Re: [Discuss-gnuradio] bug with gain setting in usrp1?

[Josh Blum]

On 05/29/2013 11:53 PM, Wolfgang Buesser wrote:
> Hmm,
> 
> I don't think so:
> 
> What I apply to board A ADC0 shows up on scope0, and what I apply to board A 
> ADC1 shows up on scope1, so there are definitely two different ADCs involved.
> Looking at the scope traces they are connected as set by the line 
> self.uhd_usrp_source_0.set_subdev_spec("A:A A:B", 0) 
> i.e:
> DDC-channel0, input I from board A, ADC0
> DDC-channel0, input I from board A, ADC1
> 
> Both Q-inputs to GND
> 
> It appears, that the gain settings are somehow skewed up.
> I am sure that the gain for both ADCs attached to same LFRX-board got be set 
> individually.
> Do I need a special FPGA code?
> 
> 

The good news is that there is already software control for this. The
bad news is, there isnt an API to expose this edge case of ADC as two
unrelated streams with individual gain. See:

https://github.com/EttusResearch/uhd/blob/master/host/lib/usrp/usrp1/usrp1_impl.cpp#L464

-josh

> 
> Wolfgang
> 
>> Those are two DDC channels, derived from the same physical, analog, hardware 
>> and ADC.
>>
>>
>> The LFRX itself has no gain-setting device, but the ADC does, so when you 
>> set the gain on the ADC, you're setting the gain for both DDC-derived 
>> channels.
>  
>  
>>> on May 29, 2013, Wolfgang Buesser >><address@hidden> wrote:
>>> Hi,
>>>        I am having problems with the gain-settings on the RX-channels of 
>>> usrp1
>>>        My USRP1 is populated with 2 LFRX and 2 LFTX.
>>>        
>>>        I want to use 2 DDC-channels each connect to one 2 ADC of 
>>> LF-RX-Board A.
>>>        I have generated the following code with grc.
>>>        
>>>        When apply a signal of roughly 11MHz I see the mixed signals on each 
>>> scope.
>>>        The relation to the inputs is o.k.
>>>        
>>>        The gain-settings are however not as I expect:
>>>        self.uhd_usrp_source_0.set_gain(6, 1) affects both channels while 
>>> self.uhd_usrp_source_0.set_gain(6, 0 has no effect.
>>>        
>>>        From what I rememeber that was different in the pre-uhd-times.
>>>        
>>>        Any hint, on how I can set the gains for both channels independently?
>>>        
>>>        Thanks
>>>        
>>>        Wolfgang
>         
> 
> 
> 
> 
> 
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