Main DXpeditions use a variation of the standard FT8 mode, known as Fox/Hound (F/H in short) or also as FT8 DXpedition mode. In order to make a QSO with those DXpeditions you must make a few changes in your configuration and also observe some basic rules.
You can read the official document explaining this mode, but I find it somehow too complicated for most users, when in fact it is quite simple. Find below a step by step guide to making a QSO with expeditions using this mode.
For 99% of the users, with standard rigs, the best is to disable split operation and leave the program handle it automatically. Go to the "File - Settings" menu option, select the "Radio" tab and then select "None" as Split operation. (Notice: The program recommends and some users say that the "Fake it" option is better, but after my experience and the experience of other OM the option that works perfectly is "None")
Select the "Advanced" tab and there tick the "Special operating activity...." box and select "Hound"
After clicking the "OK" button you will get the following warning message. Don't pay attention to it and simply confirm it.
Monitor the DXpedition frequency and confirm that you are actually receiving the DX station, not only his callers. Notice that Fox/Hound mode should be never run on the standard FT8 frequencies so somehow you should know first the right frequency, for instance from the DXPedition news, from the DX-Spots or tracking their call.
You should receive the DXpedition signal somewhere between 300 and 900 Hz, while the callers should be all above 1000 Hz. In the following example we will try to work the A82Z expedition that is on 18.095 MHz using the FT8 Fox/Hound mode.
When you have confirmed that you receive the signal of the expedition, first look in the waterfall for a clear frequency and select it as your TX frequency (red mark in the waterfall). In this example we will transmit on 1521 Hz. Very important, remember that you must always, without exception, call on frequencies above 1000 Hz.
Then double click on his callsign and the "DX call" box will be automatically filled.
Alternatively you can also type the call in that box and then click the "Generate Std Msgs".
Notice that the Fox (The DX station) is always transmitting in the even (1st) periods, so the "Tx even/1st" box is greyed, because you will be transmitting in the Odd (2nd) periods. This means that your transmission will start in the seconds 15 and 45 of the minute.
Finally click "Enable TX", if not enabled already, to start transmitting and calling the DX station.
The program will automatically keep transmitting, calling the DX station. Depending on propagation conditions and how big the pileup is it can take from a few seconds to many minutes, or even hours, until he replies to you. In order to avoid unattended operations the program will stop the transmission after some minutes of calling unsuccessfully. In that case you have to click "Enable TX" again to resume the transmission.
In this example we can see that A82Z is answering to us, sending a +04 report, and so the program will automatically start sending him a "R+04". Notice that the program has also automatically changed our TX frequency to the frequency of the DX (331 Hz) as this is a part of how Fox/Hound operating mode works.
When the DX receives your R+nn report he will send a RR73 confirming that the QSO is complete and that you are in his log. At this point the contact is finished and you must not transmit anything else (neither 73, nor TNX, etc). In fact the program will automatically disable the transmission.
Finally, If you have configured WSJT-X to do so, it will automatically show the window to log the QSO. Othewise you will have to hit the "Log QSO" button.