Re: [Discuss-gnuradio] UHD vs. USRP2 driver questions

[Josh Blum]

On 11/29/2011 02:38 PM, Kevin Tien wrote:
> Hi,
> 
> We're using USRP2s with the RFX2400 daughterboards, and we've recently
> switched from the old USRP drivers to the UHD drivers as per general
> recommendation. However, we've run into a few problems that have us
> stumped:
> 
> 1) Previously, our receiver gains were set to 0 dB and we had no
> problem receiving a signal with >30 or 40 dB SNR. However, now the UHD
> receiver blocks need specified gain around 30 or 40 dB to achieve this
> same performance; did baseline values change?
> 

Are you selecting the correct antenna? Its possible the default RX
antenna setting is different.

> 2) As far as we can tell through searching the Internet, the sampling
> rate in the Tx/Rx blocks has replaced the decimation and interpolation
> fields from the legacy blocks. But what exactly are we specifying with
> the sampling rate now? Is it the sampling rate the rate at which the
> transmitter transmits samples, with interpolation assumed if the data
> going into the block isn't throttled? In which case, would higher
> sampling rate imply lower 'interpolation' rate? Bottom line, we have
> no idea how to play around with the sample rate, or how important it
> is.
> 

The sample rate is the rate of samples between host and USRP.

on RX: sample_rate = dsp_rate/decimation
on TX: sample_rate = dsp_rate/interpolation

-josh