SMA HAS RADIO COM PROB RESULTING IN CLOSE PROX WITH DC9.

Narrative

I WAS FLYING ON AN IFR FLT PLAN FROM PDK TO CRG. WHILE DEPARTING FROM PDK ARPT; I WAS VECTORED TO A POS APPROX 29 NM NE OF THE ATL VORTAC ON APPROX THE 055 DEG RADIAL AT AN ALT OF 4000 FT MSL BY ATL DEP (FREQ 119.3). AT THAT POINT I WAS INSTRUCTED TO CLB AND MAINTAIN 7000 FT AND PROCEED DIRECT MACON WHEN ABLE; WHICH I ACKNOWLEDGED. I WAS RECEIVING THE MACON VORTAC SO I TURNED TO A HDG OF APPROX 155 DEGS AND INITIATED A CLB TO 7000 FT. SHORTLY AFTER THAT; I NOTICED THAT THE ATL DEP FREQ WAS RATHER QUIET AND AFTER A MIN OR 2 I BECAME CONCERNED. I RELAXED WHEN I BEGAN TO HEAR XMISSIONS ON THE FREQ. AT ABOUT THAT SAME TIME; I SPOTTED A DC9 AT MY 9 O'CLOCK POS ABOUT 500 FT ABOVE MY ALT OF 6500 FT. THE DC9 PASSED ME AND THEN TURNED R AND PROCEEDED TO ATL. ATL DEP CALLED ME AND STATED THAT THEY HAD BEEN TRYING TO CONTACT ME FOR AT LEAST A MIN TO GET ME TO LEVEL OFF AT 5000 FT. AT THE CLOSEST POINT I ESTIMATE THAT THE DC9 WAS WITHIN 1 MI OF ME. SHORTLY AFTER THE DC9 PASSED IN FRONT OF ME; I ENCOUNTERED ITS WAKE TURB WHICH I WOULD CHARACTERIZE AS MODERATE. THE REMAINDER OF THE FLT TO JACKSONVILLE WAS ROUTINE. NO PROBS WERE EXPERIENCED WITH THE #1 COM RADIO; WHICH WAS IN USE AT THE TIME OF THE INCIDENT. MOREOVER; NO PROBS LIKE THE ONE EXPERIENCED HAVE BEEN PREVIOUSLY EXPERIENCED WITH THE #1 RADIO. ON THE RETURN TRIP TO PDK; I WAS VECTORED OVER THE SAME GENERAL AREA IN WHICH THE INCIDENT OCCURRED. I NOTED SEVERE STATIC ON THE FREQ (AGAIN 119.3); BUT THERE WAS NO LOSS OF COM. I DISCUSSED THIS SIT WITH A RADIO DESIGN ENGINEER. HE SPECULATED THAT THE NUMEROUS TV AND RADIO XMISSION ANTENNAE IN THE SAME VICINITY THAT THE INCIDENT OCCURRED IN CAN CAUSE INTERMODULATION PRODUCTS WHICH CAN OVERLOAD THE FRONT END OF THE RADIO RECEIVERS. HE SAYS HE HAS EXPERIENCED SIMILAR PROBS IN HIS AIRPLANE IMMEDIATELY S AND SE OF THE PDK ARPT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES THAT HE WAS NOT QUICKLY AWARE OF HIS LOST COM OR HE WOULD HAVE TRIED TO CONTACT ATC. FORTUNATELY THE WAKE TURB WAS NOT SEVERE; BUT HE DID HEAR THAT THE DC9 FLC WAS GOING TO FILE A RPT. THE CTLR DID NOT GET VERY EXCITED WHEN RPTR DID MAKE CONTACT. HIS RADIOS HAVE GIVEN HIM NO PROBS OUTSIDE OF THIS INCIDENT. HE OFTEN HEARS A LOT OF STATIC WHEN FLYING THROUGH THIS AREA BUT NEVER A LOSS OF COM. SEVERAL OF HIS FRIENDS WHO FLY HAVE COMMENTED ON STATIC AS WELL. HIS ENGINEER FRIEND FEELS THERE ARE SO MANY ANTENNAS IN THE AREA THAT IT CREATES INTERMODULATION PROBS WHICH COULD CAUSE THE LOST COM. RPTR DOES NOT FEEL THAT MUCH CAN BE DONE EXCEPT TO MAKE PEOPLE AWARE OF THE PROB TO AVOID A REPEAT OF HIS EXPERIENCE. THE AFFECTED AREA IS 1 MI S OF PDK AND 4-5 MI E OF STONE MOUNTAIN.