Ehman has said: "We should have seen it again when we looked for it 50 times. Something suggests it was an Earth-sourced signal that simply got reflected off a piece of space debris." He later took back his some of his doubt, after further research showed a signal coming from Earth to be very unlikely, given that whatever in space the signal would have bounced off of would have had to meet some unrealistic requirements. Also, other problems arise because the 1420 MHz signal is within a a bandwidth reserved for astronomical purposes, in which radios on Earth are banned from using. In a 1997 paper, Ehman suggest that not draw "vast conclusions from half-vast data"— and acknowledged the possibility that the signal may have been military or from people on Earth.