Siretta direct mount antennas siretta delta5axsmamss17 the delta 5a from siretta is a direct connect stubby antenna measuring 100mm in length it is a frac14 wave helically wound omni directional antenna with a centre frequency of 868mhz it is far more focused than wide band antennas such as quad band gsm providing far superior performance this does however mean that the delta 5a is limited to 868mhz only applications 868mhz resides within the industrial scientific and medical