FT8 50 Hz Slot Operating Idea.
FT8 by default aligns the TX frequency (audio) to the RX frequency of the station being called. Future transmissions and CQ calls are made on this frequency unless deliberately changed. These will compete with the transmissions of the station just worked. This may result in missed calls due to doubling up of transmissions on the same frequency.
The option of split frequency mode is available but this need to be activated using the "Hold TX Freq" box.
The total bandwidth available for FT8 transmissions for an individual RF frequency is dependent on the receiver bandwidth. This is at least 300 to 2500 Hz but can be higher at 3000 Hz or more depending on the user equipment setting.
Now each FT8 Transmission occupies about 50 Hz bandwidth. Based on the 300 to 2500 Hz bandwidth this gives 44 discrete 50 Hz slots (54 with 300 to 3000 Hz). This is disregarding time slots.
What if each operator operated in the "Hold TX Freq" mode on individual 50 Hz frequency slot (say starting from 300 Hz)? This would mean that some 44 or more operators could transmit at the same time without any frequency transmission conflict. It would be up to each operator to find a suitable 50 Hz slot to suit band activity conditions. With 44 or more slots available this would readily cater for typical 6M DX conditions without the need for doubling up on any 50 Hz slots in most cases.
Any comments?
Igor
VK6ZFG
PS Same concept could also be applies to WSPR with say 10 Hz slots catering for its transmission 6 Hz bandwidth.
Igor
I have racked up some 4000 FT8 QSOs in the last 2 1/2 years - almost all on HF - and I almost exclusively use the "Hold Tx Freq" box ticked. Recently on 50MHz to work some FT8 6M DX, I think everybody whose signals I saw/worked must have had their box ticked. Everyone in VK and ZL just stayed on 'their' one frequency.
Probably 25-50% of HF users seem to leave theirs unticked as they end up, however briefly, on the called station's frequency. The rest (50-75%) stay on a specific frequency regardless of who they work so their box is obviously ticked. It's not rocket science and once ticked, it stays that way until deliberately unticked.
One thing that does become obvious though is that operators do not use the waterfall display effectively. I often see a 'continuous wall of signals" in some parts of the audio spectrum, usually mid-band, from HF while others are sparsely used. The WSJT-X software does a magnificent job of handling overlapping 50Hz signal 'bands', and even one completely of the top of the other. On the subject of the waterfall, remember that what you see denoting activity is not what the people at the other end see. There are so many signals being emitted in Europe and the Americas on HF that don't make it this far around the globe but it makes it hard for us to find a frequency that isn't in use over there. A deliberate operating ploy is to jump your transmit frequency around a bit if you cannot 'make or complete the contact' in the hope that somewhere along the line you will land on a 'clear frequency' at their end. Same thing happens at VHF.
You mention 'at least 300 to 2500 Hz' but I often see signals down at 200Hz and below, and up at 3KHz and slightly over. What some operators fail to recall is that the likes of a typical USB (or LSB) filter attenuates everything below 300Hz and above 2400-2500Hz, not to mention audio filtering in the interconnecting audio interface. Modern DSP rigs have other bandpass options but not all are using these rigs, just luckily I am and I use it carefully. I don't transmit with a setting below 400 or above 2200 as a matter of course.
It comes down to : if you see what looks like a spare 50Hz over several 30 second segments, grab it - but be prepared to QSY as needed.
73 Doug
(16-12-2020, 03:45 PM)VK4ADC Wrote: [ -> ]Igor
I have racked up some 4000 FT8 QSOs in the last 2 1/2 years - almost all on HF - and I almost exclusively use the "Hold Tx Freq" box ticked. Recently on 50MHz to work some FT8 6M DX, I think everybody whose signals I saw/worked must have had their box ticked. Everyone in VK and ZL just stayed on 'their' one frequency.
Probably 25-50% of HF users seem to leave theirs unticked as they end up, however briefly, on the called station's frequency. The rest (50-75%) stay on a specific frequency regardless of who they work so their box is obviously ticked. It's not rocket science and once ticked, it stays that way until deliberately unticked.
One thing that does become obvious though is that operators do not use the waterfall display effectively. I often see a 'continuous wall of signals" in some parts of the audio spectrum, usually mid-band, from HF while others are sparsely used. The WSJT-X software does a magnificent job of handling overlapping 50Hz signal 'bands', and even one completely of the top of the other. On the subject of the waterfall, remember that what you see denoting activity is not what the people at the other end see. There are so many signals being emitted in Europe and the Americas on HF that don't make it this far around the globe but it makes it hard for us to find a frequency that isn't in use over there. A deliberate operating ploy is to jump your transmit frequency around a bit if you cannot 'make or complete the contact' in the hope that somewhere along the line you will land on a 'clear frequency' at their end. Same thing happens at VHF.
You mention 'at least 300 to 2500 Hz' but I often see signals down at 200Hz and below, and up at 3KHz and slightly over. What some operators fail to recall is that the likes of a typical USB (or LSB) filter attenuates everything below 300Hz and above 2400-2500Hz, not to mention audio filtering in the interconnecting audio interface. Modern DSP rigs have other bandpass options but not all are using these rigs, just luckily I am and I use it carefully. I don't transmit with a setting below 400 or above 2200 as a matter of course.
It comes down to : if you see what looks like a spare 50Hz over several 30 second segments, grab it - but be prepared to QSY as needed.
73 Doug
Hi Doug
Your comments are much in line with my thoughts.
The comments are mainly aimed at 6M and for the more limited area of VK & ZL where the number of operators is relatively low.
It was intended to make users that are not aware of the Hold TX Freq option so they can use it to advantage when and if suits them.
On 6M most already use the Hold TX Freq mode but there are some that don't. This is
aimed at these operators and was posted with the other 6M posts for this reason.
With respect to the frequency range operators use I think there is a bit of a conflict here with the more limited SSB audio bandwidth radios and those radios that give you the option of making use of a much greater bandwidth. Obviously using frequencies outside the SSB bandwidth will mean that these are unlikely to be decoded by those restricted to the SSB bandwidth. The use of these "out of band" transmissions is therefore not a good idea. It limits the prospective audience but it some case it could be used for a deliberate reason (eg: used by both operators to get out of the more congested spectrum block).
73s
Igor