Improving range of nRF24L01+

Hi,
I know there is such topic again and again but despite a lot of Googling I did not came to some conclusion so I ask for help. My setup is:
Battery powered transmitter outside - average consumption is < 10uA and I would like to keep this.
Something like 10-20 m distance with one wall and some bushes in line of sight.
Receiver with “unlimited” power inside.

Currently I am using the cheapest PCB antenna nRF modules for the communication (eBay fakes ofc). The range is “marginal” - for fixed RX location it is possible to find a location where the signal is good. But when RX is moved signal is lost. For improving the range I currently did:
I soldered 10uF ceramic caps directly to power pins of the module and I have a 1000uF electrolyte cap nearby.
While transmitting both RX and TX ATMega is in deep sleep with only timing crystal running to reduce switching noise. No other digital IC is present.
I have implemented a protocol which tries to find a frequency where communication is possible.

Other possible improvements I consider are:

  1. Reducing message length - currently I have 4 bytes of address, 5 bytes of payload and 2 bytes of CRC. Do you think reducing the address to 3 bytes and CRC to 1 byte and splitting the payload would increase the range considerably or it will only increase error rate?
  2. Modify the antenna - some people claim soldering wire to the antenna (or replace it) increases range. But other say it only introduces mismatch between antenna and nRF drivers possibly overloading and damaging the chip. Also since I don’t understand RF I don’t know how to do it.
  3. Add shielding to the module - but again I don’t know how to do it and why it should increase range.
  4. Use directivity of the antenna. AFAIK it is difficult to make an omnidirectional antenna and so the PCB antenna is likely to have directions where the signal is better then in other. Are there such directions? I guess the PCB antenna is designed to be as much omnidirectional as possible so probably not? I tried rotating the module and did not notice a difference - moving it was much more important than direction.
  5. Using better hardware. I have already ordered a PA+LNA module for RX but I think I cannot use it for TX because it consumes much more power. But I have found it is possible to get a nRF module with connector for external antenna but without PA+LNA. Would such module increase range without too large increase in current consumption?

EDIT:
There are pictures of my TX, maybe someone will see some stupid layout mistake reducing the range greatly.


Side.jpg

Top.jpg

The way your antenna is mounted it is being shielded by the Atmega chip and the PCB. When I built a similar unit I mounted the nRF24 well clear of the PCB and at right angles to it. It is to the right of the red arrow in the photo (otherwise ignore the arrow :slight_smile: )

ModelTrainDSCF4238partA.png

…R

Smajdalf: 2) But other say it only introduces mismatch between antenna and nRF drivers possibly overloading and damaging the chip.

Indeed they do, and a better option is to get a high power NRF with the antenna supplied. They are twice the price but still cheap, and you only need one. I believe Stanley Sieow in KL gets about a kilometer.

Robin2: The way your antenna is mounted it is being shielded by the Atmega chip and the PCB. When I built a similar unit I mounted the nRF24 well clear of the PCB and at right angles to it. It is to the right of the red arrow in the photo (otherwise ignore the arrow :) )

As I said I know very little about RF. Do you think it is important and worth redesigning the board? I admit I tried to make the board small and SPI lines short and only when it was finished I realized the layout may be poor. I noticed you know a lot about nRFs - maybe you did some experiments how better layout improve range or I need to do it myself? I think one advantage of nRF with external antenna would be fix of the layout problem. BTW everyone says external antenna is better than the PCB one. Why? Is it more directional, does it consume (and radiate) more power or is it more effective radiating more power with the same power consumed?

Here is a link to a modification of the pcb antenna to replace it with a dipole antenna. I’m not sure if it fits with your layout, but the performance is claimed to be in between the standard module and the PA-LNA models. The project seems to be pretty well documented.

If you can get the external connector on the standard module, its worth a try.

Smajdalf: As I said I know very little about RF. Do you think it is important and worth redesigning the board?

Have you another nRF24 module that you could connect up on a breadboard to do some tests?

One of the high-power nRF24s would be better, if you have to buy something.

2.4GHz wireless and antennas are the next best thing to black-magic. I would not waste time trying to connect an external antenna to a module with a PCB antenna.

...R