nRF905 poor reception

[Witek]

Hi, I am developing a product for the 433MHz band. Due to the space constraints I had cut the ground plane to very small and also had to rearrange the components away from the suggested layout. The antenna is a spring wire soldered into the PCB. I used a Pi matching circuit to get the power out in the air. The device talks to a base which has a proper whip antenna, with layout as per suggested layout.

As measured on spectrum analyser we get a very good signal from the device (in fact better than the base whip). The problem is the reception. I get nowhere near the range on RX as I get on TX (the messages from the device are received from a longer distance, the device can receive messages from a shorted distance only). Could anyone please explain this phenomenon to me, or better still provide a solution to get the RX range as well.

I guess I should also mention that the device is mounted on top of an aluminium block.

Let me know if you have any questions with regards to the setup.

Thanks Witek.

[Kenneth]

Hi, I suggest you look into possible noise sources on the board, for instance maybe you have some serial interface active toggling, or other digital lines sourcing or sinking high current during reception. This can reduce the sensitivity. You should find some PCB guidelines in the datasheet for design recommendations.

[Witek]

Hi Kenneth, Thanks for your responce. Yes, you are right, there is a noise isssue on my board. In my case the trouble is a switch mode regulator. From your experience would you be able to tell whether the sensitivity is more affected by the radiated or conducted noise. Due to size constraints the switcher is located quite close to the radio chip. Thanks Witek

[Kenneth]

I don't work with hardware on a daily basis, but I have seen both can have an effect.