Hello, This might be a common effect but I don't comprehend why it happens and if it is avoidable. I'm using a N210+CBX to transmit a 10 MSPS OFDM signal, with Fc = 1.5 GHz. When transmitting, I can see some kind of "replicas" at +-7.5 MHz from Fc, always with a 40 dBc difference. $ sudo /lib/uhd/examples/tx_samples_from_file --freq 1500e6 --rate 10e6 --gain 20 --type float --file ~/OFDMsignal.raw --args="name=sdr1" [cid:84936214-4fd6-43b7-826b-c47101223b50] I've already tried changing lo_offset and executing the calibration utilities for IQ imbalance, but none of that seems related to the problem. Could anyone provide any insight? Regards.

Those are aliases. Try setting the analog bandwidth with the --bw parameter. Ron On 7/17/24 03:58, Brais Ares Fernández wrote: > Hello, > > This might be a common effect but I don't comprehend why it happens > and if it is avoidable. > > I'm using a N210+CBX to transmit a 10 MSPS *OFDM signal*, with Fc = > 1.5 GHz. When transmitting, I can see some kind of "replicas" at +-7.5 > MHz from Fc, always with a 40 dBc difference. > > $ sudo /lib/uhd/examples/tx_samples_from_file --freq 1500e6 --rate > 10e6 --gain 20 --type float --file ~/OFDMsignal.raw --args="name=sdr1" > > > I've already tried changing lo_offset and executing the calibration > utilities for IQ imbalance, but none of that seems related to the problem. > > Could anyone provide any insight? > > Regards. >

Hello, Ron. Thank you for the answer. I've already tried but it seems to do nothing: $ sudo /lib/uhd/examples/tx_samples_from_file --freq 1500e6 --rate 10e6 --gain 20 --bw 10e6 --type float --file ~/OFDMsignal.raw --args="name=sdr1" I even tried weird values like 100e3 or 100e6, but no apparent effect over the spectrum at all. ________________________________ De: Ron Economos via USRP-users <usrp-users@lists.ettus.com> Enviado: miércoles, 17 de julio de 2024 15:00 Para: usrp-users@lists.ettus.com <usrp-users@lists.ettus.com> Asunto: [USRP-users] Re: Replicas out of band in OFDM signal (N210+CBX) Those are aliases. Try setting the analog bandwidth with the --bw parameter. Ron On 7/17/24 03:58, Brais Ares Fernández wrote: Hello, This might be a common effect but I don't comprehend why it happens and if it is avoidable. I'm using a N210+CBX to transmit a 10 MSPS OFDM signal, with Fc = 1.5 GHz. When transmitting, I can see some kind of "replicas" at +-7.5 MHz from Fc, always with a 40 dBc difference. $ sudo /lib/uhd/examples/tx_samples_from_file --freq 1500e6 --rate 10e6 --gain 20 --type float --file ~/OFDMsignal.raw --args="name=sdr1" [cid:part1.OrFBfEJE.b5MD2DaO@comcast.net] I've already tried changing lo_offset and executing the calibration utilities for IQ imbalance, but none of that seems related to the problem. Could anyone provide any insight? Regards.

