|Subject:||Re: [Discuss-gnuradio] USRP1 gain|
|Date:||Wed, 9 Oct 2013 17:20:16 +0200|
On 10/09/2013 11:03 AM, Nemanja Savic wrote:Gain is distributed by UHD starting at the antenna, and moving towards the ADC.
You are right Marcus, but it is negative gain, and I wonder why USRP source allows me to specify more than 20 db of gain for wbx, without any warning. In fact what happens when u specify some gain value, how is configuration of the path set?
In the case of WBX, the attenuator sits between two LNA modules.
And, I'll emphasize again--the way gain-control is implemented in RF circuits is with a variable attenuator. If you purchase an RF
Variable Gain Amplifier chip with a voltage-control input, it's overwhelmingly likely that the way it's implemented internally is with
a voltage-variable attenuator.
The thing to "care" about is whether at some gain-setting value 'X', is my signal-processing-chain "happy" with the results.
If you're doing things like precision power measurement, you *HAVE* to use an external calibration. You can't just play
math games with adding up nominal circuit-element gains, because each element in the gain chain that provides a gain
will have device-to-device variability of 1dB or more.
Shirleys Bay Radio Astronomy Consortium
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