "threshold" represents a decoding probably of 0.50
(50%) and CW operators, particularly on 160 meters, often operate with
decoding probabilities as little as 10%, one can assume the ultimate
sensitivity for FT8 is 5 to 6 dB better than CW and JT closer to 10 dB
better than CW but it will take some time for experience to prove (or
disprove) those assumptions. The nature of noise, fading and QRM will
also impact the relative sensitivities.

73,

... Joe, W4TV

Post by Tim Shoppa
On being able to hear signals at -12 to -17 dB on FT8, I do broadly agree. A CW signal at those levels would be easily heard and copied by any decent CW operator.
I think a lot of the FT8 “processing gain” claims, assumes a really poor CW operator. A 0dB FT8 signal is not at noise level, it is way way above noise level.
That said, this morning at my sunrise (noon in Europe) I was printing Italian stations on 40M FT8 and I was being decoded in Europe too, often at the -22 to -24 dB level. (I was barefoot and I’m assuming the italiAns too). Those are levels below what I can hear or copy on CW. I can work Europe midday on 40CW in winter but not so easy in spring or summer.
Tim N3QE

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[Mike DeChristopher]

Hi Dave,

In my [very, very, extremely] limited experiences with any of the JT
modes, it has always seemed to me that many are alligators. I think
the FT8 craze has inspired a lot of people to get on 160 with
compromise tx antennas -- this is a good thing -- but I'm not sure
they realize how much they're missing on RX. I'm currently writing an
article for a local club on simple RX antennas for this very reason
(big ft8 crowd). If you try it on other bands, even 80 for example,
you'll find your mileage *magically* improves. The program hears so
well that even a stoopid rx antenna that only slightly pares down the
noise would be fb for most.

As for your tribulations, I don't know enough about the mode to say
too much, but it should be regularly better than CW, even factoring in
the alligators. A local fellow here in WMA probably has 60+ cty on FT8
with only a compromise inverted-L and no RX. I know he's running >10
or 20W -- not sure if that's considered inordinate or not.

Glad to hear your beverage noise is straightened out.

73
Mike N1TA

Post by David Olean
I have been playing around with FT8 on 160M and am a bit puzzled. I have
made plenty of contacts, but with many stations, it seems to require an
inordinate amount of power to get their attention, or they do not respond at
all. I also have noted that I can hear in a 2.8 kHz passband, signals that
register from -12 to -17 dB. About the weakest that I see is a bit more than
-20 dB. Does this mean that FT8 is only a few dB better than CW? I have my
time set accurately and I try to place my TX signal away from whomever I am
calling on a clear spot on my waterfall.
Some stations are easy to work, and I have worked across the country (FN43
to a CM grid) running just 1 watt. It just seems that there are many
stations that are not hearing much, but are making plenty of noise. Am I
wrong?
I am working on cleaning up my 160 setup and have 8 beverages running and
they are all pretty quiet now that I installed plenty of ferrite chokes
around on the RG-6 feed lines. I am looking forward to next fall and
winter.
73
Dave K1WHS
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[Grant Saviers]

Dave,

Remember that the reported S/N is relative to the receive station noise
+ QRM level. Since many TB stations don't have your antennas and have
high noise, they can't decode you or report a poor S/N. I get +9 and
-18 reports from YB stations a hundred KM apart. It's not spotlight
prop. So more power helps. Often I find I need to move TX freq,
especially way into the FT8 band edges when well heard stations don't
decode me, but that is more my experience on 80m long path. The EU QRM
level is clearly a limiting factor. I think the latest release decodes
to -24, I see that sometimes but rarely does the other station respond.
It is always worth calling since their noise level might be a lot lower
than mine. That is clearly the case for some of the skimmer posted
signal reports by great hearing stations that are not on the air. I
will get a -17 report but no other station in that country decodes me
(or decides to answer my CQ DX).

Grant KZ1W

Post by David Olean
I have been playing around with FT8 on 160M and am a bit puzzled. I
have made plenty of contacts, but with many stations, it seems to
require an inordinate amount of power to get their attention, or they
do not respond at all. I also have noted that I can hear in a 2.8 kHz
passband, signals that register from -12 to -17 dB. About the weakest
that I see is a bit more than -20 dB. Does this mean that FT8 is only
a few dB better than CW? I have my time set accurately and I try to
place my TX signal away from whomever I am calling on a clear spot on
my waterfall.
Some stations are easy to work, and I have worked across the country
(FN43 to a CM grid) running just 1 watt. It just seems that there are
many stations that are not hearing much, but are making plenty of
noise. Am I wrong?
I am working on cleaning up my 160 setup and have 8 beverages running
and they are all pretty quiet now that I installed plenty of ferrite
chokes around on the RG-6 feed lines. I am looking forward to next
fall and winter.
73
Dave K1WHS
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[K4SAV]

I'm not sure how many people have actually compared the new digital
modes with CW as far as low signal level decoding. I did that for a
long time when JT-65 first became available. Back then it was much
easier to separate one station and compare the reported S/N to what I
see on my receiver when using a very narrow passband. There was always
a huge disparity, usually 30 to 40 dB. Most of those numbers were taken
right off the main screen of a TS-990s, so the accuracy may not be a lot
but it's a pretty good indication of how close the signal is to the
noise floor.

Then I found this:
http://www.arrl.org/forum/categories/view/31/page:2
You have to sign in to the ARRL site and look for the article titled
"JT65, JT9, FT8, SNR explained".

