CC1120 169MHz problem with output TX power

Measure the output power at the 50 ohm connection point (SMA).

Keep the PA_CFG1 and PA_CFG0 values as default specified by SmartRF studio.

For changing the output power. Change the PA_CFG2 register only.

Regards, Richard

Hi Richard,

I did measure  output power at SMA connector as well (before I removed cap C174 and measure directly there), and result in magnitude will not change much from posted screenshots in my first post. (I am keeping default values (after restart) for PA_CFG1 and PA_CFG0 while changing PA_CFG2).

I am losing -35dBm somewhere. How can I troubleshoot this? Any advices?

Now I am not sure if this is software or HW problem? (Got 6 assembled PCBs and all of them behave the same).

I doubt this is a software issue since you are sending on the correct frequency.

But what you can do is to control the CC1120 with SmartRF Studio via either a CCDebugger or a TRX EB. Then you will be able to check the board with known good software.

Check the spectrum analyzer setup with  known good source. Have you accidental managed to use an attenuator?

I haven't double checked the component values but it looks ok. double check that you have mounted the correct values and that the soldering is ok. Measure on the output of the SMA since the second point you have measured on is not a 50 ohm point and I'm not sure what to expect in this point (but I would expect a larger fundamental)

Thank you.

I did wired RF board to TRX_EB in order to be sure it is not a software problem.

And transmiting from SmartRF studio behaves the same like from MCU on RF board. (The same problem when transmitting at +15dBm I got - 40dBm on scope). So I can confirm this is not a software problem but HW. And I measure output power as you suggested - at the 50 ohm connection point (SMA):

Now what I am thinking to measutre some voltage level and compare with orginal RF169 dautherboard from TI. (Which is working fine, and on spectrum analyzer I can see right values). - I do not use attenuator. (I did tried with different cables withour attenuators).

So I think it will be something wrong with components.

What components shall I double check (the one that influent  TX power output)? See included schematic:

One thing I did extra, was to wire up RESET pin to Vdd_reg. (forgot during desing to connect RESET pin to 3v3). Could this cause output power problem?

It sounds like you have an issue either with assembly or soldering.

You get about 45 dB less output power than expected. For me it sounds like (at least) one component in the signal path is missing or not soldered properly. Have you measured that you have the correct DC voltage on L171 (3.3 V )? Is the ground paddle on the chip properly soldered to ground? 

On L171

1) when transmissing packets:

I measured 2.94V, where battery voltage 3.18V  and measured also on  Vreg is also 3.18V. so there is voltage drop to 0.24V when sending packets.

2) wheb not sending packets:

I measured 3.12V, where battery voltage 3.18V  and measured also on  Vreg is also 3.18V. so there is voltage drop to 0.6V

I compare to origial RF dautherboard with SmartRF and there is small voltage drop as well when transmitting packets.

But there is no voltage drop when not sending packets. What can I check more with voltmeter?

"Is the ground paddle on the chip properly soldered to ground? "

How can I check/test this? It is under the IC transceiver.