Antenna matching problem.

I realized a radio module for 433MHz, the chip is nRF9E5, the Nordic recomended application, for 50ohm antenna. Could sm.b. sugest me the simplist method for make the small helical antenna. I have the space for helical antenna D6mm and L<28mm. And how to make antenna adjacement in order to establish the maximal reach .

why dont you use a radio antenna whose length can be varied by pulling it length wise.. for these small RF modules it is useful....

www.pulseelectronics.com/download/3319/w3127pdf

Thank you all, will review the proposals and we will be in touch.