[USRP-users] Improving Sensitivity of the Radio.

Kyeong Su Shin ksshin at uw.edu
Tue Nov 14 22:40:45 EST 2017


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 <mleech at 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 at 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 at 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.
>>
>>
>>
>>
>>
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>> USRP-users at lists.ettus.com
>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
>>
>>
>
>
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