Hi pascal goux

The F3 functionality is explained here in the online SDL Trados Studio documentation:

F3 Concordance Search

It's not possible to set the F3 concordance search to only search the Source. The whole point of both of them being searchable is that when you've already worked on a similar segment that is now saved to the translation memory, you may want to search the source OR the target to find other fuzzy matches, i.e. what has been similar and translated before.

Copying the source segment into the target field means you're treating the source language as if it is the target language. The software cannot recognise that it's a different language and will only search for it in the Target translation units.

it is less time-consuming to click into the Source segment than to change the dropdown menu from Target to Source in the search window.

Alternatively, you could select the following which would leave the Target segment blank until you wanted it to be populated, which can be done via Ctrl+Insert for example.

If you work via 'Translate Single Document', here is where you can prevent the target segment being populated on pre-translation:

If you work with projects, then here is where you make the selection:

I hope this helps,

All the best,

Ali

In addition to the perfect explanation by Alison you might also wish to check the shortcuts for "Source concordance search" (default CTRL+F3) and "Target concordance search" (default CTRL+SHIFT+F3), which work all the time, regardless from where this commands are called.

Thanks Jerzy Czopik 

Thanks Ali and Jerzy, that's very useful.

The "Target concordance search" shortcut is one I forget exists - thanks for jogging my memory!