Hello, We are experiencing an issue with our UBX-160 when tuning to a sequence of center frequencies with  set_rx_frequency() and  set_tx_frequency() in which tuning to center frequencies in a particular order consistently results in significant degradation of the received signal. Sequence A: 100 MHz (default) —> 1000 MHz —> 500 MHz Sequence B: 100 MHz (default) —> 500 MHz —> 1000 MHz We are transmitting identical waveforms (non continuously, with prf of ~100 ms in external loopback with 30 dB attenuation) and estimate the PSD of the rx signal and apply a matched filter. With sequence A, the RX signal for both 1GHz and 500 MHz is ~4 dB weaker and has a noticeably attenuated/rounded spectrum in comparison to sequence B. The matched filter output is significantly degraded for sequence A. The issues seen with sequence A are repeatable and can be corrected at any time by tuning according to sequence B. I am guessing that this is caused by an issue in db_ubx.cpp. Is there a fix for this? We are on the rfnoc-devel branch of uhd and are up to date with commit 2cf80a6. Thank you, Sam

On 02/22/2017 03:26 PM, Samuel Prager via USRP-users wrote: > Hello, > > We are experiencing an issue with our UBX-160 when tuning to a > sequence of center frequencies with /set_rx_frequency()/ and > /set_tx_frequency()/ in which tuning to center frequencies in a > particular order consistently results in significant degradation of > the received signal. > > Sequence A: > 100 MHz (default) —> 1000 MHz —> 500 MHz > > Sequence B: > 100 MHz (default) —> 500 MHz —> 1000 MHz > > We are transmitting identical waveforms (non continuously, with prf of > ~100 ms in external loopback with 30 dB attenuation) and estimate the > PSD of the rx signal and apply a matched filter. > > With sequence A, the RX signal for both 1GHz and 500 MHz is ~4 dB > weaker and has a noticeably attenuated/rounded spectrum in comparison > to sequence B. The matched filter output is significantly degraded for > sequence A. The issues seen with sequence A are repeatable and can be > corrected at any time by tuning according to sequence B. > > I am guessing that this is caused by an issue in db_ubx.cpp. Is there > a fix for this? We are on the rfnoc-devel branch of uhd and are up to > date with commit 2cf80a6. > > Thank you, > > Sam > > > The analog signal chain is slightly different above 500MHz. Internally, the UBX is a superhet implementation, and there's a switch of IF schemes and analog bits and pieces (amplifiers, etc) at 500Mhz, from what I recall. In sequence (B), you're likely staying with one set of hardware until you go to 1000MHz, and with sequence (A) you're switching twice.