explained in a 1985 interview with Spin
magazine: "All Mexican stations' call letters begin with X. The X stations used to be heard everywhere because of their enormous power. The Mexican government granted licenses with no wattage ceiling. The US, back in the '20s, established 50,000 watts as the maximum. WLS in Chicago is 50,000 watts, and you can hear it like a police call in Houston. I'm sure 500,000 watts you can pick up here in Canada. You can probably pick up XERF. It was just outrageous. You could pick it up everywhere and we'd go. And it would bury everything else. KDRC in Houston was on a close frequency, and they would get stomped on. They had to move. XERF is 1570 on the dial. I think that remains the most powerful station."
Dusty Hill added: "They'll sell segments to anybody. There are a lot of preachers on there. I heard them one time selling autographed prayer cloths. They were to put on your radio when you're listening to these programs. But this one was autographed by Jesus himself. Then you'd hear a 15-minute country western show. Then there'd be a blues show. You could just buy your slot and do whatever. They didn't have a whole lot of restrictions."
Asked if ZZ Top was ever played "on the X," Gibbons said: "We did, in fact. They do not have a pop music playlist, but the song was brought to attention of the station owner, who, it turns out, is an attorney in Del Rio who considers the station his favorite toy. He decided to have a 15-minute pop music segment, and we did get played on XERF and then on XERB in Rosarita. They also have XROC in Juarez. So it went full circle. We heard 'I Heard It in the X' on the X."