RFX2401C and matching netowrk with nRF24L01+

[Joe Wright]

Hi, apologies for my ignorance but I'm confused by something. I'm looking to add a PA and was thinking of using the RFAxis RFX2401C like many of those nRF24L01+, PA and LNA breakouts are using.

Looking at the RFX2401C, they say it integrates PA, LNA and matching network, but in this white paper hooking up to an nRF24LE1, they still have an external matching networking in the schematic (page 8):

www.rfmw.com/.../RFaxis_Nordic_nRF24LE1_Range_Extension_with_RFaxis RFX2401_App_Note.pdf

Or have I misunderstood what a matching network is?

Thanks, Joe

[bjorn-spockeli]

I understand your confusion and I'll try to explain why the external matching network is needed.

The RFX2401C has internal matching networks on the TXRX and ANT pins to ensure that the input and output impedance are matched to 50 Ohms.

However, allthough the input impedance of the RFX2401C TXRX pin has been matched to 50Ohm, it does not mean that the impedance will still be 50Ohms after connecting it to the nRF24LE1. The ANT lines coming out of the nRF24LE1 must also be matched to 50Ohms before you connect it to the RFX2401C TXRX pin.

The same will apply for the antenna, it must also be matched to 50 Ohms before connecting it to the RFX2401C ANT pin.

-Bjørn

[Joe Wright]

Thanks that's great. With such a PA, can the Johnson 2450BM14A0002 balun be used between it and an nRF24L01+. And if so, is there any advantage?