ATC NAV AID PROB ERRATIC VOR.

Narrative

FOR ABOUT 8 MONTHS I HAVE NOTICED THAT PHOENIX VOR HAS HAD AN ANOMALY IN THE NE QUADRANT. COMING IN ON THE FOSSL 2 ARR; THE COURSE DEV INDICATORS FOR BOTH NAV RECEIVERS HAVE FLUCTUATED PLUS OR MINUS 5 DEGS. THIS OCCURS FROM 30-60 NM OUT AND FROM FL250 AND BELOW. THIS HAS HAPPENED IN DIFFERENT ACFT AND TO BOTH NAV RECEIVERS SO I DON'T THINK IT IS A PROB ON THE AIRPLANES. I KNOW THAT IT HAPPENS IN THE MORNINGS; ALTHOUGH RECENTLY ON AN AFTERNOON ARR; THE VOR SEEMED TO WORK NORMALLY. THIS ANOMALY HAS CAUSED MY ACFT TO START TO TURN IN BEFORE REACHING THE PXR 015 DEGS RADIAL WHEN USING THE AUTOPLT VOR/LOC FEATURE TO CAPTURE THE COURSE. IF IT HADN'T BEEN VFR AND WE WEREN'T FAMILIAR WITH THE GEOGRAPHIC POS OF THE RADIAL WE WOULD HAVE TURNED TO A HEADING OF 195 DEGS ABOUT 8 MI TOO SOON. EVEN IF THE CREW DOESN'T USE THE VOR/LOC FEATURE OF THE AUTOPLT OR FLT DIRECTOR SYS; HAVING THE CDI JUMP INWARD COULD MISLEAD A CREW INTO TURNING IN PRIOR TO THE ACTUAL COURSE. I DON'T KNOW IF THIS ANOMALY HAS CAUSED ANY TFC PROBS. I HAVE MENTIONED IT TO ZAB AND PHOENIX TRACON; AND THEY DON'T SEEM TO HAVE HAD ANY OTHER COMMENTS ABOUT IT. THE INITIAL CDI MOVEMENTS ARE ERRATIC SO MOST PLTS PROBABLY RECOGNIZE THAT THE NEEDLE MOVEMENTS ARE ERRONEOUS. HOWEVER; AS I MENTIONED BEFORE; IF THE CREW USES THE AUTOPLT VOR/LOC FEATURE TO CAPTURE THE PXR 015 DEG RADIAL THE ACFT WILL START TO TURN TO A HDG OF 195 DEGS TOO SOON.