C++ Side:

catalog.h:
class Catalog : public QObject
{
...
signals:
    void radioInfoReady(Radio::IssueInfo *issueInfo);
...
}

-------------

QML Side:
...
Connections {
    target: App.Catalog

    onRadioInfoReady: {
        console.log(arguments.length) // 0
        console.log(issueInfo); // undefined
    }
}
...