PIPER MALIBU MIRAGE ACFT. RPTR PLT CANCELED IFR FLT PLAN AND WAS RECEIVING VFR ADVISORIES WHEN ENTERING CLASS B AIRSPACE AND INADVERTENTLY SWITCHED RADIO FREQ OFF FROM APCH CTLR. TWR CTLR INTERVENED AND TOLD RPTR TO RETURN TO APCH CTLR.

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ORIGINAL FLT PLAN WAS IFR FROM DHT TO SGR AT FL250. ZHU CLRED ME FOR DSCNT TO 13000 FT MSL. AFTER DSNDING BELOW FL180; I CONTACTED CTR; CANCELED IFR AND REQUESTED VFR ADVISORY SVCS WHICH THEY (CTR) GRANTED. NEAR TNV VOR; CTR CANCELED ADVISORIES; INSTRUCTED ME TO SQUAWK 1200 AND TO CONTACT HOU APCH. I CONTACTED HOU APCH ON 123.8 AND WAS GIVEN A SQUAWK CODE. APCH LATER ADVISED RADAR CONTACT AND GRANTED CLRNC INTO HOU CLASS B. I THEN TUNED COM #1 TO SGR'S TWR FREQ FOR MONITORING PURPOSES WHILE MAINTAINING COMS WITH APCH ON COM #2. APPARENTLY; HOWEVER; I ALSO MADE COM #1 THE ACTIVE RADIO; THEREBY CUTTING OFF COMS WITH APCH. AFTER A FEW MINS SGR TWR CONTACTED ME AND ADVISED ME TO CONTACT APCH. AT THAT TIME; I NOTICED THAT I HAD INADVERTENTLY MADE COM #1 THE ACTIVE RADIO. I IMMEDIATELY SWITCHED TO COM #2 AND CONTACTED APCH. THE APCH CTLR WAS VERY TESTY (I CAN UNDERSTAND WHY); TOLD ME I HAD PENETRATED A PARACHUTE AREA AND NOT TO CHANGE FREQS IN THE FUTURE WITHOUT HIS PERMISSION. I APOLOGIZED TO HIM AND STAYED ON HIS FREQ UNTIL ADVISED TO CONTACT SGR TWR. THE REST OF THE FLT WAS CONCLUDED NORMALLY. I HAD A BAD HEADACHE DURING THE LAST 30 MINS OF THIS FLT; WHICH I SUPPOSED KEPT ME FROM THINKING CLRLY; AND I APPARENTLY CHANGED RADIOS WITHOUT THINKING. I SHOULD HAVE NOTICED THAT SOMETHING WAS AWRY DUE TO THE LACK OF RADIO TFC ON A BUSY DAY IN THE APCH AREA. IN THE FUTURE; I WILL BE VERY CAREFUL TO DOUBLECHK MY COM SET-UPS AND TO PAY MORE ATTN TO THE LEVEL OF RADIO TFC.