Author Topic: CC1125 half carrier harmonic  (Read 2494 times)

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Offline veryevilTopic starter

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CC1125 half carrier harmonic
« on: July 23, 2016, 08:37:12 am »
Hi, have a CC1125 on a project I'm working on in the 868MHz ISM band but when  I fired it up I get a really large peak at 430ish MHz it's at about -17dBm and carrier is about 14dBm.  Its way over limits for out of band power and I'm not sure where is best to look. 

Any ideas?  Thanks. 
 

Offline jmsigler

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Re: CC1125 half carrier harmonic
« Reply #1 on: July 23, 2016, 08:39:51 am »
Are you using the reference design with the saw filter?
 

Offline veryevilTopic starter

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Re: CC1125 half carrier harmonic
« Reply #2 on: July 23, 2016, 08:43:37 am »
Yeah its really close to the Cat1 reference design
 

Offline veryevilTopic starter

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Re: CC1125 half carrier harmonic
« Reply #3 on: July 25, 2016, 07:52:26 am »
I've got a screen shots of it now.

Hope this might help get a clearer idea of whats going on
 
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Offline jmsigler

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Re: CC1125 half carrier harmonic
« Reply #4 on: July 26, 2016, 12:05:01 am »
What saw are you using?
 

Offline veryevilTopic starter

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Re: CC1125 half carrier harmonic
« Reply #5 on: July 26, 2016, 07:10:04 am »
Hi, I'm using the Epcos TDK B39871B3744H110 SAW filter

Had an idea?
 

Offline jmsigler

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Re: CC1125 half carrier harmonic
« Reply #6 on: July 27, 2016, 01:22:33 am »
Well I'm wondering how your measurement is possible since the saw datasheet lists 55dB attenuation in that band... I understand that there are various factors that can degrade this figure, but It looks like the saw isn't even there.

Are you sure everything on the board is soldered right?
 

Offline veryevilTopic starter

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Re: CC1125 half carrier harmonic
« Reply #7 on: July 27, 2016, 06:04:06 am »
The SAW is in the receive path not the transmit path.   
 

Offline Gribo

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Re: CC1125 half carrier harmonic
« Reply #8 on: August 05, 2016, 06:28:59 pm »
What is the difference between your design and the reference design? Are you sure the RX path is properly decoupled from the TX path?
I am available for freelance work.
 

Offline veryevilTopic starter

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Re: CC1125 half carrier harmonic
« Reply #9 on: August 05, 2016, 06:34:14 pm »
Hi,  funny you should mention that.  After some work with an rf engineer the   track between the tx rx switch pin to the rx tx shunt cap was too long making a large inductor.

It made the output very load dependent and we had an extra filter on the output which it didn't like either. 

Need another respin to be sure but think we have it. 

Thanks
 


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