That article says that the S/N reported by JT-65 is actually 29.7 dB
more than it should be and JT-9 is 31.6 dB more than it should be. That
agrees pretty closely with what I have been observing although my
measurement show a slightly larger difference than that, but that could
be because my measurements didn't have enough accuracy.

I used to try to identify a signal at that was close to the noise floor
and see if JT-9 would decode it. It never did. At a level where JT-9
does decode the signal, it would have been easy copy on CW. So for me,
I see no low level signal advantage to these digital modes. I continue
to wonder why other people say there is. I wonder if others are using a
wide passband when making comparisons (if they really do make
comparisons). For low level CW I usually use 150 Hz, sometimes a little
less if there is QRM.

Jerry, K4SAV
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[David Olean]

  Hi Mike and all who responded.

    I guess I was just underwhelmed at what I could accomplish on FT8
vs CW on 160.  I figured it would open up a whole new level of rare
countries and places that were now workable to me. Working Kazakhstan on
160 CW from my location is difficult, but doable on some nights in the
winter. On FT8 I hear UN1L often, but I can never work him after many
days of trying. I started out with 90 watts and ended up with 900 watts
output, but never a response from him. I guess 160 is a special case
where achieving a good receive noise level is very difficult.  FT8 must
be a huge improvement for those, as you said, with few radials and
smallish vertical radiators as their sole antenna. The extra 5 or 6 dB
must be the difference of night and day for limited space or limited
antennas in general.  It sure has fostered much activity on 160 with
calls that are mostly unfamiliar to me.  I have worked a few regulars on
FT8, like YO3APJ, and they seem to hear just fine. Unfortunately I am
not QRV on other HF bands to try out FT8 there! I suspect the ALLIGATOR
SYNDROME is not as evident on the higher HF bands.

On another subject, I ran out of room on my six position receive
beverage coaxial switch. I had seven beverages, and one was not hooked
up as a result.  I also have not been using diversity reception even
though I am using a K3. So I finally worked out a plan to make a new
switching box. It consists of two Grayhill 12 position rotary switches. 
The two switches have a set of the 12 positions wired in parallel
between the two switches and each position connects to a rx input jack
on the back, while the common terminal for each switch goes to the main
rx jack or the diversity rx jack on the K3.  The 12 inputs are "F"
fittings on the back of the switch box. I worried that the isolation
would be poor, but it checks out at 55 to 65 dB on 160 and 80 meters.
VSWR is pretty good too even with all the insulated wire used. I did not
even try wiring it with coax! One switch selects any of 12 beverage
antennas for the main receiver, while the second switch selects any of
the beverages for the diversity receiver. It works very well and I
wonder why I did not do this a long time ago. In the first evening I saw
a huge improvement using diversity and it was nice having all the wires
available too!  Too bad it won't get much use until next fall and winter!

73

Dave K1WHS

Post by Mike DeChristopher
Hi Dave,
I think it's safe to say that you're running Beverages in a very quiet
location, and the hams that can't hear you are not. What is more, they
might have a 20 over 9 noise level and are running non-directional
antennas (such as verticals with no radials or low dipoles).
73, Mike
www.w0btu.com <http://www.w0btu.com>
I have been playing around with FT8 on 160M and am a bit puzzled. I have
made plenty of contacts, but with many stations, it seems to require an
inordinate amount of power to get their attention, or they do not
respond at all. I also have noted that I can hear in a 2.8 kHz passband,
signals that register from -12 to -17 dB. About the weakest that I see
is a bit more than -20 dB. Does this mean that FT8 is only a few dB
better than CW?  I have my time set accurately and I try to place my TX
signal away from whomever I am calling on a clear spot on my waterfall.
Some stations are easy to work, and I have worked across the country
(FN43 to a CM grid) running just 1 watt. It just seems that there are
many stations that are not hearing much, but are making plenty of
noise.  Am I wrong?
I am working on cleaning up my 160 setup and have 8 beverages running
and they are all pretty quiet now that I installed plenty of ferrite
chokes around on the RG-6 feed lines.  I am looking forward to next fall
and winter.
73
Dave K1WHS
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[Mike Waters]

I have no idea how FT8 compares with other weak-signal digital modes (such
as the ones that JT himself wrote), Dave. If no one knows here, then Google
is your friend. :-)

As for waiting until next fall and winter, keep in mind that we are
approaching the southern hemisphere's fall and winter. Since Topbanders
there have reduced or no lightning QRN, on occasion it's an opportunity for
us to work them!

73, Mike
www.w0btu.com

I guess I was just underwhelmed at what I could accomplish on FT8 vs
CW on 160. ...
... In the first evening I saw a huge improvement using diversity and it
was nice having all the wires available too! Too bad it won't get much use
until next fall and winter!
Hi Dave,
I think it's safe to say that you're running Beverages in a very quiet
location, and the hams that can't hear you are not. What is more, they
might have a 20 over 9 noise level and are running non-directional antennas
(such as verticals with no radials or low dipoles).
73, Mike
www.w0btu.com

Post by David Olean
I have been playing around with FT8 on 160M and am a bit puzzled. I have
made plenty of contacts, but with many stations, it seems to require an
inordinate amount of power to get their attention, or they do not respond
at all. I also have noted that I can hear in a 2.8 kHz passband, signals
that register from -12 to -17 dB. About the weakest that I see is a bit
more than -20 dB. Does this mean that FT8 is only a few dB better than CW?
I have ...

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