PVT PLT OF SMT ACFT INADVERTENTLY PENETRATED AN ARSA.

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I WAS FLYING VFR AT 4500 FT FROM TYR DIRECT AUS. THE BASE OF THE SCATTERED CLOUDS WAS 6500 FT. I HAD NOT RECEIVED A BRIEFING BEFORE LEAVING. LOST TYLER VOR SIGNAL 65 MI OUT. TURNED TO AUSTIN VOR 114.6 AND PROCEEDED ON A 210 HDG. IT IS NORMAL TO HAVE A 20 MIN LAPSE IN SIGNAL BTWN TYLER AND AUSTIN. THE CLOUDS WERE STARTING TO BUILD AND THE CLOUD BASE WAS GETTING LOWER. IT WAS CHANGING FROM SCATTERED TO BROKEN. AUSTIN APCH WAS RECEIVING RPTS OF A CELL BUILDING 15 MI TO THE E AND WAS ASKING FOR ACFT RADAR RPTS. I FOUND IT ON MY RADAR. IT WAS SHOWING UP JUST ON THE CTRLINE AND TO THE R OF MY PATH ON RADAR. VISUALLY IT WAS DIRECTLY IN FRONT OF ME. LISTENED TO ATIS AGAIN; VERIFIED MY NOTES. TRIED 118 ON NAV; NO SUCH FREQ. TURNED TO 117.1. THE NEEDLE SHOWED ME TOO FAR TO THE S TO BE COMING FROM AUSTIN. TRIED TO GET A BEARING FROM GEORGETOWN NDB; NEEDLE WOULD NOT SETTLE. MAYBE I WAS S; TURNED TOWARD VOR SIGNAL. THERE WAS A CITY; AUSTIN; AT 12.6 DME. CHKED TFC AND TURNED L MAINTAINING 4500 TO 4600 FT ALT. SWITCHED TO APCH. I NEEDED TO KNOW IF I WAS CAUSING A PROBLEM AND RPT IF CALL FOR. I FLEW TOWARD A LAKE DIRECTLY AWAY FROM VOR. TUNED TO LEE COUNTY (GIDDINGS) NDB. NEEDLE VERIFIED THE LAKE WAS N OF BASTROP. CIRCLED OVER BASTROP. RPTED MY POS TO AUSTIN APCH; RECEIVED SQUAWK CODE AND PROCEEDED WITH INSTRUCTIONS INTO AUSTIN. SOME OF THE FACTORS CONTRIBUTING TO SITUATION; I HAD NOT RECEIVED A BRIEFING BEFORE LEAVING. TIME LAPSE BTWN VOR SIGNALS HAD BEEN TOO LONG; BUT I KNEW I WAS ON THE PROPER PUBLISHED FREQ AND I WOULD PICK UP ATIS AT 30 MI OUT. I HAD BECOME INVOLVED WITH THE CHANGING WX AND THE EVALUATION OF IT ON THE RADAR. I HAD NEVER ENCOUNTERED A NAV FREQ CHANGE AT AN ARPT. I DID NOT THINK A FREQ CHANGE AT A LARGE ARPT WOULD BE POSSIBLE IN A SHORT ENOUGH TIME NOT TO BE PUBLISHED. I DID NOT UNDERSTAND THE ATIS INFO 'VORTAC IS 117.1 AND CHANNEL 118.' I THOUGHT IT HAD TO BE FOR SPECIAL IFR APCH OR MIL INFO. A FEW MORE WORDS IN THE INFO WOULD HAVE BEEN A LOT CLRER; SUCH AS 'VORTAC FREQ HAS BEEN CHANGED TO 117.1 AND CHANNEL 118.' I KNOW NOW THAT LARGE ARPTS VOR FREQS CAN BE CHANGED WITHOUT PUBLICATION AND HOW TO UNDERSTAND THEM OVER ATIS.