LAUNCHXL-CC1350: What is the correct way to attach an external antenna using the Launchpad CC1350 and the CC-ANTENNA-DK2 kit?

It looks like you have done the connection correctly but it's a bit difficult to see from the picture since it's not in focus.

It looks like you are using antenna #6 which is the same antenna you have on the launchpad. In addition you add a cable with a loss so I would not expect any improvement.

But: You should get better range than a few meters.

First, could you see if you get a difference on 868 MHz? If you use SmartRF Studio and put one board in cont RX (without any known TX on), what RSSI are you seeing on 863 Mhz and 868 MHz? Have you also tried the 50 kbps to see if that make a difference?

Thanks you TER for your fast reply.
Yes the connection seems to be just fine, and im sorry, my smartphone's camera is not good with near objectives.
Yes is the antenna #6. What do you mean with "cable with loss" ?

Experiment 1: Using antenna #6 in 868 MHz
The device without an external antenna is sending the signal
The device with antenna #6 is receiving the signal in mode Continous RX

Distance: 1m
RSSI: -36 dBm at its best and -52 dBm at its worst. It depends on the position of the antenna.
If i choose 863 MHz and repeat this experiment the RSSI just keep its range

Distance: 7m
RSSI: -64 dBm
Frequency: 868 MHz

Distance: 7m
RSSI: -72 dBm
Frequency: 863 MHz

Distance: 15m
RSSI: -95 dBm
Frequency: 868 MHz

Distance: 15m
RSSI: -90 dBm
Frequency: 863 MHz

Experiment 2: Using antenna #6 in 868 MHz Continous RX mode without any device in TX
RSSI: Noise between -119 dBm and -127 dBm

Experiment 3: Using antenna #6 in 863 MHz Continous RX mode without any device in TX
RSSI: Noise between -121 dBm and -127 dBm

Yes, i tried with the 50kbps mode, but i dont see a perceptible difference.

The white cable you use to connect the LP and the external antenna together has a loss of 1 - 2 dB meaning that you get poorer range using the #6 antenna compared to the antenna used on the LP.

How high above ground are your boards when you have done the measurements?

Did you use the same orientation and holding the antenna the same way @7 m and 15 m? The reason I ask is that it looks like the RSSI is better @868 MHz @7 m but the other way around @15 m. The delta should be the same for both distances.

It was an indoor experiment. The altitude from the floor is about 1 meter for emitter and 50cm for reciver. This experiment was produced in the second floor in an appartment from my university.

And yes, i tried to have the same orientation, but of course it was not an in detail experiment, just something fast.

Despite of the altitude and the orientation, i should expect a better transmission performance. What do you recommend to do in this case?

If you have the antenna kit, then it will be better to use antenna nr 9 for your tests. The range will only be degraded using antenna nr 6 since the cable will introduce more losses.
What range do you see if you do not use CC-Antenna-DK2 ? i.e. just between the two CC1350 LPs ?