HOMEBUILT ACFT HAS RADIO FAILURE; ENTERS CLASS C AIRSPACE WITHOUT CONTACT.

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INCIDENT HAPPENED WHILE ENRTE TO THE OSHKOSH. I DEPARTED MY PVT AIRSTRIP (10 DME ON 278 DEGS RADIAL OFF ESC VOR) WITH MY KITFOX HOMEBUILT AND CALLED UP ZMP AND ASKED FOR VFR FLT FOLLOWING. ZMP CAME RIGHT BACK WITH 'KITFOX STAND BY.' THE FREQ WAS VERY VERY BUSY DUE TO THE AIRSHOW TFC AND I DIDN'T THINK ANYTHING OF IT WHEN THEY DIDN'T GET BACK TO ME. I NEXT TRIED GREEN BAY APCH (GRB) ON 119.4 WHILE STILL 25 MI OUTSIDE THE CLASS C AIRSPACE (ARSA) AND RECEIVED NO REPLY. TRIED REPEATEDLY BUT NO ANSWER. I KNOW THEY HAD AN AVIONICS SHOP ON THE FIELD; WITH THE NEXT ONE BEING IMT; 100 MI AWAY IN THE OPPOSITE DIRECTION; SO I SQUAWKED 7700 FT FOR ONE MIN; THEN 7600 TO LET THEM KNOW I WAS NORDO. THEY SHOT ME A GREEN LIGHT FROM THE TWR WHEN ABOUT 5 MI OUT; SO I CAME ON IN. GREEN BAY HAD ROLLED THEIR 2 CRASH-RESCUE TRUCKS FOR ME AND I FILED A RPT WITH ONE OF THEIR DRIVERS; INDICATING THAT MY ONLY PROB WAS WITH THE RADIO. I HAD ALSO BEEN TRYING TO USE A HANDHELD TRANSCEIVER; BUT COULDN'T REACH THEM WITH IT EITHER! THE AVIONICS SHOP COULD FIND NOTHING WRONG WITH VOLTAGES OR XMIT PWR; ETC.; SO I TOOK THE KITFOX BACK HOME (100 MI AND 2 HRS N) AND GOT OUT THE COMANCHE AND FLEW TO OSH WITHOUT FURTHER INCIDENT. I SHOULD HAVE TURNED AROUND AND GONE BACK HOME WHEN I COULDN'T REACH GRB APCH FROM OUTSIDE CLASS C AIRSPACE; BUT I WAS ANXIOUS TO DISPLAY MY RECENTLY COMPLETED HOMEBUILT AT THE CONVENTION.