Scan efficiency

[pltv]

We have a heavy duty scan based application being built on top of the nRF51822 SOC. We have tested the scan function (S130 SD) on both a custom PCB and also the Nordic Smart Beacon Kit

Very clearly there is a difference in the received signal strength of near by beacons from the same distance (and same positions) with both the Nordic Smart Beacon kit and our custom board. The RSSI values are much higher with the Nordic Smart Beacon Kit compared to the ones shown by the custom PCB.

I am trying to understand better what external factors could influence the RSSI values in a scan function. In both the boards i have a new battery installed and the same firmware loaded. The custom PCB has an external clock so as the Nordic Smart Beacon kit.

Also the advertising packets sent out from the Nordic Beacons seem to have a much longer visibility than the ones sent from the custom board. Again both have the same firmware loaded with same Transmission power settings.

Any inputs on this would be much appreciated

Best Prasanna

[Michael Dietz]

Some things i can think of: The way the antenna was tuned will have a big impact. You would need to test with a network analyzer and optimize the pi tuning network. Also lengths of wires in the high frequency component will have an effect on transmitted power.

If you are using the CSP package these are light sensitivie. if you didnt coat the chip like was done with nordics beacon you will get radio drift which could be your problem.

are you using the latest revision of the nrf51 on your custom pcb? did you solder by hand or have assembled - maybe this could have a small affect on parasitic impedance in the RF part of circuit?

last thing i can think of is maybe the ground/power planes in your pcb design. and did you use the same antenna as the beacon because different antennas will have different specs.

theres a ton of variables when it comes to high frequency design and it could be a lot of things! -Mike

[pltv]

Thanks Mike. At this point we are sourcing the external board from a Chinese manufacturer. We would like to continue to use this board in the short run and may be do a design ourselves after seeing the performance of this board in few pilot tests

Is there a way for us to test and find out the effectiveness of the custom board that we have procured. While the RSSI values could be much lower for our custom board i am interested to know that the sensitivity and effectiveness of the antenna wont drop further after deployment. That will badly affect the application since there is an element of proximity based decision making in the application

[Michael Dietz]

I would assume that the sensitivity and effectiveness of the antenna will change after deployment. You should test the RSSI values while the board is the casing you will use for your product and in a similar environment and see if this is acceptable. RSSI values will change when you incase the board (for example in plastic), based on the environment the device is placed in (reflections caused by walls, refrigerators, etc...). After you do some field testing you can see how much signal strength you have from there and decide if the current boards are sufficient or you will have to invest in improving the RF design of your board.

More complicated tests include hooking up a network analyzer and tweaking the tuning network. You could get an improvement right off the bat if the chip is a WLCSP package and is uncoated (in that case you could coat it yourself)

[Michael Dietz]

infocenter.nordicsemi.com/index.jsp

WLCSP guidelines ^^