Greatest Hits has a transmitter on 1107 kHz at Tarbat Ness, which I see is close to Embo. It is probably the first harmonic, which would put it on 2214 kHz. Before RTE closed on 252 kHz, I used to hear a strong harmonic on 504, and a weaker one on 756. Google "DXing Medium Wave Harmonics" for more information on the subject.