Very strong signals on 6688 USB with somewhat weaker signals on 6690 USB, often both going at once causing pretty awful QRM. At one point I think I heard traffic on 6890 LSB as well...making this little chunk of frequency space pretty messy. While this is part of the 6525 kHz to 6765 kHz aeronautical HF band, I have a hard time believing these stations fall within that category. Sounds much more like outbanders on the "45 meter band"