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Regarding nRF51822 RF Performance

Nazmus Sakib

Hi All.

I am doing a BLE based project using nRF51822. My project is a Proximity Application. Where my device need to talk with an iPhone where I need around 150 Feet (Line of Sight) of Proximity Range. I used in my design nRF58122 QFAA Package and the below RF Parts:

Fractus Chip Antenna FR05-S1-N-0-102: www.fractus.com/.../DS_FR05-S1-N-0-102.pdf

Johanson Balun 2450BM14A0002: www.johansontechnology.com/.../2450bm14a0002-matched-balun-for-nordic-nrf24l01nrf24l01.html

I know Balun BAL-NRF01D3. is the best choice but I am not able to select it due to soldering difficulties.

I found the Chip Antenna FR05-S1-N-0-102 efficiency is good, 72% so I chooses it.

I checked on the nRF Antenna Design guide. Here as I used a ready made Balun so I think there is no other necessary to tune the antenna network as Balun is doing it. Please advise if I am wrong.

I found there are many nRF51822 Modules in Market with long BLE range. Like RFduino Module range I found on web search around 500 Feet (Line of Sight). So I thought my project also can get at least 150 Feet. But unfortunately I am getting only around 3 Feet ...

I used the nRF51822 Internal LDO Schematic Model. I have attached the Schematic and PCB RF trace picture.

Please advise me how to improve the range in such condition to achieve 150 Feet.

Looking forward your suggestion.

Regards.

Schematic_RF.JPG

PCB_RF.JPG

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  • FormerMember
    0 FormerMember

    Hi Nazmus,

    Normally, the range should be better than 5-7m. When using discrete matching network (instead of balun), the layout of the components should be a copy of our reference layout (or as close to a copy as possible). The reason for this is that the placement and the distance between the components influence the impedance.

    Regarding the questions: 1) Yes, the antenna needs an additional pi-network. All the components in the reference layout are for matching the chip to 50 Ohm. And, yes, it is important to tune the antenna.

    2) It is very hard to say what range you can obtain using the Johansson balun. By using the Johansson balun, you don't know to which impedance the chip is matched, so even if the antenna is matched to 50 Ohm, there will still be a mistmatch between the chip and the antenna. It is better to use a discrete matching network, beacuse then both the chip and the antenna can be matched to 50 Ohm.

    Also note that in order to obtain a stable/non-sensitive antenna, the bottom ground layer should be as large and solid as possible, because ground is the reference for the antenna; the impedance of the antenna is 50 Ohm with respect to ground.

    Regards, Kristin

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  • FormerMember
    0 FormerMember

    Hi Nazmus,

    Normally, the range should be better than 5-7m. When using discrete matching network (instead of balun), the layout of the components should be a copy of our reference layout (or as close to a copy as possible). The reason for this is that the placement and the distance between the components influence the impedance.

    Regarding the questions: 1) Yes, the antenna needs an additional pi-network. All the components in the reference layout are for matching the chip to 50 Ohm. And, yes, it is important to tune the antenna.

    2) It is very hard to say what range you can obtain using the Johansson balun. By using the Johansson balun, you don't know to which impedance the chip is matched, so even if the antenna is matched to 50 Ohm, there will still be a mistmatch between the chip and the antenna. It is better to use a discrete matching network, beacuse then both the chip and the antenna can be matched to 50 Ohm.

    Also note that in order to obtain a stable/non-sensitive antenna, the bottom ground layer should be as large and solid as possible, because ground is the reference for the antenna; the impedance of the antenna is 50 Ohm with respect to ground.

    Regards, Kristin

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