nRF52 receive only mode

[Tosa]

Is it possible to put the nRF52 into recieve only mode (say through direct test mode) so that the input impedance can be measured using a VNA? Is the input impedance of the nRF52 exactly 50ohm? We have a short section of PCB (including the pi network pads) from the nRF52 antenna output pin to the antenna. My colleague believes that we need to measure both ways (into the pi-network/antenna and into the nRF52) and use the pi-network to get the complex conjugate of the nRF52's input impedance (which he believes may not be 50ohm). I'm not sure if what he's asking makes sense since if the transmission line is 50ohm, then both antenna and nf52 need to be 50ohm, and even if they are complex conjugates (assuming not 50ohm), they still won't match the 50ohm line...

[FormerMember]

For controlling the radio, I would recommend you to use the radio test example in the SDK.

Yes, both the antenna and the chip should be matched to 50 Ohm.

The nRF52 + C3 and L1 (reference layout) create a 50 Ohm reference point If you follow the reference layout, the capacitor and the inductor form a matching network and harmonics filter, and the output will be 50 Ohm.

Update 11.11.2016: To check the impedance of the chip/chip + matching network for the chip, set the radio in TX or RX and measure the impedance with a network analyzer. The impedance will differ slightly between RX and TX.

[Tosa]

Thanks. I read (after posting the original question) that this blog mentions that C3+l1 at the nRF52 output create this 50ohm termination, and the chip itself is not 50ohm. Hence we would like to look into the the chip (with the termination network of course).

However, I did use this post to originally get the T-network's values which are slightly different (but I suppose I can tune the particular values if my layout doesn't exactly match the nRF52 reference design's).

Edit: looking at the nRF52's reference design files, 3.3nH and 1pF are the actual values for the T-network, which are the same as the nRF51's (but without the extra 1.5pF shunt).

[FormerMember]

I have updated the answer to answer your question.