Re: [Discuss-gnuradio] Gain distribution with Flex 400

[Nick Foster]

On Thu, 2011-08-04 at 12:54 +0300, Sivan Toledo wrote:
> How is gain distributed when the UHD USRP block is told to set the
> total gain to a particular value?
> 
> I am using GRC with UHD controlling a USRP with a Flex400 daughter
> board. I set the gain in the GRC block to 20dB, which results in the
> line "self.uhd_usrp_source_0.set_gain(20, 0)" in the Python output
> file.
> 
> My understanding is that the codec on the USRP has an internal PGA
> whose gain can be set between 0 and 20dB and that the Flex400's mixer
> also has a PGA whose gain can be set between 0 and 45dB.
> 
> Does this mean that I can set the gain in the USRP source block to
> anywhere between 0 and 65dB (with the driver deciding how to
> distribute the gain between the two PGAs), or is there a way to
> control separately the two PGAs?

UHD handles gain distribution generally from the front end inward, for
best NF. You can control individual gains like so:

self.uhd_usrp_source_0.set_gain(20, "PGA0", 0)

You can get a list of gain controls with:

self.uhd_usrp_source_0.get_gain_names(0)

--n

> 
> Thanks, Sivan Toledo
> 
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