Siretta delta direct connect antennae siretta delta11xsmamss21 the siretta delta 11 is an ism direct connect stubby antenna measuring 902mm in length it is a frac14 wave helically wound omni directional antenna dedicated to 433mhz with a centre frequency of 433mhz this antenna resonates in a far more focused manner than wide band antennas helping it to provide superior performance for short range ism technology 433mhz resides within the industrial scientific and medical ism