On 26/07/2017 13:21, Tomas Hood wrote:
Like on SSB, share the spectrum. Take our the defaults in the
software. Let folks figure out a clear area to operate.
HI Tomas,
although I fully understand your concerns and traditional uses of
spectrum should be respected where possible, there are some facts about
FT8 operating that are relevant here. None are any excuse for
transmitting over an existing signal, there's no absolutely substitute
for listening before transmitting and not causing deliberate QRM.
1) FT8 benefits greatly from everyone operating in the same slice of
band, that being what can be heard on a typical USB receiver with an
agreed fixed VFO dial frequency. This benefit is due to being able to
copy almost all signals at once except when transmitting and also
spotting the same decodes to pskreporter and hamspots. Users will
congregate on a common dial frequency whether chosen by usage or by
suggestion from the program authors. The herd effect and its net (both
net and Internet) advantages are certainly part of the success of the
modes supported by WSJT-X.
2) Many users of JT65A on HF will migrate to FT8, mainly because of
potential 4-fold faster QSO times traded off against a few dB less
sensitivity. Having FT8 below JT65A sub-bands where possible will allow
the proportion of bandwidth used by FT8 operators to expand upwards as
JT65A usage drops. This is not guaranteed because usage of both JT65 and
FT8 may increase overall but it does at least set a lower limit.
3) There are a lot of stations active using JT65A and FT8, to give an
idea of this the downloads of the WSJT-X v1.8 beta release that
introduces FT8 are running above 400/day on our secondary release site
(SourceForge, AFAIK I don't think we have statistics for the primary
download site) and over 8000 users are active every day even before any
official general availability release of WSJT-X v1.8. No doubt the
novelty will wear off after a while for some but the trend is up for
now. At times on 20m the suggested 2kHz wide slot from 14.0742 to
14.0762 (14.074 USB dial frequency) is nearly at capacity with up to 40
QSOs concurrently in progress. We are making improvements to the F8
decoder to extract weaker signals, corrupted or truncated signals and
overlapping signals so occupancy is expected to be maybe more than 30
concurrent QSOs per kilohertz, despite the 50Hz bandwidth per signal,
before saturation is reached, maybe more if everyone tries to use the
minimum power required for each QSO.
Here is a snapshot of spots going to pskreporter just now:
Modes over last 2 hours
Mode Count
JT65 70857
FT8 49523
CW 1585
JT9 1459
PSK31 1206
MSK144 487
PSK63 394
SIM31 67
ROS 54
RTTY 47
OPERA 33
SSB 17
16
T10 10
PSK125 5
OLIVIA 3
HELL 2
QRA64 2
FSK441 1
SSTV 1
QPSK31 1
I understand that because WSJT-X and similar applications like JT65-HF
and JTDX do spot all decodes and spots probably reflect actual activity
more accurately than other modes, but the overwhelming numbers show a
picture than cannot be ignored.
4) I have suggested a couple of times that FT8 users operate at the
highest slot available from audio 2150 Hz offset down so as to optimise
overall bandwidth shared by JT65A and FT8 by keeping them squeezed
together. This seems to be working to some extent but obviously it
cannot be easily enforced. Regardless, when there are hundreds of
stations wanting to make QSOs the whole 4kHz (FT8+JT65A) slot will fill
and users will overflow to other bands (a good thing IMHO).
5) The JT9 mode is placed just above JT65A on most HF bands (on some
bands where spectrum space is marginal they share but this really only
works due to lower occupancy overall). JT9 already suffers greatly from
sharing with RTTY stations and is practically unusable on 20m during
international RTTY contests, there is no real problem with that and I
doubt the JT9 signals cause much problem to the often high power RTTY
contesters, but trying to slot FT8 above JT9 will not be practical.
Bottom line is that FT8 is a success and yet it is working for almost
everyone with just 2kHz within the recognized data mode parts of the
band plans. No doubt there is not enough listening (or watching the
waterfall) before transmitting but it is hard to mandate good operating
practice from such a large group probably including many users
completely new to data modes and no doubt to radio in general. Despite
amateur radio operators having vast tracts of spectrum we have to live
both with each other and modes of operation that have different spectrum
needs. I do find it frustrating that there are clearly often more
stations active on FT8, JT65 and JT9 within a 6kHz overall slot than
there are across all the other band users combined in a 350kHz or more
band like 20m, yet the band plans have not caught up with this reality
and rebalanced the proportions accordingly.
I am not offering any clear solution here but hopefully you will
understand that the suggested working frequencies have been discussed
and analysed for the best compromise before being added to the WSJT-X
application. With respect to all the suggested FT8 working frequencies
and the proposed changes on 80m to allow JA operators to join in,
nothing is final, we have not made a full general availability release
of WSJT-X including FT8 yet. If the band planners and coordinators have
better suggestions we will comply. We have done this on 6m in an attempt
to have common international working frequencies despite the region one
data mode allocations being considered as unworkable by many operators
in other regions.
73
Bill
G4WJS.
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