SMA PLT DISORIENTED; MAY HAVE ENTERED RESTR AREA.

Narrative

WHILE ENRTE TO OAK FROM MADERA; ENCOUNTERED DETERIORATING WX CONDITIONS. WAS ABLE TO REMAIN VFR WITHOUT DIFFICULTY; HOWEVER; PRIMARY NAV VOR BEGAN BEHAVING ERRATICALLY WHILE FLYING BTWN LAYERS; AND THEN BECAME COMPLETELY UNRELIABLE. WAS NOT WORRIED BECAUSE WAS ALSO USING A PORTABLE GPS MODEL. ATTEMPTED TO ENTER IDENTIFIER FOR TRACY ARPT (TCY) SO AS TO FLY DIRECT FROM LAST KNOWN POS. THE GPS MODEL DOES NOT HAVE AN ALPHA-NUMERIC KEYPAD TO ENTER DESIRED WAYPOINT IDENTIFIERS; ETC. IT HAS; INSTEAD; ARROW KEYS THAT REQUIRE THE PLT TO SCROLL THROUGH ALL 26 LETTERS OF THE ALPHABET AND THROUGH VARIOUS SYMBOLS AND NUMBERS; AT WHICH POINT THE PLT RELEASES THE UP-DOWN ARROW KEYS ON THE CORRECT LETTER/NUMBER -- A VERY TIME- CONSUMING PROCESS AT BEST (BUT HAS A GREAT ARPT DATA BASE). AS I ATTEMPTED TO GO DIRECT TO TRACY; A FEATURE THAT IS DESIGNED TO BE HELPFUL BY GUESSING WHAT THE LAST LETTER OF THE ARPT YOU ARE ENTERING IS; PREVENTED ME FROM ENTERING THE 'Y' IN (TRACY) 'TCY.' I STRUGGLED WITH THIS COMMUNIST GPS COMPUTER LOGIC FOR A GOOD 5 MINS BEFORE I GAVE UP AND ATTEMPTED TO ENTER NEW JERUSALEM ARPT'S NEARBY NUMERIC ARPT IDENTIFIER. SAME PROB. ANOTHER 5 MINS AT LEAST WASTED INSIDE THE COCKPIT. FOUND A HOLE IN THE DECK; SPIRALED DOWN AND FOUND NEW JERUSALEM ARPT; BUT CANNOT BE SURE I MISSED THE RESTR AIRSPACE AS ALL GND REF WAS OBSCURED. I FEEL THE USER UNFRIENDLINESS OF THE GPS'S LOGIC AND LACK OF AN ALPHA-NUMERIC KEYPAD WAS A MAJOR FACTOR IN THIS INCIDENT.