SMA PLT HAS DIFFICULTY WITH APCH DUE TO POOR NDB INDICATION.

Narrative

I WAS BEING VECTORED BY CHARLOTTE APCH FOR THE LOC RWY 2 APCH TO 29J. I RECEIVED MY FINAL TURN AND CLRNC TO INTERCEPT THE LOC AND SHOOT THE APCH; MAINTAINING 2300 FT UNTIL RALLY NDB. I INTERCEPTED THE LOC AND TRACKED IT INBOUND; MY ADF INDICATING RALLY NDB AHEAD. AFTER SCANNING MY FLT INSTS; I GLANCED BACK AT THE ADF WHICH NOW INDICATED HAVING PASSED RALLY NDB; MY FINAL APCH FIX. I NOW BEGAN MY DSCNT AND TIMING FOR MISSED APCH. AFTER HAVING DSNDED FROM 2300 FT TO ABOUT 1400-1500 FT; I WAS INFORMED BY CHARLOTTE APCH THAT I HAD NOT REACHED RALLY NDB AND THAT THEY WERE RECEIVING A LOW ALT ALERT. I IMMEDIATELY BEGAN A CLB AND INFORMED CHARLOTTE THAT I WAS GOING TO CLB BACK TO 2300 FT. CHARLOTTE APCH ASKED IF I WOULD LIKE VECTORS TO SHOOT THE APCH AGAIN WITH THEM CALLING OUT RALLY NDB. I INFORMED THEM THAT MY ADF WAS GIVING FALSE INDICATIONS. THEY GAVE ME VECTORS FOR THE LOC APCH AND CLRNC AND THIS TIME THEY CALLED OUT RALLY NDB FOR ME. THE APCH WAS SUCCESSFUL. HOWEVER; I DID NOTICE ONCE AGAIN THAT THE ADF WOULD APPARENTLY LOSE ITS SIGNAL AND GIVE FALSE INDICATIONS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES THAT MECHS ARE TRYING TO DETERMINE THE PROB. HE HAS THE ACFT IN FOR ITS ANNUAL AND WHEN THAT IS COMPLETED HE WILL TAKE IT TO THE AVIONICS SHOP AND LET US KNOW IF THEY FIND ANY PROBS WITH THE ADF. RPTR CALLED AGAIN AFTER 3 WKS TO SAY THAT THERE IS SOME PROB WITH THE ANNUAL AND HE HAS NOT BEEN ABLE TO HAVE AVIONICS CHK AS YET.