RTOS/CC1350: CC1350 Launchpad Range Issues

Mobashir,

Which specific launchpad are you testing with? Some of them have an RF switch on them and this switch needs to be configured correctly before testing. The typical isolation of an RF switch is 20-30dB and that is exactly what you are missing.

Regards,
/TA

Hi,

Thanks for the quick reply. I'm using CC1350 Launchpad ( LAUNCHXL-CC1350 EU Rev 1.2). If it is a switch issue, how can we configure it? We have already connected the external antenna capacitor to isolate onboard antenna.

Best,
MM

- Do you have access to a spectrum analyser enabling you to measure the output power you have on the antenna connector?
- The CC1350 LP uses a switch to select between the 2.4 GHz and 868/915 MHz path. Is this set correctly?
- Have you tested with SmartRF Studio? Studio sets up the switch correctly in the "configure target". Remember to set the same DIOs in your code.

Hi,

1. No I don't have a spectrum analyzer. However, my question was regarding the difference in the observed RSSI values for a pair of transmitter and receiver. When using smartrf it is around -14dBm. However when using the ti rtos example, the rssi printed out is -40dBm.

2. Yes, it is set correctly. We have the following lines in the BoardGpioInitTable
CC1350_LAUNCHXL_DIO1_RFSW | PIN_GPIO_OUTPUT_EN | PIN_GPIO_HIGH | PIN_PUSHPULL | PIN_DRVSTR_MAX, /* RF SW Switch defaults to sub-1GHz path*/
CC1350_LAUNCHXL_DIO30_SWPWR | PIN_GPIO_OUTPUT_EN | PIN_GPIO_HIGH | PIN_PUSHPULL | PIN_DRVSTR_MAX, /* External RF Switch is powered on by default */

3. Yes, I tested with the SmartRF Studio and exported the same smartrf-settings.c and smartrf-settings.h file to the ti rtos project. It is supposed to transmit at 14dBm.

I'm not sure what could be wrong. I have also defined CCFG_FORCE_VDDR_HH = 1 in the ccfg.c file.

Best,
MM

Did you test the example without modifying any code?

Hi,

Yes, I tested with the unmodified example that prints the rssi of each received packet.

An interesting observation: I used ti-rtos example as transmitter and used Rf-Studio to log down the packet and the corresponding signal strength. Rf-Studio prints -14dBm in comparison to the dual mode concentrator example that prints -40dBm. Looks like the transmitted signal strength is the same and Rf-Studio just prints stronger rssi values. Is it true?

Best,
MM  

You write " dual mode radio example". Exactly which example are you referring to here? I want to test this out of the box to see what I get.

Its the rfWsnDmConcentrator and rfWsnDmNode.
I have exported the smartrf-settings for the 2.5kbps over 868Mhz.

I also did another test with nodes roughly 400m apart. The rfWsnDmNode was transmitting every second while one node was running rfWsnDmConcentrator to log the rssi values and another running SmartRF Studio to log the packets. The SmartRF Studio was able to receive almost all the packets while rfWsnDmConcentrator received nothing. Although it was the same transmitter sending periodic packets.

I have to dig a bit on this one. I get the same as you, out of the box code gives a lot lower RSSI than SmartRF Studio even through they should give the same result.

Thanks. Looking forward to your response. Meanwhile, I'm buying some LAUNCHXL-CC1350-4. Hopefully the range is better than a 868MHz Launchpad. What do you suggest? Recommendations on an external antenna would be great! :)

Why do you expect better range with LAUNCHXL-CC1350-4? I assumed you wanted to use the 868 MHz band since your first tests were done on this frequency?

I did a quick test of the rfWsnConcentrator and rfWsnNodeBleAdv examples in simplelink_cc13x0_sdk_1_50_00_08 and these looks like give a more correct RSSI. Could you test with these?

Hi,

Were you able to find some insights on why it happens? I also observed that the problem exists only at the receiver side.

I setup a transmitter running rfWsnDmNode. I was able to receive the packets on a receiving node running SmartRF Studio while the rfWsnDmConcentrator received nothing for the same transmitting node.

Is there some thresholds regarding RSSI values to detect an incoming packet for ti RTOS that needs to be set? Ti RTOS observed very weak rssi and might drop packets thinking it to be noise?

Best,
MM

I agree that this is a receiver issue. I have filed a ticket on this and have sent a mail to the group that makes these examples but haven't gotten any feedback. At first look I could not see anything in the code that could explain this but based on the results I assume that some setting is set a bit strange.

Thanks, please do let me know. I'm working on it to find out the issue myself. Any hint/help would be appreciated.