D10 DEP CTLR WORKING 2 DEP POS AND LISTENING ON 2 FREQS HEARS BLOCKED XMISSION; RESPONSE FROM WRONG ACFT; AND MAKES FALSE ASSUMPTIONS.

Narrative

I WAS WORKING DEP 2 AND 3 COMBINED WITH 2 FREQS. ACR X AND ACR Y DEPARTED DFW ON 2 DIFFERENT FREQS. WHILE GIVING A CLB AND TURN INSTRUCTION TO ACR X ON ONE FREQ; ACR Y KEPT READING BACK THE INSTRUCTION ON THE OTHER FREQ. DURING THIS; ACFT Z CHKED ON FREQ CLBING TO 7000 FT. WHEN ACFT Z CHKED ON FREQ; ACR Y WAS READING BACK A CLRNC ON THE OTHER FREQ AND I BELIEVE ACR Y BLOCKED ACFT Z'S XMISSION. I DON'T REMEMBER ACFT Z CALLING ME AND I JUST ROGERED HIM ASSUMING HE WAS ON FREQ AND CLBING TO AT LEAST 8000 FT. I AMENDED ACR W'S ALT TO 7000 FT WITH THE ASSUMPTION THAT ACFT Z WAS CLBING ABOVE 7000 FT. I TURNED ACFT Z TO 270 DEGS AND ACR W TO 260 DEGS. AFTER WORKING OTHER ACFT AND GIVING A BRIEFING TO A DEP 2 CTLR I NOTED THAT ACFT Z WAS LEVEL AT 7000 FT AND I ISSUED ACR W A CLRNC TO MAINTAIN 6000 FT. ACR W WAS AT ABOUT 5700 FT AND WENT TO 6100 FT BEFORE GOING BACK TO 6000 FT. THE 2 ACFT WERE 900 FT APART BUT THEY NEEDED TO BE 1000 FT APART ACCORDING TO THE RULES. THIS ERROR WAS CAUSED BY A POOR ASSUMPTION THAT THE OTHER CTLR CLB TO THE SAME ALT THAT I WAS TRAINED. ANOTHER PROB WITH THIS ERROR IS THAT THE ALT THAT ACFT Z WOULD HAVE BEEN CLBING TO WAS FROM '50 TO 100 THOUSAND FT.' THERE IS NO SET ALT.