ok i hv to buy antennas from here
plz guide me in that how to select a proper antenna and what should i see when buying one?

1) the one that came with the modules is of approx 6.9 inches and has blue circles on the top end (they say that this is for the frequency blue for 418 and red for 433) ..so should i only match the antenna length when comparing my one with the one im gona buy or should i match the colors too?

2) what about the impedence of the antenna.? how to match it?
(what i think is that just attach a coax cable of 50 ohm to the antenna and then connect the coax to the module)
is is the right approach to match the impedence..?

plz guide me