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 <j...@ettus.com> 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
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