On 08 Jan 2013 08:48, José María Valencia wrote:
> Ok, I understand your example, but before work with complex examples I want to "experiment" with a simple circuit as a simple DSB AM modulator based on the "theory" that I wrote in the past mail, I'm aware about realistic situations like noise and other factors and it was the reason I connected directly a wbx output to wbx input (different wbx) in the same usrp trying to avoid this realistic situations. > > Now I know that is necessary an attenuator (in this moment I don't have an attenuator) and I use two antennas, but I need to know if the usrp mathematically works like I'm believing…. I previously observed that direct connection between TX and RX has a *high* probability of damaging the LNA in the RX. Further, a direct connection will *not* remove all the noise. Analog electronics don't work that way. There is *always* noise in an electronic circuit at ordinary temperatures. 1/f noise, shot noise, various quantum effects. The only reason we don't have to think about that too much in the *digital* domain is that we quantize, so that there are voltage "zones" that represent 0s and 1s, and we choose those "zones" such that the various circuit noise "features" never (or almost never, statistically) cause us to make a wrong decision with respect to 1 and 0. In the analog domain, the noise matters and is always present.
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