What is the best Link Budget Nordic engineers have obtained with a nRF51822 Tx?

[Michael]

The device I completed has similar RSSI values at approximately zero distance as my development kit; starting with default Tx of 0dBm from the nRF51822 I achieve approximately -35dBm on my phone that has a generic phone antenna. What is the best Link Budget Nordic engineers have achieved using commerical phones as receivers? What is the best Link Budget Nordic engineers have achieved with custom Tx and Rx modules? In both cases I'm asking about the nRF51822 being used in the Tx module and any break down of where the power is being lost would be appreciated.

[Øyvind Karlsen]

Hi,

The link budget is a measure of how much loss you can have in your channel while still receiving information over it. Your link budget might be 100dBm, which is the best possible scenario for the nRF51, this means that you have +4dBm TX and -96dBm sensitivity (250kbps mode). These 100dBm are then used as a "pool" that you subtract noise factors from, when the pool is empty you are at the maximum range you can have.

Lets say you want to transmit to another chip that is 20m away, lets assume that this equates to 80 dB loss, you also have 5dB loss in your receiver and transmitter chain. This means that out of your link budget of 100dB you now have 10dB left. Lets say that we introduce a wall between the two chips, this wall leads to a loss of 50dB, now we've blown our link budget by 40 dB. In order to compensate we would have to reduce the range, or use amplifiers to increase the transmitted power.

The assumed 5dB loss in receiver and transceiver are something we call matching loss, it is a sum of how well adapted the RF parts of your system are to eachother. For a poorly matched system this can be extremely high, on the order of 50dB, then it is easy to see why a poorly matched system will also have poor range performance.

Best regards,

Øyvind

[Michael]

Thank you for your response. Your last paragraph is what I was interested in. So ideally you are able to get a matching loss as low as 10dB; 5dB from the transmitter and 5dB from the receiver? What is the lowest matching loss engineers at Nordic can achieve?

[Øyvind Karlsen]

For matching losses we see 2dB or less. If you need practical help tuning your device you can get in touch with our support engineers in MyPage.

[Michael]

Thank you for your response, that is very impressive! My first attempt was without any tuning, it seems like I have a lot of work to do.