CONFUSION AS TO THE DEFINED CTR OF A TFR WITH A 30 MI RADIUS ENDS IN AN INCURSION INTO THE AIRSPACE EVEN THOUGH THERE WAS CONSTANT CONTACT WITH ATC.

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CALLED FLT SVC STATION AT XA00; WAS TOLD OF TEMPORARY RESTR AREA (TFR). AS I UNDERSTOOD; IT WAS A 30 MI RADIUS FROM THE VENTURA VOR. I TOOK OFF FROM LONG BEACH AT XB30; TURNED W THROUGH THE LA SPECIAL FLT RULES AIRSPACE TO SANTA MONICA; THEN N. I HAD ASSUMED THAT THIS WOULD KEEP ME WELL E OF THE TFR. WHILE TRANSITIONING THROUGH THE SPECIAL FLT RULES AREA I WAS SQUAWKING XXXX AND MONITORING 128.55 AS DIRECTED BY THE LA TERMINAL CHART. AT APPROX 7 MI S OF THE VAN NUYS ARPT; I CALLED SOCAL APCH FOR ADVISORIES TO MY DEST AT MAMMOTH LAKES; CA (MMH). I WAS TOLD TO TURN E TO CLR ME FROM THE TFR AND CALL AN 800 NUMBER AT ZLA. WHAT I THINK I DID WRONG WAS TO ASSUME THAT ALL TFR'S WERE TO BE A FIXED DISTANCE FROM AN ESTABLISHED NAVAID; IE; A VOR. WHEN I HEARD THE FAA WX BRIEFER MENTION A FIX FROM THE VENTURA VOR OF A 037 DEGS AND 5.7 MI; I TOOK THIS TO MEAN THAT THE TFR WAS TO PROTECT SOMETHING FROM THAT LOCATION; NOT THAT THE 30 MI RADIUS WAS TO ORIGINATE FROM THAT POS. THIS OF COURSE EXTENDED THE RESTR AREA MORE EASTERLY THAN I HAD THOUGHT. CONCLUSION; I SHOULD HAVE STOPPED THE FAST TALKING BRIEFER TO ASK SPECIFIC QUESTIONS AND NOT ASSUME ANYTHING. I AM HOWEVER PUZZLED OVER THE FACT THAT I WAS CLRLY SEEN ON RADAR THROUGH THE LA SPECIAL FLT RULES AREA AND MONITORING 128.55. I HAD MADE 3 POS RPTS DURING THIS TIME. COULD ZLA HAVE CALLED TO DIVERT ME? I HAVE HEARD THIS DONE BEFORE! TO KEEP THINGS LESS COMPLICATED; WHY NOT USE A VOR AS THE ORIGIN OF A FIX FOR A SPECIFIC DISTANCE?