What was found
AIRCRAFT WAS GROUNDED: UPON DEPARTURE, AIRCRAFT LATERAL NAVIGATION WOULD NOT ENGAGE. LOST FLIGHT DIRECTORS AFTER ATTEMPTING TO ENGAGE HEADING MODE. AUTOPILOT AND AUTO THROTTLE WOULD NOT ENGAGE. GEAR HORN WOULD NOT EXTINGUISH. PWS LIGHT ILLUMINATED AT THE SAME TIME. DECESION MADE TO RETUN TO STL. NO EMERHENCY DECLARED AND LANDED WITHOUT INCIDENT. MAINTENANCE T/S FOUND RADIO ALT DISAGREE. FOUND #2 R/A RCV ANTENNA RESISTANCE HIGH. REPLACED ALL 4 ANTENNAS PRECAUTIONARY. IAW AMM 34-33-11.