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Harmonic problems in 2.4Ghz antenna

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DNA2683

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Hi All,

I designed a small PCB with BLE (2.4Ghz antenna ). Just for make thing clear i didn't designed the RF part only the digital.and im not an RF guy :) so ill be glad to get some help from you guys.

I using TI CC2640 as transceiver and antenna on chip . when i send the board for EMC test the lab told me that i have few harmonics higher then 40dbm (maximum power aloud in 40 dbm) i added some pictures of the results.
The RF circuit pleased on the CS(layer 1) with grounding layer (layer 2) .The impedance of the RF transmutation line is 50 hoam.

what can be the source of this harmonics ? how can i trace the source?

ill be glad for your help guys, if there is more information that needed please ask and ill upload it.

TNX

image007.jpgimage008.jpg
 

Confusing post. Non of the emissions seems to be related to transceiver operation. Particularly they are unlikely radiated by a 2.4 GHz antenna, in so far the thread title is probably missing the topic.

There is a certain possibility that the 24 MHz RF oscillator or ARM processor power supply is the interference source, which would indicate a really bad circuit layout. It can be checked by selectively deactivating oscillators, switching CPU frequency etc. A simple spectrum monitoring device is required for this kind of tests.

The other explanation is that you have additional component that are generating the interferences. 108 MHz respectively 12 MHz as a possible fundamental aren't used inside the CC2640 at all. A good tool to locate interference sources is a small pick-up coil.
 

FvM said:
Confusing post. Non of the emissions seems to be related to transceiver operation. Particularly they are unlikely radiated by a 2.4 GHz antenna, in so far the thread title is probably missing the topic.

There is a certain possibility that the 24 MHz RF oscillator or ARM processor power supply is the interference source, which would indicate a really bad circuit layout. It can be checked by selectively deactivating oscillators, switching CPU frequency etc. A simple spectrum monitoring device is required for this kind of tests.

The other explanation is that you have additional component that are generating the interferences. 108 MHz respectively 12 MHz as a possible fundamental aren't used inside the CC2640 at all. A good tool to locate interference sources is a small pick-up coil.
Click to expand...


Hi FVM

thank you for your quick response .

The board include more components such as external ARM processor.and MEMS component.

There is 2 external oscillators on board :
32.768 KHz and 24MHz for CC2640.

for the external ARM i used the builtin oscillator.

regarding the power . the RF guide add decoupling capacitors.

there is a way to trace this kind of problem without using spectrum monitoring device?


TNXCapture1111.JPG
 

there is a way to trace this kind of problem without using spectrum monitoring device?
Click to expand...
How? you either will try to locate the emission maximum with a field probe or modify circuit parameters during the radiated emission test. If you can't perform pre-compliance or at least interferer identification measurements yourself, you'll do them in the EMC lab and pay per hour. Price of simple spectrum monitoring devices start at the equivalent of a few lab hours. Some RF knowledge is of course necessary to operate the instrument and understand the results.
 

could you explain your data. You say it is a 2.4 GHz communication system, but you are showing power transmitted (or leaked) only from 10 to 1000 MHz. WHere is the plat from 2 to 10 GHz, for instance?

You would need to show us your PC board layout, and any shielding you have, along with the schematic for the circuit. Most likely you cut the ground plane in a number of places--making a virtual VHF antenna of the entire board. the energy is not leaking out your antenna, but rather the entire board.

BTW, why not simply rehire the RF engineer to figure it out...this is exactly WHY you hire RF engineers instead of trying to make do without one.
 
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    FvM

    FvM

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I see some FM and TV Broadcasting signals only..
 
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    FvM

    FvM

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I see some FM and TV Broadcasting signals only..
Click to expand...
Yes, that was my first guess too. But hard to believe for measurements made by a professional EMC lab.
 

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