This post is a work in progress. It will be updated over time as I find more relevant information.
What is FT8?
FT8 is a popular form of digital weak signal communication used primarily by amateur radio operators to communicate on amateur radio bands with a majority of traffic occurring on the HF amateur bands.
https://en.wikipedia.org/wiki/FT8
How to use FT8?
To use FT8 you will need a transceiver with the ability to be controlled by your computer. I use my Icom IC-705 connected to a Microsoft Surface Pro by USB to “play” FT8.
Tuning your rig (Icom IC-705) and setup for best results.
What does the signal report mean? How come it can vary so much?
The answer to this can seem a little unexpected, but it appears the answer is that the signal report is mostly influenced by the RF conditions at the receivers QTH. The following explanation was posted on our local email group by Alek VK6APK.
Aha! Good question.
The dB figure is the level above or below your receiver’s noise floor. and is not actually much of an indication of signal strength.
For instance a really popular expedition might be on using FT8 and say you are receiving their signal at 5dB above your noise floor. Then, when they acknowledge you and engage in a QSO, they give you a -20 report. The reason of that is, that you are in a quiet location with not many strong signals filling the spectrum. At the DX end, they have hundreds of people from all over the world, trying to work them. Their bandscope is full and their noise level due to the many signals is very high. Therefore your signal is 20dB below their high noise floor.
If, you were to see VK6DEV’s signal every day, when there were absolutely no other signals on the band, then his signal would be a lot more consistent. That is, every day, you would receive him at close to the same level above or below your noise floor.
Of course, there are many factors other than radio signals which can affect your receiver’s noise floor. Power lines, spurious radiation from electronic devices and power supplies, etc, etc.
To lower the noise floor, the use of things like winding the rf gain control right back, switching in the attenuator, switching off the preamplifier and directional antennas will help a lot. Note that Noise blankers and DSP noise reduction can also lower your noise floor BUT they can also have a very detrimental effect on the decoding of signals, so it is often better not to use them at all.
With a lower noise floor, you will have a much larger dynamic range and you’ll be able to decode lower level signals.
FT8 is a weak signal mode, so the more you can lower your noise floor, the better you will decode signals.
Cheers, Alek.
What constitutes an FT8 contact?
An FT8 Contact is a series of messages passed between 2 amateur radio operators. The six standard messages are:
- CQ <<YOURCALL>> <<YOURLOCATION>> ( CQ VK6DEV OF76)
- <<THEIRCALL> <<YOURCALL>> <<YOURLOCATION>> (M7GBS VK6DEV OF76)
- <<THEIRCALL> <<YOURCALL>> <<SIGNALREPORT>> (M7GBS VK6DEV -03)
- <<THEIRCALL> <<YOURCALL>> R<<SIGNALREPORT>> (M7GBS VK6DEV R-03)
- <<THEIRCALL> <<YOURCALL>> RRR (M7GBS VK6DEV RRR)
- <<THEIRCALL> <<YOURCALL>> 73 (M7GBS VK6DEV 73)
Each call is usually followed by the next in order with the two parties alternating until both have sent a 73.
Variations – Sometimes an operator may use FT8 in turbo mode and short cut some of the messages to speed up a contact.
- In response to a CQ (Call 1) the replying OP may reply with Call 3 instead of Call 2
- In Response Call 4, call 5 may be shortened to (M7GBS VK6DEV R73)
References
Wikipedia – FT8 (https://en.wikipedia.org/wiki/FT8)