A PLT IN A C175 FINDS THAT HIS HEADING CONTINUOUSLY CHANGED AND THE ALERT ARTCC RADAR CTLR DECLARES AN EMER FOR HIM AND VECTORS HIM BACK TO HIS HOME ARPT.

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AT XA30 AM I RECEIVED WX BRIEF PLAN RTE WAS VFR. AT XC30 AM DEPARTED RDD WX DROP TO MVFR SOME PLACES. I RADIOED ZOA FOR FLT FOLLOWING. 20 MINS IN FLT; I REQUESTED IFR CLRNC. AT 5000 FT MSL I ENTER IMC. AFTER ENTERING IMC I RESET THE DIRECTIONAL GYROSCOPE TO COMPASS HEADING; IN THE MEANTIME; I WAS TO CLB TO 11000 FT AT 160 DEG HDG. ATC CALLED AND ASKED ME IF I WAS ON A 160 DEG. I SAID YES. MY DIRECTIONAL GYROSCOPE SAID 160 DEGS; BUT I LOOKED AT MY COMPASS IT SAID 360 DEGS. I RESET AGAIN; AND A FEW MINS LATER; ATC ASKED ME IF I HAD A PROB? I SAID NO. AGAIN ATC ASKED ME TO CHK HEADING. I DID AND MY DIRECTIONAL GYROSCOPE WAS OFF AGAIN. I WAS GOING IN CIRCLES. ATC CALLED AGAIN AND SAID THEY ARE DECLARING AN EMER AND VECTORING ME BACK TO RDD. I WAS IMC AT 10000 FT. I WAS TOLD BY ATC TO DO WHAT SHE SAID AND NOT USE DIRECTIONAL GYROSCOPE OR COMPASS. I WASN'T SURE BY NOW IF THE ALT INDICATOR WAS RIGHT EITHER. SO I USED AIRSPD; TURN BANK AND ALT INFO TO KEEP ME LEVEL. ATC TOLD ME WHEN TO TURN; WHEN TO STOP TURN. ATC GOT ME TO RDD. I BROKE OUT OF IMC AT 2600 FT MSL. AFTER SEEING RWY I CALLED THE TWR FOR REQUEST TO LAND. THEY REPLIED ARPT IS CLR; TAKE ANY RWY YOU WANT. ALSO AT 3500 FT ATC LOST RADIO CONTACT WITH ME. ANOTHER PLT IN THE AIR RELAYED INFO TO ATC. THE ATC CTLR DID A GREAT JOB GETTING ME ON GND. AFTER I WAS ON THE GND; I DISCOVERED THAT I PUT MY HAND-HELD RADIO ON THE DASHBOARD; (MAGNET IN SPEAKERS) BEHIND THE COMPASS. ANYWHERE I POINTED THE PLANE THE COMPASS WENT TO N.