[CQ-Contest] FT$ and FT8 Operating Frequencies (was Announcing the half hour NCCC FT4 Sprint Contest this Thursday evening North America time)

[Jim Brown]

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