Hi Matis, The USRPs are generally designed following the rule of thumb that the passband is 80% of sampling rate. That allows for filters, both analog and digital, to be reasonable to construct. The TwinRX is tuning its analog center frequency to 50 MHz. With the 100 MS/s complex sample rate frequencies from DC to 100 MHz are visible, but the filters, amplifiers, and other elements of the receiver will degrade the receive performance below 10 MHz. As you've found though, the degradation is very acceptable for some applications.
Marcus actually authored an app note looking at the same question with the UBX daughterboard. https://kb.ettus.com/Experiments_with_the_UBX_Daughterboard_in_the_HF_Band Regards, Derek On Sat, Mar 24, 2018 at 6:15 AM, Matis Alun via USRP-users < usrp-users@lists.ettus.com> wrote: > yes, its seems that we loose several dBs but which can be widely > compensated by the > extremely large TwinRx gain range. > > > Le 24/03/2018 à 06:38, Marcus D. Leech via USRP-users a écrit : > > On 03/24/2018 12:41 AM, Matis Alun via USRP-users wrote: > >> Hi, > >> > >> The TwinRx frequency specifications is from 10MHz to 6GHz. > >> > >> However, some tests shows that I can select the center frequency around > 10 MHz with a > >> sampling frequency of 25MHz > >> which allows to make some acquisitions in the HF band (3-30 MHz) with a > very good quality. > >> > >> My question is: why the specs limits to 10 MHz ? Is the RF part have > degraded performances > >> under this frequency ? > >> > >> Below this question is: we have to deliver a big HF (3-30 MHz) system > to a customer. The > >> acquisition part is actually built with > >> 2 x N210 with LFRX daughter boards. Due to the lack of chain gain of > this configuration, > >> we add some RF pre-amplifiers > >> in order to have good RF levels at the LFRX input. > >> Maybe that this configuration can be replaced by 1x X300 + TwinRx (we > didn't make this > >> choice because of the TwinRx specs) ? > >> > >> Regards, > >> > >> matis > >> > >> > > My guess is that signals below 10MHz can be received, but the RF > amplifiers in the > > low-band portion of the TwinRx likely fall off in gain quite a bit > > below 10MHz. > > > > > > > > _______________________________________________ > > USRP-users mailing list > > USRP-users@lists.ettus.com > > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com > > > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >
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