AN INST RATED PLT IN A PA28 IS UNABLE TO ESTABLISH COM WITH PHL TRACON NEAR COL.

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I FLEW IFR FROM BDR TO PNE WITH NO PROBS. ON THE RETURN TRIP I ELECTED TO FLY VFR (VMC ALL DAY). AS I CLBED OUT OF PNE; I CONTACTED PHL APCH FOR FLT FOLLOWING. PHL REPLIED; BUT WAS UNABLE TO XMIT MY RESPONSE. PHL ATTEMPTED TO CONTACT ME SEVERAL TIMES. I HEARD THE CALLS BUT COULDN'T RESPOND (XMIT INOP/RECEIVE OK). I DECIDED TO STAY BELOW PHL CLASS B AND SEE IF I COULD ISOLATE THE PROB. AFTER CLRING PHL CLASS B AIRSPACE I CLBED TO 7500 FT MSL ABOVE NEW YORK CLASS B AIRSPACE; I TRIED SEVERAL METHODS TO CONTACT PHL/NEW YORK APCH CTL AND ZNY. AROUND 5 MI N OF RBV; I SQUAWKED 7600 AND STARTED TO LOOK FOR A PLACE TO LAND; OUTSIDE NEW YORK CLASS B AIRSPACE. I CALLED NEW YORK APCH CTL (EWR) AND GOT ONE RESPONSE; BUT AGAIN COULDN'T ANSWER BACK. I TRIED ONE MORE FREQ (JFK APCH); GOT A RESPONSE; REPLIED AND RESET XPONDER TO 1200. THE REST OF THE FLT WAS OK. I NEVER ENTERED EITHER PHL OR NEW YORK CLASS B AIRSPACE; BUT WAS VERY CONCERNED WHETHER ATC HEARD MY MANY CALLS AND DID NOT REPLY OR DIDN'T HEAR ME AT ALL. I EXPECTED A BROADCAST FROM ATC WHEN I SQUAWKED 7600 TO ASK ME TO IDENT TO VERIFY COM FAILURE. I WASN'T SURE WHETHER I HAD A TOTAL RADIO LOSS.