g_chann = '';
if(google_ad_channel != null && typeof google_ad_channel != 'undefined') {
    g_chann = google_ad_channel;
}
else if(google_afs_channel != null && typeof google_afs_channel != 'undefined') {
    g_chann = google_afs_channel;
}
else {
    g_chann = '';
}