nRF52840 Dongle effective communication range

[Rahav]

I am evaluating the nRF52840 family. The setting for my question is an nRF52840 Dongle and nRF52840 DK, straight out of the box with no configuration changes. Each devices is powered from a different computer USB. The two devices exchange a simple message every 10 seconds, using IPv6 UDP, over a Low-Rate Wireless Area Network (IEEE 802.15.4).

Communication is perfect when the two devices are up to 30 cm away. At 40 cm, it becomes spotty. Beyond that, nearly 100% of the messages are lost. I repeated this measurement with a different dongle with similar results (losing communication at a distance of 90 cm).

I repeated this experiment with two DK and was able to double the range, before communication is lost.

My questions:

Is the effective/expected communication range known? Are the results that I am seeing reasonable?

Is there an antenna for the Dongle or DK that I was suppose to buy?

Are there transmission power settings that I was suppose to configure?

Thanks you in advance for your thoughts.

[ketiljo]

Do you have the dongle plugged into a USB3.0 port? Try using an extension cable to get it away from any USB3.0 devices.

[Rahav]

Thank you for the reply. 

1. Some were plugged directly into USB 3.0 ports. I will buy extension cables and retry. How far do the nRF52840 DK and Dongle need to be away?

2. Are there similar concerns regarding USB 2.0?

[ketiljo]

1. The signal falls of pretty quickly so >10 cm should be ok.

2. Only USB 3.0. Take a look at this: https://www.usb.org/sites/default/files/327216.pdf

[Rahav]

Thank you, your answer was to the point and professional, and a great whitepaper.