Re: [Discuss-gnuradio] USRP B210 TX gain

[Marcus D. Leech]

On 08/02/2015 03:01 PM, Samith Abeywickrama wrote:

Hi,

I am confused with 89dB tx gain of USRP B210 and what is the meaning of 89dB gain? How this value relates to maximum output of 50mW in B210? Because this value is too much high, as a example: If the RF output power of AD9361 agile transceiver is -29dBm and after we apply 89dB gain, transmit power should be 50dbm, But 50dBm is too much higher than 50mW.

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Best Regards!

Samith

The maximum output power of the AD9361 is about +17dBm.

Gain control is implemented as attenuators in the gain chain, so that 89dB of gain-control range should be applied to the maximum output power at any
  given frequency, so that a setting of 0dB gain means that, notionally, your output power is  +17dBm - 89dB = -72dBm, and at 89dB "gain", your output
  power would be +17dBm.

In RF circuits, it's very typical to use variable attenuators to effect gain control, so that the individual gain stages operate at fixed bias and matching
  levels, and the inter-stage attenuators collectively effect some range of gain control for the entire chain.