[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Discuss-gnuradio] USRP1 gain

From: Nemanja Savic
Subject: Re: [Discuss-gnuradio] USRP1 gain
Date: Wed, 9 Oct 2013 17:20:16 +0200

Thank you Marcus, I think I can say that i learned something today.
Just for clarification: USRP or UHD knows the gain of all components in the rx chain of wbx. If i specify for example 12 db of gain, and the gain of the chain without attenuator is for example 25 db, it will try to set attenuation to 13 db. For values greater than 25 db, it will adjust pga on USRP main board.


On Wed, Oct 9, 2013 at 5:11 PM, Marcus D. Leech <address@hidden> wrote:
On 10/09/2013 11:03 AM, Nemanja Savic 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 the ADC.

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.

Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium

Nemanja Savić

reply via email to

[Prev in Thread] Current Thread [Next in Thread]