Whole house coverage with RF

RE: Whole house coverage with RF

Emil — Fri, 16 Oct 2015 14:25:49 GMT

OK, there seem to be other people asking for a PA circuit approach here: devzone.nordicsemi.com/.../adding-a-pa-to-the-nrf51822

Threre is no visible antenna on the nRF51 as I can see. Is there a hidden trace that is good enough?

An example PA circuit would be very much welcomed!

RE: Whole house coverage with RF

Øyvind Karlsen — Fri, 16 Oct 2015 12:59:39 GMT

For the actual antenna there is not much room for improvement, what you want to improve is the power to the antenna. With the nRF51 you are transmitting around 4dBm to the antenna, you want to transmit somewhere around 30dBm for maximum range while still fulfilling the FCC regulatory specifications. To do this you need to add a power amplifier between the nRF51 chip and the antenna.

RE: Whole house coverage with RF

Emil — Fri, 16 Oct 2015 11:31:01 GMT

Seems like the Gazell is the best option, since the transfer needs to be reliable, although I know you have ACK in the ESB too. I already use the nRF51 DK here with BLE, and I wonder if the 1 pole antenna white paper could be done by attaching a small wire of the same length. The equipment we have now is nRF51 DK, nrf24l01+ with SPI interface (from eBay), and a nRF51822 mini breakout board, with that small zig zag antenna. developer.mbed.org/.../xnrf51822_module.jpg.pagespeed.ic.nbclpwhwGK.jpg

So given these facts, I suppose I should improve the antennae on nRF51 DK right? I know it has a very small RF coaxial output, but should use something else to test?

Thanks!

RE: Whole house coverage with RF

Øyvind Karlsen — Fri, 16 Oct 2015 11:26:18 GMT

For maximum range I would go with either nRF51 or nRF52 series, these have higher sensitivity, which means longer range. The SDK is also more recent (and in my opinion better), which makes development easier. Gazell and ESB are still supported for these newer chips, and you will get better performance in all categories.

The sensitivity of the radio is dependent on how much information you transfer per second, higher sensitivity is achieved by averaging over a larger amount of time to reduce noise. This means that higher sensitivity -> lower transfer rate, which in turn means that higher range means lower data rate. Gazell is essentially a more sophisticated version of ESB, in fact it is built on top of ESB, and has some features like guaranteeing that packets are transmitted, in other words a full link layer.

Best regards,

Øyvind

RE: Whole house coverage with RF

Øyvind Karlsen — Fri, 16 Oct 2015 11:05:15 GMT

The "stubby" antenna is the PCB track that runs next to the coaxial connector. For more information on it please see the quarter-wave printed monopole antenna whitepaper.

RE: Whole house coverage with RF

Emil — Fri, 16 Oct 2015 09:54:29 GMT

Thanks for the fulfilling answer! :) 10-15 m is way too little.

Do you recommend Gazell over ESB / nrf24l01+ for long indoor range applications ? Is there a huge difference between ESB and Gazell implementations code wise? Which one has the most potential range? Also with BLE, I guess I have to pay tons of license fees for the repeater in a mesh network.

RE: Whole house coverage with RF

Øyvind Karlsen — Fri, 16 Oct 2015 09:15:08 GMT

Hi,

If you are going to use BLE, you are limited to a max EIRP of 10mW. The max allowed in the 2.4GHz ISM band is 36dBm or 4W. Range for a radio system is given by Friis transmission equation. For example usage see this thread.

Safe bet on range for BLE is 10-15m, however it depends on what kind of obstacles your signal sees, walls, people, wifi, and more. In order to get good range, your antenna and radio need to be tuned to each other, please see the general PCB design guidelines blog.

If you find that the range offered by BLE is too short, you can add a power amplifier(PA) to your design and use a proprietary protocol, such as gazell. A power amplifier is an additional component that will add cost to your project, there are a lot of commercial products available. Make sure that the PA is matched to the radio at the entry, and also the antenna at the exit, otherwise you will lose performance. A PA typically has some connection points, RF_in, RF_out and some sort of enable mechanism, for the nRF51 you can simply connect the VDD_PA(see product specification) pin which is active when the radio is in TX mode.

Nordic also offers help with RF-tuning of your solution, for more information you can submit a ticket through the MyPage support portal.

Your suggestion of making a mesh style network is also possible, for more information you can have a look at the mesh-network on github.

Hopefully this answers your questions, if anything is unclear, please ask!

Best regards,

Øyvind

RE: Whole house coverage with RF

Emil — Thu, 15 Oct 2015 23:18:58 GMT

So no extra circuitry is necessary. Nice. That answers half my question. Is the stubby antenna the one with a small coaxial connector that fits on the dev board or something?

Thanks again :)

RE: Whole house coverage with RF

Dave_couling — Thu, 15 Oct 2015 23:17:16 GMT

I can only comment on the BLE protocol. The stubby antenna used on the old DK kits are a good example of what antenna to use. I'm not sure amplification is necessary. Though the nRF52 has ~3dB better link budget. So thats something to look into. Front End PA's tend to consume more power then they are worth.

RE: Whole house coverage with RF

Emil — Thu, 15 Oct 2015 23:06:30 GMT

Thanks! Do you have any hints or tips to make such an RF part? The form factor will be small, but it should be possible to just twirl a wire around or something like that. Any idea on how to amplify and attach antenna to NRF51 DK? Also, will pure RF (Enhanced ShockBurst) give longer range with the same power usage?

Thanks!

RE: Whole house coverage with RF

Dave_couling — Thu, 15 Oct 2015 18:46:22 GMT

If you design the RF section well you should be able to cover a house with BLE. Using a stubby antenna, and proper placement should get you pretty close to WiFi coverage from my testing.