DTM queries from sample code in SDK version 16

[jm_laird]

We have a module based on the nRF52840, today we loaded the pre-compiled hex file for the BLE DTM code to 2 nRF52840-based modules and noticed when using the nRF connect DTM program that if one module transmits on channel and the other is set to receive on channel 24, the receiving module is picking up the packets from the transmitter - is this expected behavior? If the mode is changed to sweep, the receiver unit also then starts picking up data on channel 16 from the transmitting device. Why is channel 1 being detected as channel 16 and 24?

Modules are being tested "in air" i.e. not with a conducted cable between them at +8dBm output power with about 5cm separation between the modules

[ketiljo]

When the modules are this close, the field strength will be so high that the receiver may pick up signals on other channels than the wanted channel. 

[jm_laird]

Tried on another board which isn't attached to the other one and you are right, seems to be about 25cm or so of separation is required, thank you.