NRF51 with PTR5518 range problems

[tanja]

Hi friends,

I'm using a NRF51 IC with this 4.0BLE Modul PTR5518 and i have big problems with Range. As a protocoll i use gazell. In air it is possible do get some correct signals up to 6-7 m but that it don't work properly anymore. If you have a human body in between it is a disaster, you only get good signals with a range <1m. Can i somehow approve this? Please help me if you can. I'm very desperate.

Thank you in advance. Tanja

[Jørn]

Hello tanja

RF systems are very sensitive to their surroundings. Walls that are not in the direct line of sight can reflect the RF signal causing multipath induced attenuation, especially if there is any metal within the walls like pipes or reinforcement bars. Objects in line of sight would typically attenuate or scatter the signal. Other wireless systems operating in the same band can worsen your SNR, and objects close to the antenna will typically alter its characteristics. Testing the range of a system indoors and outdoors can yield very different results.

I would like you to test the gazelle code that comes with SDK 12.3.0 and see how well your system does. I do find it a bit strange that you only get around 7-9 meter range with 4dBm output power and 250kb/s datarate, in my opinion you should have more than that.

I did a quick test with two nRF51 DK's and a slightly modified version of the gzll_ack_payload example. I simply changed it so the host retransmits the button presses made on the device, that way I could see on the device DK that the transmit was successful both ways. I still had a connection around 20 meters away through two glass doors. This office has a lot of metal pipes, some walls of plaster and some of reinforced concrete.

If you have any of our devkits available I would also suggest trying your code on those. This would help eliminate any hardware issues.

EDIT, Additional answers

1. The example is a part of the SDK, you can download it here. The latest SDK version to support the nRF51 series is 12.3.0. The gazell example code can be found in the \examples\proprietary_rf\gzll\gzll_ack_payload subfolder.

2. I think we would need to see the design to properly evaluate it. If you would like for us at Nordic to evaluate your schematic design and/or layout you can either upload it to your original post here on DevZone, or if your design is confidential you can create a mypage case at nordicsemi.com.

3. When frequency hopping the timeslots per channel option affects the number of retransmits before it changes frequency. If many of your channels are filled with noise from other sources this can affect your range. The nRF51's radio has a sensitivity of -96 dBm (0.1% BER) at 250kbps, but if there is a lot of noise present at the receiver you will need a stronger signal, or shorter range, to achieve the same BER.

4. How much power do you measure? Do you have a picture of the measured spectrum?

5. If I completely cover the antenna I have around 10-13 meters range, also through a glass door.

If you still have poor range with the SDK examples there might be a problem with the module you are using.

Best regards

Jørn Frøysa

[Jørn]

I have updated my answer with additional information.