CC1200 working Frequency Deviation range

Alex Strelbytskyy

Expert 1910 points

Other Parts Discussed in Thread: CC1200, CC2500, CC1101

Hi TER,

When we tested CC1200 based modem with existing modems using 4GFSK, we discovered that it is very sensitive to the tolerance of Frequency deviation. For the settings: frequency 415MHz, bit rate 19.2 kbps, 4GFSK, Freq.Deviation 4.8kHz, RxFilterBW=28kHz the working interval for frequency deviation = 1.9kHz, we expect ~3.6kHz. What parameters should we adjust?

Thanks,

Alex

over 9 years ago

0 TA12012 over 9 years ago

TI__Mastermind 36375 points

When you say 19.2kbps are we talking 9.6ksymbols/s => 19.2kbps.

Anyway at 9.6ksymbols/s and 4.8kHz deviation you are a modulation index of 0.33. This is too low and you will degrade the RX performance. We do not recommend going below 0.5 and you will find our recommended settings are 0.5 and slightly above.

If you are actually talking about 19.2ksymbols/s becoming 38.4kbps effective, then the modulation index is 0.166.

I recommend a frequency deviation of 7.2KHz or greater.

Regards,

/TA

0 Alex Strelbytskyy over 9 years ago in reply to TA12012

Expert 1910 points

Hello TA12012,
We use bit rate 19.2kbps (9.6 ksymbol per second). The frequency deviation was selected to fit emmission mask and can't be changed. Many narrow band modems for survey applications use even smaller frequency deviation.
Thanks,Alex

0 TA12012 over 9 years ago in reply to Alex Strelbytskyy

TI__Mastermind 36375 points

What do you mean when you write:

RxFilterBW=28kHz the working interval for frequency deviation = 1.9kHz

Can you send a plot of the TX mask?

Regards,
/TA

0 Sverre over 9 years ago

TI__Mastermind 39860 points

The way I read your post is that the link works if the transmitter use +/-4.8 kHz deviation, but you get degraded performance (or even no link) if the transmitted deviation is lower than this by more than 1.9 kHz (i.e. deviation of +/-2.9 kHz or less). Is my understanding correct?

A low deviation results in a low modulation index and this will affect performance. One thing to try is to program a lower deviation on the RX side. This might affect sensitivity if the deviation gets to large though.....

What's the background? Are you targeting backwards compliance with existing systems with wide tolerance on the frequency deviation? If you use CC1200 on both sides of the link there will the transmitted frequency deviation will not have a wide tolerance.

0 Alex Strelbytskyy over 9 years ago in reply to Sverre

Expert 1910 points

Hi Sverre,
Right, we want to have our new CC1200 modems compatible with existing our and other producers’ modems. When we reduce Frequency Deviation, modem receives data from one modems (low frequency deviation << 4.8kHz), but doesn’t receives form others (most popular frequency deviation 4.8kHz).
Two our new CC1200-based modems work fine.
How we can reduce tolerance of frequency deviation during receiving?Thanks.Alex

0 Alex Strelbytskyy over 9 years ago in reply to TA12012

Expert 1910 points

How Tx mask can solve compatibility problem?

0 TER over 9 years ago in reply to Alex Strelbytskyy

TI__Guru**** 317180 points

The CC1200 is not designed for large deviation variation.

You may try to program CC1200 with a deviation that is between min and max and also play with SYNC_THR (1-2 step up or down)

0 Alex Strelbytskyy over 9 years ago in reply to TER

Expert 1910 points

Thanks, I will try.

0 Alex Strelbytskyy over 9 years ago in reply to TER

Expert 1910 points

Hello TER,
Unfortunately, it doesn’t work; we have bad reception from both models.
If being received data packet has long preamble, is it possible to switch frequency deviation on fly (during receiving preamble) in order to be taken in affect during current reception? Is frequency deviation latched when transceiver goes from IDLE to RX state?
Thanks,Alex

0 TER over 9 years ago in reply to Alex Strelbytskyy

TI__Guru**** 317180 points

Which deviations do you want to support? I could not find the exact numbers when reading through the thread again.

0 Alex Strelbytskyy over 9 years ago in reply to TER

Expert 1910 points

CC1200-based modem has frequency deviation 4.8 kHz and working range +-0.8 kHz, that is good for one model of narrow band modems. Other modem that is supposed to be compatible with CC1200-based has frequency deviation 3.1 kHz.
Is it possible to switch frequency deviation on fly?

0 TER over 9 years ago in reply to Alex Strelbytskyy

TI__Guru**** 317180 points

It is advisable to go to IDLE before changing the deviation to ensure that the modem is reset and no old data is in the pipeline.

Would you be able use the custom frequency modulation (analog FM) feature to detect the deviation, IDLE, switch deviation?

0 Evangelos Kaloudiotis over 9 years ago in reply to TER

Prodigy 180 points

Hello,
I am trying something different. I am trying to port some CC1101 (identical register map with CC2500) settings to CC1200. However (and that's normal) not alla register names are the same. What are the corresponding registers (if it works that way) for the following registers:
CC2500_MCSM1 (I think it relates to MDMCFG1)
CC2500_PKTCTRL1 and CC2500_PKTCTRL0 (I think it relates to PKT_CFG1 PKT_CFG0)
CC2500_STATE_TX_UNDERFLOW (I think it relates to TXFIFO_UNDERFLOW )
Thank you

0 Siri over 9 years ago in reply to Evangelos Kaloudiotis

TI__Guru* 79501 points

It is not possible to make a list of which registers on the CC1101 corresponds to which registers on the CC1200. You should use SmartRF Studio for both devices when generating the registers. If you use the typical settings and just change RF parameters, all the registers related to the packet engine will be the same (variable packet length, same CRC, append status etc). The sync word is different for the two devices and the CC1200 must use the same sync as used on CC1101, since CC1101 only has two sync word registers.

Siri

Sub-1 GHz

Sub-1 GHz forum

CC1200 working Frequency Deviation range