C210 PLT HAD AN ATC COM FAILURE WITH ATC WHILE BEING VECTORED TOWARD HIGH TERRAIN IN SCT CLASS B.

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FLYING IFR IN VFR CONDITIONS FROM ELP TO VNY; THE WX AT VNY WAS 2000 FT OVCST AT +/- 4000 FT TOPS. SO CAL APCH HANDED ME OFF TO SO CAL SE OF BURBANK AND WE WERE DIRECTED ON HDG 020 DEG AT 6000 FT. ABOUT WHITEMAN ARPT ; NO MORE DIRECTIONS FROM ATC WERE HEARD. ONE OTHER ACFT WAS HAVING A DIFFICULT TIME TALKING TO ATC AND I HEARD NO ATC RESPONSE. SINCE WE WERE VFR ABOVE THE TOPS AND THE ACTION AREA WAS VFR; I NOTICED WE WERE APCHING THE N MOUNTAINS N OF OUR NORMAL VECTORING TO THE VAN NUYS LOC. I INFORMED ATC THAT I WAS EXECUTING A L TURN TO JOIN THE LOC. NO RESPONSE. AFTER THE THIRD TIME I THEN HEARD A SCRATCHY; THEN A GOOD XMISSION FROM SO CAL. THEY HAD BEEN TRYING TO REACH ME 5 TIMES TO NO AVAIL. I CONSISTENTLY HEARD OTHER ACFT. EITHER THERE IS A DEAD ZONE WHERE WE CANNOT RECEIVE SO CAL (120.4) OR THEIR TRANSMITTER FAILED. HAD WE BEEN IMC AND A PLT NOT CHKING OUR LOCATION; WE WOULD HAVE BORED INTO THE MOUNTAINS. THE CTLR SOUNDED SLIGHTLY SHAKEN WHEN HE WAS FINALLY ABLE TO XMIT TO ME. I HAVE NOTICED ON THE LYNXX ARR THAT 120.4 DOES NOT GET TO US UNTIL WE ARE VERY NEAR THE LOC.