Frequency offset in %XRFTEST CW testing

[Norbert Braun]

Hi,

I noted that the CW generated in the %XRFTEST TX test seems to be offset from the requested frequency. Specifically, issuing the command

AT%XRFTEST=1,1,20,8500,-50,0,4,0,0,0,0,0

generates a CW wave with a frequency of approximately 850.255 MHz (255 kHz off). Changing the requested frequency seems to leave the offset constant.

I am using a PCA10090 devboard (v0.8.5) with modem firmware mfw_nrf9160_1.2.0. Another devboard with modem firmware mfw_nrf9160_1.0.0 shows the problem as well.

Switching to generating a modulated signal, e.g. with

AT%XRFTEST=1,1,20,8500,-50,0,0,12,0,0,0,0

generates a spectrum that is nicely centered around 850.0 MHz, so this does not seem to be a hardware issue.

Is this a known issue, or perhaps expected behavior? I could not find anything in the documentation of the %XRFTEST command.

Best regards, Norbert

[Håkon Alseth]

Hi Norbert,

 

 

Is this a known issue, or perhaps expected behavior? I could not find anything in the documentation of the %XRFTEST command.

My apologies for the inconvenience, and thank you for reporting this back to us!

Given that the second command with modulated output is spot on frequency-wise; It sounds like you have stumbled upon a issue on our side. I will check internally and confirm the issue, as I unfortunately do not have access to a spectrum analyzer today, and get back to you soon (a couple of working days).

 

Kind regards,

Håkon