New to SDR, BladeRF 2.0 xA4 gain question

[danKen01]

Hello all,

I am developing a simple SDR transmission platform for learning purposes using Nuand's BladeRF 2.0 xA4. I have been successful in getting the device to transmit using a boilerplate, but have been confounded by the gain setting.

Using the terminal bladeRF-cli program the software reports (by using the command print tx1 gain) that the device (2.0 xA4) has a gain range of -23.5 to 66. Is this in db? A gain of 66 db seems like it should be consuming a fair amount of power but the maximum output of the device is only 8dbm according to Nuand's datasheet. Am I misunderstanding something fundamental here? Is the device outputting a -58dbm signal (8-66) with 0 gain? Or is the gain range smaller and the bladeRF-cli client is feeding me bad information.

If someone could clear my misunderstanding up or point me to some resources for further reading I would greatly appreciate it.

[robert.ghilduta]

On the bladeRF 2.0 micro, a TX gain of 66 should correspond to a TX DSA of 0. One thing to check is the magnitude of the IQ samples. The bladeRF 2.0 micro's full scale IQ samples are in a range of [-2048, 2047].

[ghbjakef3]

I've been assuming that set_gain(channel, 66) was about 10dBm. So from what you guys are saying, this assumption is correct? Then, I could say that a set_gain(channel, 56) would be about 0dBm. I mean of course, it isn't calibrated but just a ballpark figure is useful.

@[email protected], thanks for tracing that out. That is quite helpful! There is only one question I have. I thought last time I looked the signal traces into the AD chip were 12-bits per I and Q so how in the world does the FPGA attenuate it that much? I'm just curious how it works and hope you might tell me without having to dig through all the code like you did.

Is the device outputting a -58dbm signal (8-66) with 0 gain?

From what I understand, this is correct? Is this right?

[the_emi_guy]

Actually the AD9361 does have adjustable attenuator on tx channel, 0 to -89.75dB in 0.25dB steps.
Can this be controlled from gnuradio osmocom Sink or bladeRF-cli?

[ThunderBolt84]

According to the [libbladeRF documentation][https://www.nuand.com/libbladeRF-doc/v2 ... 9beb9e12ff], a gain setting of 60 dB approximately corresponds to 0 dBm TX power. The maximum setting of 66 dB corresponds to 6 dBm TX power - which happens to be the [official maximum spec][https://nuand.com/forums/viewtopic.php?p=7398#p7398].

I came across this with a similar question; I'm using GNU Radio with the BladeRF 2.0 xA4 but the gain setting is still the same. Hope my findings are helpful to anyone reading this thread in the future.