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CC1120: 434 <-> 868 conflicting each other when used in the same board?

GGA
Genius 3985 points
Part Number: CC1120

Hi,

we need to design a new system which contains both 434Mhz narrow band (CC1120) and a mesh network based on 868MHz, 27dB PA (CC110x + FEM)

They work on their own antennas (wire or PCB), but async. to each other .
The 434Mhz doesn't know about the 868Mhz and vice versa: there is a Linux based SOM controlling the modules, but the modules just receive/send data to the SOM, the modules themselve organize the RF part.

I'm unsure: what will/can happen and how to avoid it? What if e.g. 434Mhz sends something and 868MHz is just receiving something: won't the 434MHz harmonics harm that process?

thanks

  • 0
    TI__Guru**** 317180 points

    - Meaning that the 868 MHz module is not using LBT? 

    - Have you measured the energy (conducted) from the 433 MHz module on the frequencies the 868 MHz system operate on (or a similar 433 MHz module) ? The 2. harmonic of the 433 MHz will be directly on the 868 MHz band meaning that it the energy received from the other system will be limited. 

  • 0 in reply to TER
    Genius 3985 points

    - in fact the 868 is not under our control as its a ready-to-use-mesh (TinyMesh) module from a company in your neighbourhood ..;-). They won't use LBT as I know and ETSI nails us to 869.4-869.65 MHz

    - I did some measures meanwhile: the energy of the 434 at 2nd harmonic is at ~70-80dBc from carrier. Means that the 434 would destroy almost every packet of the 868 if the 868 works on exactly 2x434.
    Good news is that we are narrow enough that if we stay ~40kHz away from that 2nd-harmonic point, we are almost safe. And we know exactly what frequencies on 868 will be used, so even with our hopping scheme at 434 we can avoid these frequencies.

    But I found out that only if I start TX, the overall noise floor (on all frequencies) increases (conducted) by 5-10dBm (from ~-100 to -92) - is that 'normal' or is it a measurement issue?

  • 0 in reply to GGA
    TI__Guru**** 317180 points

    If you use a fairly wide span and a small RBW ensuring that you both have the fundamental and 2. harm on the same screen for the 433 MHz (if possible): Is it the phase noise you see when you start TX?