RADIO COM PROB - GA PLTS WERE EXPERIENCING RADIO DIFFICULTIES DURING THE FLT.

Narrative

DURING OUR FLT FROM DUPAGE TO ST LOUIS; WE WERE EXPERIENCING RADIO PROBS. BOTH RECEIVERS WERE WEAK (SHORT RANGE) AND SCRATCHY. AFTER BECOMING ESTABLISHED ON THE VANDALIA ARR FOR LNDG ON RWY 12R AT ST LOUIS; WE REALIZED THAT THE RADIOS HAD BEEN RATHER QUIET. PRESSING THE 'TEST' BUTTON; WE HEARD APCH CTL CALLING OUR ACFT #. FROM THE TONE IN THE CTLR'S VOICE; IT WAS APPARENT THAT HE HAD BEEN TRYING TO REACH US. WE WERE TOLD TO TURN 20 DEGS L TO REJOIN THE TRANSITION. BOTH OF OUR NAV RADIOS; WHICH HAD A CURRENT VOR CHK AND APPEARED TO BE WORKING PROPERLY; INDICATED WE WERE WITHIN 1 DEG OF COURSE CTRLINE. BECAUSE OF OUR POOR RADIOS AND THE HIGH WORKLOAD; BOTH FOR THE CTLR AND IN THE COCKPIT; WE DID NOT DETERMINE EXACTLY HOW FAR OFF COURSE THE CTLR THOUGHT WE WERE; OR IF HE HAD TO MOVE OTHER TFC TO AVOID A CONFLICT BECAUSE OF OUR TEMPORARY LOSS OF COM. AFTER LNDG; WE HAD AVIONICS CHK THE RADIOS AND IT WAS DETERMINED THAT THE CAUSE OF OUR PROB WAS A POOR GND CONNECTION ON OUR LOWER ROTATING BEACON.