Hi, just try this

Updated:

while(<DATA>)
{
=head    
if ($_=~ m#^(\d+)\s+(\w{3}).*?\<\s+((.*?)(mV|db)).*?#gsi)
    {
    print "$2 \t $3\n";    
    }
=cut

if ($_=~ m#^(\d+)\s+(\w{3})(.{24}).*?(\d+\.\d+\s+\w+).*?#gsi)
    {
        #print "$&\n";
    print "$2 \t  $4\n";
    }

}
#output
#abc       450.98 mV
#bcd       50.70  dB
#are       50.00  dB

__DATA__
605 abc xxx        410.00 mV <   450.98 mV     < 490.00 mV
606 bcd yyy        -46.50  dB <   50.70  dB                
607 are zzz                      50.00  dB <   58.48  dB
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