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I'm trying to use the cc1200 with the cc1190 range extender on 915MHz. There is no reference design for this combination, so i looked at the most similar one which is the cc1120+cc1190 reference design.
The main issue I still need to sort out is the impedance matching networks + the TX/RX switching. I have problems sourcing components (especially the smd inductors), so I want to redesign the impedance matching networks using component values I already have, and using a microstrip oriented topology to minimize the component count. Is this a good idea or should I just stick to the reference design as-is?
Looking at the reference design, I noticed that the PA output and LNA input of the cc1120 are tied together before being connected to the PA and LNA ports of the cc1190. Since the cc1190 has separate ports for PA input and LNA output, is there a reason why the transmit/receive paths are not kept separate there?
The other issue is that i'm unsure about the specifics of how the TX/RX switching is done in the reference design, both at the cc1120 side and the cc1190 side. The characteristics of the TRX_SW port is not specified in the datasheet (off state impedance and on state impedance), so I'm unsure about how I should connect it to ensure proper switching (there needs to be enough PA to LNA isolation during transmit to prevent damage to the LNA, etc).
I don't have access to a network analyzer at this moment, so I can't measure the TRX_SW port. I'm thinking maybe I should just go with an external switch instead, rather than play tricks with the TRX_SW port like they do in the reference design.
