UNAUTH RWY ENTRY OP TKOF.

Narrative

AFTER LNDG AT MDW AND DEPLANING MY SON AT THE FBO; I PREPARED TO RETURN HOME (ALTHOUGH THERE HAD BEEN SOME INTERFERENCE VIA HEADPHONES ON APCH; IT HAD NOT SEEMED TO PROHIBIT COM). UPON CHKING ATIS BEFORE STARTUP AT MDW; COM (INFO X-RAY) WAS CLRLY RECEIVED. AFTER STARTUP; COM ATTEMPTS WITH GND RECEIVED CONSIDERABLE INTERFERENCE AS I WAS INSTRUCTED TO TAXI TO 31C. WHEN I REQUESTED CLRNC TO CROSS RWYS 4R/22L; I WAS TOLD BY GND THAT I HAD ALREADY BEEN GIVEN THAT INSTRUCTION; AND I PROCEEDED TO THE 31C RUNUP AREA. THE RADIO HAD INTERMITTENTLY LESS INTERFERENCE WITH MANIPULATIONS. AFTER THE PRE-TKOF RUNUP; I CALLED THE TWR INFORMING THEM THAT I WAS READY FOR DEP. I WAS INFORMED; HOWEVER; THAT I WAS STILL ON GND FREQ; AND I CHANGED TO TWR FREQ; INFORMING TWR; AFTER SEVERAL ATTEMPTS; THAT I WAS READY FOR DEP; AND; ALTHOUGH EXPERIENCING INTERFERENCE; UNDERSTOOD I WAS CLRED FOR TKOF ON 31C AND REPLIED TO TWR THAT I WAS CLRED FOR TKOF ON 31C -- ROGER. I THEN ENTERED 31C ON A TKOF ROLL SEEING NO OTHER TFC. SHORTLY AFTER ROTATION; I HEARD THE TWR ASK IF I HAD HEARD THEM TELL ME TO HOLD SHORT. I REPLIED THAT I HAD NOT HEARD THAT. I WAS ASKED MY DEP HDG AND I REPLIED 240-245 DEGS. TWR THEN INSTRUCTED ME TO CONTINUE VFR AND LATER RELEASED ME FROM RADAR SVC AND TO SQUAWK 1200. UPON RETURNING TO MY HOME BASE; I ASKED FOR UNICOM ADVISORY BUT RECEIVED NO ANSWER AND DID GIVE PATTERN POS AND INTENT. AFTER LNDG; I WAS TOLD THAT; ALTHOUGH I WAS RECOGNIZED; MY XMISSION WAS GARBLED AND AN ADVISORY HAD BEEN GIVEN TO ME. IT WAS SUGGESTED I ATTEMPT TO XMIT AFTER SHUTDOWN. THIS PROC REVEALED THAT WE WERE ABLE TO COMMUNICATE WITH LITTLE STATIC. IT ALSO REVEALED THAT THE VOLUME KNOB WAS SO LOOSE THAT ONLY A COUPLE OF MILLIMETERS WOULD SHUT OFF THE VOLUME. THE ENG HAD BEEN RUNNING ROUGH ON THE TRIP; (MAGNETOS; CARB HT; AND FUEL CONTAMINATION HAD ALL CHKED PROPERLY). THE FBO RECOMMENDED CHKING THE SPARK PLUGS AND LEADS. SPARK PLUGS HAVE BEEN PURCHASED FOR INSTALLATION AND LEADS WILL BE CHKED AS WILL THE REPAIR OF THE VOLUME KNOB. BETTER RADIO MAINT SHOULD HAVE PREVENTED RADIO PROBS. MORE REST AND LESS ANXIETY COULD HAVE ALERTED THE PLT TO PROBS EARLIER.