Re: [Discuss-gnuradio] How to capture the Rx data using uhd_rx_cfile and agree with the uhd_fft Scope mode data

[Josh Blum]

On 09/27/2012 02:42 PM, LD Zhang wrote:
> Yes. I can understand the LFRX does not have any adjustable gain. But what
> comes out of the USRP source should be samples already digitized. Surely
> there is gain to be adjusted before the ADC. According what I see, it is
> from 0 to 6dB (in voltage?). I don't see how this can be inserted into the
> USRP source block.
> 

You are correct. The N210 has a 6db digital gain. Attached is a GRC
flowgraph that loopsback TX and RX with Basic daguhterboards. You can
see the digital gain slider in action.

The gain parameter in the GRC block is a amalgamation of ADC and RF
frontend gain elements. The API also allows for individual control, but
this level of control is not available in the GRC gain parameter.

> Also I have some related questions:
> 1. the float numbers out of the USRP source block appear to be in volts.
> There is no indication of what units it is in.

They are in counts where 1.0 corresponds to fullscale ADC.

> 2. Is there any way of specifying bandpass filters before the ADC? This
> would probably be independent of the LFRX, but something on the motherboard
> before the ADC? I do see an option in the USRP block that seem to do this.
> However this bandpass may be after the ADC?
> 

The bandwidth parameter is for configuring frontend bandwidth filters.
You can find out here which boards are configurable w/ this feature:

http://files.ettus.com/uhd_docs/manual/html/dboards.html

-josh

> Thanks,
> 
> LD
> 
> 
> On Wed, Sep 26, 2012 at 11:55 AM, Josh Blum <address@hidden> wrote:
> 
>>
>>
>> On 09/26/2012 01:36 AM, LD Zhang wrote:
>>> Hi,
>>>
>>> I did try and made a GRC example of using a USRP Source and a fft sink,
>>> scope sink, and a file sink to test out the idea.
>>>
>>> When looking at the scope sink, the data is about +/- 2x10^-4. I changed
>>> the gain of the USRP source block to 20 dB. But nothing happened to the
>>> signal amplitude. How is this possible?
>>>
>>
>> You mentioned LFRX? There are no configurable gain elements for the LFRX
>> daughterboard.
>>
>> If this helps, the various gain ranges are listed for various
>> daughterboard frontends here:
>> http://files.ettus.com/uhd_docs/manual/html/dboards.html#basic-rx-and-lfrx
>>
>> -josh
>>
>>
>

n210_rx_ADC_gain_slider.grc
Description: application/gnuradio-grc