CC1120: Choose IF Frequency

For low datarates, keep the IF at default.

What is the reason for operating without preamble/ sync?

With a RX BW  =12.5 kHz, have you checked that you don't have a small offset in the RF frequency (or more importantly, an offset between the RX and the TX side)  

Hi TER,

-"What is the reason for operating without preamble/ sync?" I create packet is 794 bits preamle 0x55 + 6 bits sync 0x3F + 14 bytes data, So I will handle to catch my packet in MCU.

- Offset between the TX and  the RX side always < 200Hz

Thank you for response.

Vu.

CC1120 is designed to use preamble and sync. Since you wrote that you are not using preamble/ sync, does that mean that you are using transparent mode? If possible, use he default sync word.  What is the background for using a very short sync word and a very long preamble? 

I use FIFO mode without sync and preamble(it's look like transparent mode?).

"What is the background for using a very short sync word and a very long preamble? " Because this is model specifications of my project.

Do you have any ideas?

Thank you.

Vu,

Is this an old legacy format you have to comply with? 

I would  start with set the sync word to 0x55553F (or the last 32 bits you send)

yes,this an old legacy format I have to comply with.

when I set sync, I get 2 packet:

packet 1(OK): ....555557F01630C618C3...

packet 2(NG):...5552AAFE02C618C318630C618C7006DEC100

Second packet is wrong 1 bit in preamble.

Sometime, 14 bytes data isn't receive enough.

Thank for response!

Vu,

Do you use fixed packet length (I assume you don't have a length byte?)

Hi TER

I config mode as below:

// Variable length mode
dmy = 0x20;
write_cc1120_single(PKT_CFG0, &dmy);

dmy = 0xFF; 
write_cc1120_single(PKT_LEN, &dmy);

Vu,

Meaning that you have a length byte? You don't describe a length byte as part of your payload. 

Hi TER, 

I understood.

when I set fixed len mode, PKT_LEN = 14( = Payload len) data sometime just 0x55, i can't see my payload,

when I set infinity len mode or without preamble, sync => data read from RX FIFO continuos(data+noise), but the last byte of payload sometime wrong(~40%).

Side TX : after send the last byte of payload => IDLE.

Thank you,

Vu.

Could you share the register settings you used for the latest test?

Hi TER, This is setting:

The last byte wrong because TX side:

As you can see, the last byte data when I send continuos( pointer 1) data OK, when the last byte data send => IDLDE then data will be wrong, noise is generate(pointer 2).

Can you explain it?

First settings: Why have you set the sync word differently on the RX and TX side?

Why have you set SYNC0 to 0x7F and not 0x3F?

Hi TER,

Sorry, At TX side I change: 

// Set no hardware preample and sync
dmy = 0x00; // No Preamle
write_cc1120_single(PREAMBLE_CFG1, &dmy);
dmy = 0x03; // No Sync
write_cc1120_single(SYNC_CFG0, &dmy);

Preamble + sync : ...0101 0101 0111 1111 : 0x55, 0x7F

TX side I'm not set Preamble + sync, I just write data ...0x55, 0x7F into FIFO to transmit it.

RX side receive normal.

Now, I want to know the pulse noise at the last byte of packet.

Thank you,

Vu,

Have you seen issues caused by "noise"?

The plots you have posted: What is the "y" axis, is it output power or deviation? Is the noise independent of the PA ramp settings? 

Hi TER,

It's output of AF level, about 2Vpp is output when AF LEVEL = 0 dB.

When I change PA ramp setting, It wil be change.

I have a new question. In RX side, If no signal at input of RX then value of register RSSI is 0x91 => -111dBm, I want to increase sensitivity, about -120 or lower when no signal at input RX,

Which register I can set to get this.

Thank you, 

Vu

RX: Not exactly sure what you mean. My understanding is that you have your DUT, you have no known input on the antenna port and you are not able to read a RSSI lower than -111 dBm? Do you have an antenna connected? In that case what you are seeing is the noise floor where you are located. You can see if that is the case by moving the DUT into a RF shield and see if the RSSI drops.

TX: Not exactly sure what you mean here. First, Not sure what you mean by AF level and where exactly you do this measurement. Secondly, why do you do this measurement? We are never looking at the signal in the voltage domain. 

RX: I have a Radio communcication tester, Tester connect to RX via coaxial cable.

Then I set input power RX, When noise in RX, I'm not able to read RSSI lower than -111dBm.

When I change channel RF, RSSI still -111dBm.

TX: I think because it make RX receive packet wrong(at end of packet)

To fully understand what you are seeing I believe I have to run some measurements. Due to the covid-19 situation I try to limit the number of days in the office. Would you be able to disclose the potential volume for this project? If you don't want to share it in a public forum, send be a friend request. 

Hi TER,

Thank for your support!

In RX, I found issue from my hardware, so I can't read correct value RSSI.

In my code, when I read RSSI interval 10ms, RSSI return about -123, -124dBm.

When I read RSSI interval 1ms, RSSI return -123, -124, sometime is -60, -61 dBm.

Because I read RSSI value too fast, right?

I want to update RSSI value as quickly as possile.

Thank you. Vu

Have you looked at and calculated the RSSI response time according to https://www.ti.com/lit/pdf/swra413?