On 8/9/2023 1:56 PM, Karel Matousek wrote:
I have protest against the use of 1836 kHz frequency for FT4 and FT87
operation.
Your proposal is contrary to the IARU REGION1 HF band plan.
The frequency 1836 kHz is the CW QRP Centre of Activity!
Frequencies between 1838 - 1843 kHz are approved for FT4 and FT8.
https://www.iaru-r1.org/on-the-air/band-plans/
Several thoughts, Karel. First, as long as I've been active on topband,
it has been standard operating practice during CW and SSB contests to
spread over the full width of the band permitted in each operator's
country. During these contests, I regularly hear SSB stations as low in
the band as 1815 kHz and CW stations to well above 1925 kHz. A decade or
so earlier, I heard stations CW stations up to 1950 kHz.
Second, FT8 and FT4 "watering holes" have been in active use on topband
since at least 2014, when I was working EU on JT65 from my QTH near San
Francisco, and during the two seasons of recent solar minimum, I made a
lot of FT8 QSOs to EU. These "watering holes" have been there at least
since 2014 for JT65/JT9, and since 2017 for FT8. FT4 was introduced 3-4
years ago. I very rarely hear FT4 activity on topband, but FT8 is fairly
busy during periods of good propagation. Is it just now that your club
has noticed it to file a complaint?
What I find far more intrusive has been the placement of PSK around 7040
kHz and FT4 around 7048 kHz, when watering holes for other digital modes
on that band have, by long tradition, been above 7070 kHz. More
intrusive because 40M CW and RTTY activity during contests really
starved for spectrum on that band.
All of these frequency choices appear to have been made by developers of
the WSJT software whose primary radio experience was VHF/UHF, who I
suspect have little if any experience with traditional modes on the HF
bands, and, who I suspect, didn't bother to consult with HF operators.
Something else I find disturbing is that those choosing the frequencies
for various digital modes tend to allow far more spacing between their
dial frequencies than needed; an operating window for these modes is
roughly 2.8 kHz, the width of a normal USB signal, beginning 200 Hz
above the dial frequency. There's no good reason a window for another
mode couldn't have a dial frequency 3 or even 4 kHz higher -- FT8
signals are 50 Hz wide, FT4 signals are 83 Hz wide, and both can be
decoded with considerable overlap in frequency, and with one signal
being much stronger than the other. And because both are constant
amplitude frequency-shift modulation with shifts at zero-crossings,
there's little to excite IMD, and the software implements a strategy to
shift the AF during the TX cycle in one direction and the TX dial
frequency in the other so that AF harmonic distortion is killed by the
TX sideband filter! On busy bands, it's not uncommon for 100 signals to
be decoded in a single RX cycle!
Maybe more that you wanted to hear, but things we need to understand so
that the mode is less feared!
73, Jim K9YC
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