On 10/09/2013 11:03 AM, Nemanja S. wrote:
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?
Gain is distributed by UHD starting at the antenna, and moving towards
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