Maybe it's because
#!/bin/sh
scriptName="bbc_pmt_v5.py -t short -d /dev/dvb/adapter0/demux3"
logName=/dev/null
#logName=/tmp/bbc_pmt.log
while [ 1 ]
do
echo "=== starting $scriptName" >> $logName
$scriptPath/$scriptName >> $logName 2>&1
echo "=== $scriptName exited..." >> $logName
done