Hi All, 
I have a basic question about network key. Is it  compulsory to have a network key for the receiver, to make connection to a HRM or any ANT device? . We are making  a ANT product by using nRF51422. I tried to connect to a  garmin HRM from sample program of "HRM receiver " given in nRF51422. If i tried to connect with public network key.=0 i always fails to connect but with Network key = { 0x__, 0x__, 0x__, 0x__, 0x__, 0x__, 0x__, 0x__ }. I always succeed . 
please give me some reference . 
thanks 
Robin Singh
[Moderator Edit: Removed ANT+ Network key from public post]