Dear Marcus D. Leech: Thank you very much! I will think about this.
Regards, Kyeong Su Shin On Tue, Nov 14, 2017 at 7:37 PM, Marcus D. Leech <mle...@ripnet.com> wrote: > On 11/14/2017 10:31 PM, Kyeong Su Shin wrote: > > Dear Marcus D. Leech: > > Thank you for the reply. > > Is the only advantage of the TwinRX the pre-selector filter bank? Or, can > the superheterodyne design of the radio also affect the data quality in > some ways? > > A Low-IF superhet design has some advantages, but the UBX has the same > overall architecture. With a Zero-iF design, mixer balance is extremely > important, and not always easy to achieve "perfectly". In the end, it's > a matter of where your mixer images end up. > > > We do turn down the gain to get optimal results. (The 'noise figure' that > I mentioned was the noise figure that is observed by us, after such > adjustments). We will definitely try adding filters. > > Keep in mind that filters "out front" necessarily add to the noise figure > of your receiver, since they aren't loss-free. RF system design is all > about > trade-offs. > > > > > Regards, > Kyeong Su Shin > > On Tue, Nov 14, 2017 at 7:12 PM, Marcus D. Leech via USRP-users < > usrp-users@lists.ettus.com> wrote: > >> On 11/14/2017 10:00 PM, Kyeong Su Shin via USRP-users wrote: >> >> Hello Everyone: >> >> We are using USRPs for spectrum sensing (on pretty much any frequencies). >> Before asking my faculty to order a TwinRX daughterboard, however, I would >> like to see if there are any ways to improve the sensitivity of the >> hardware that we currently own (UBX/SBX/CBX/WBX). >> >> Our USRP + UBX configuration works well, except that we cannot really >> increase the gain level much without putting the RF frontend into the >> nonlinear region. Because of this, the noise figure of our data is about >> ~30dB in the worst case. I believe that the main problem is that we are >> using a wideband outdoor discone antenna for this - dumping quite a lot of >> RF energy to the RF frontend. >> >> In this case, what could I try to improve the sensitivity of the radio? I >> think one option could be adding additional filters to the chain (when we >> know that we are only looking at a certain frequencies), but I wonder if >> there are anything else that I can try. >> >> Also, I wonder what differences we can expect if we switch our >> daughterboard to a TwinRX. Would it be worth it? What noise figures did >> people experience when a wideband outdoor antenna was connected to the >> board? >> >> Regards, >> Kyeong Su Shin >> >> >> _______________________________________________ >> USRP-users mailing >> listUSRP-users@lists.ettus.comhttp://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >> >> In the case of overload, the noise-figure is NOT the dominating factor in >> determining system sensitivity. >> >> If you are "sensing" across a limited band, then a filter that covers >> that band, and that band only, will definitely help keep the very first >> gain stages, >> which are "wide open" from going into overload. >> >> The TwinRX has some significant advantage here, since it has pre-selector >> filters, but those filters may or may not have band edges that correspond >> adequately to the band that your are "sensing". >> >> Basically, there's a "tension" in small-signal RF amplifiers. They can >> either have very high dynamic range, or they can have very-low noise figure. >> That general axiom still applies, although things are getting somewhat >> better in this regard. But taking the output of an outdoor disc-cone >> antenna >> in a normal urban environment is pretty-much begging for >> non-linearity. You might try turning *down* the gain. >> >> >> >> >> >> _______________________________________________ >> USRP-users mailing list >> USRP-users@lists.ettus.com >> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >> >> > >
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