subsidiary carrier wave

user3515304

Prodigy 110 points

Other Parts Discussed in Thread: CC1125, CC1120

there is a subsidiary carrier wave occur when CC1125 transmit a carrier wave complete,why?

over 8 years ago

0 PM over 8 years ago

TI__Mastermind 27145 points

Hi,

Did you test at other frequencies (for example 459MHz & 461MHz)? Does the spur follows the carrier ( same Delta in frequency)? Just I want to make sure that the Spur you are seeing from the board not from external sources.

This spur could be related to the Reference crystal.

What crystal/TCXO freq is being used on the board?

Is this a conductive or radiative measurement?

Thanks,

0 user3515304 over 8 years ago in reply to PM

Prodigy 110 points

Hi,

Thanks for your reply.

we used 38.4MHz crystal on our board.and,this is a conductive application.

Thanks.

0 TER over 8 years ago in reply to user3515304

TI__Guru**** 317180 points

When reporting a spur, please use a marker clearly showing the frequency. Also read 4.14 in the datasheet (www.ti.com/.../cc1125.pdf)

0 user3515304 over 8 years ago in reply to TER

Prodigy 110 points

Hi,

the picture upside is a screen of no unmodulated carrier wave with it's center frequence on 410MHz.As you can see,there are more than one wave crest,is it normal?

And ,the follow picture is a modulated carrier wave with the same parameter.

0 Sverre over 8 years ago in reply to user3515304

TI__Mastermind 39860 points

In the top plot I think you are transmitting a 0-1 sequence (e.g a preamble). When you have low RBW you will observe the the line spectrum. Assuming you send a 0-1 sequence you will see spikes at a distance given by the modulating frequency which is 50 kHz at 100 kbps.

You get the settings to transmit a CW (carrier) from SmartRF Studio. If you use packet mode and start TX without anything in the TX FIFO you will transmit a preamble.

0 TER over 8 years ago in reply to user3515304

TI__Guru**** 317180 points

The upper picture looks like you send a preamble. Are you sure you are actually sending a CW?

0 user3515304 over 8 years ago in reply to Sverre

Prodigy 110 points

You are right,The multiple wave crest is caused by transmitting a preamble indeed.But,when i set up the PREAMBLE_CFG1 register to 0x00 (e.g no preamble),it can't see any carrier wave occur. is that the property of CC1125?And,I want a pure unmodulated carrier wave,What should I do?
Thanks.

0 TER over 8 years ago in reply to user3515304

TI__Guru**** 317180 points

How to send a CW with CC1120/ CC1125 is covered multiple times on the forum. SmartRF Studio will tell you the register you have to set to send a CW.

0 user3515304 over 8 years ago in reply to TER

Prodigy 110 points

Hi,

the situation of subsidiary carrier wave is still after new try which avoid the spurious emissions.there is a spurious emissions occur only when the RF channel is closer than 1 MHz to multiples of XOSC in TX,according to the description of 4.14 in the datasheet.But,when my frequence is set to 422.625MHz,and XOSC is use 40MHz crystal,the spurious emissions occur still.

is there any good advice for me?

thanks.

0 TER over 8 years ago in reply to user3515304

TI__Guru**** 317180 points

Do you have a plot of how it looks like?

0 user3515304 over 8 years ago in reply to TER

Prodigy 110 points

Most of the situation,it occur in the end of main carrier wave,and it will occur in the start of main carrier wave sometimes.

thanks.

0 TER over 8 years ago in reply to user3515304

TI__Guru**** 317180 points

e2e_plot2.WMF

A spur will not move around randomly, I don't get a spur on the given frequency.

0 user3515304 over 8 years ago in reply to TER

Prodigy 110 points

Hi,

if the plot come from SmartRF which show in the e2e_plot2.WMF?Can you show me all registers content of the CC1125 at the moment you send?i mean,if you can read out all the registers and show me the content when CC1125 prepare sending data right away?

thanks，

0 TER over 8 years ago in reply to user3515304

TI__Guru**** 317180 points

I used SmartRF Studio to set up the transmission sending a CW. The register settings are equal to the 1.2 kbps setting in SmartRF Studio

0 user3515304 over 8 years ago in reply to TER

Prodigy 110 points

Get it,
Thanks

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subsidiary carrier wave