Yeah, I think UHD sets it to some calculated value that can't be overwritten. BTW, here's what the spectrum looks like with a very wide analog filter. So the default bandwidth setting on the N210/CBX is just a little too wide to fully suppress that first alias. OFDM alias Ron On 7/17/24 06:39, Brais Ares Fernández wrote: > Hello, Ron. Thank you for the answer. > > I've already tried but it seems to do nothing: > > $ sudo /lib/uhd/examples/tx_samples_from_file --freq 1500e6 --rate > 10e6 --gain 20 *--bw 10e6* --type float --file ~/OFDMsignal.raw > --args="name=sdr1" > > I even tried weird values like 100e3 or 100e6, but no apparent effect > over the spectrum at all. > ------------------------------------------------------------------------ > *De:* Ron Economos via USRP-users <usrp-users@lists.ettus.com> > *Enviado:* miércoles, 17 de julio de 2024 15:00 > *Para:* usrp-users@lists.ettus.com <usrp-users@lists.ettus.com> > *Asunto:* [USRP-users] Re: Replicas out of band in OFDM signal (N210+CBX) > > Those are aliases. Try setting the analog bandwidth with the --bw > parameter. > > > Ron > > > On 7/17/24 03:58, Brais Ares Fernández wrote: >> Hello, >> >> This might be a common effect but I don't comprehend why it happens >> and if it is avoidable. >> >> I'm using a N210+CBX to transmit a 10 MSPS *OFDM signal*, with Fc = >> 1.5 GHz. When transmitting, I can see some kind of "replicas" at >> +-7.5 MHz from Fc, always with a 40 dBc difference. >> >> $ sudo /lib/uhd/examples/tx_samples_from_file --freq 1500e6 --rate >> 10e6 --gain 20 --type float --file ~/OFDMsignal.raw --args="name=sdr1" >> >> >> I've already tried changing lo_offset and executing the calibration >> utilities for IQ imbalance, but none of that seems related to the >> problem. >> >> Could anyone provide any insight? >> >> Regards. >>

On 17/07/2024 09:39, Brais Ares Fernández wrote: > Hello, Ron. Thank you for the answer. > > I've already tried but it seems to do nothing: > > $ sudo /lib/uhd/examples/tx_samples_from_file --freq 1500e6 --rate > 10e6 --gain 20 *--bw 10e6* --type float --file ~/OFDMsignal.raw > --args="name=sdr1" > > I even tried weird values like 100e3 or 100e6, but no apparent effect > over the spectrum at all. The CBX doesn't support variable analog bandwidth. Is your signal file actually sampled at 10e6 SPS? What happens if you reduce the sample magnitude on your input file to something like 0.8 and re-try? Are you certain that the input signal doesn't already have these artifacts in it?

On 17/07/2024 10:05, Ron Economos via USRP-users wrote: > > Yeah, I think UHD sets it to some calculated value that can't be > overwritten. > Many daughtercards for USRP platforms that take daughtercards have fixed analog bandwidth. On the CBX, there's a balanced elliptical filter giving 40MHz of analog bandwidth. > > BTW, here's what the spectrum looks like with a very wide analog > filter. So the default bandwidth setting on the N210/CBX is just a > little too wide to fully suppress that first alias. > > > OFDM alias > > > Ron > > > On 7/17/24 06:39, Brais Ares Fernández wrote: >> Hello, Ron. Thank you for the answer. >> >> I've already tried but it seems to do nothing: >> >> $ sudo /lib/uhd/examples/tx_samples_from_file --freq 1500e6 --rate >> 10e6 --gain 20 *--bw 10e6* --type float --file ~/OFDMsignal.raw >> --args="name=sdr1" >> >> I even tried weird values like 100e3 or 100e6, but no apparent effect >> over the spectrum at all. >> ------------------------------------------------------------------------ >> *De:* Ron Economos via USRP-users <usrp-users@lists.ettus.com> >> *Enviado:* miércoles, 17 de julio de 2024 15:00 >> *Para:* usrp-users@lists.ettus.com <usrp-users@lists.ettus.com> >> *Asunto:* [USRP-users] Re: Replicas out of band in OFDM signal >> (N210+CBX) >> >> Those are aliases. Try setting the analog bandwidth with the --bw >> parameter. >> >> >> Ron >> >> >> On 7/17/24 03:58, Brais Ares Fernández wrote: >>> Hello, >>> >>> This might be a common effect but I don't comprehend why it happens >>> and if it is avoidable. >>> >>> I'm using a N210+CBX to transmit a 10 MSPS *OFDM signal*, with Fc = >>> 1.5 GHz. When transmitting, I can see some kind of "replicas" at >>> +-7.5 MHz from Fc, always with a 40 dBc difference. >>> >>> $ sudo /lib/uhd/examples/tx_samples_from_file --freq 1500e6 --rate >>> 10e6 --gain 20 --type float --file ~/OFDMsignal.raw --args="name=sdr1" >>> >>> >>> I've already tried changing lo_offset and executing the calibration >>> utilities for IQ imbalance, but none of that seems related to the >>> problem. >>> >>> Could anyone provide any insight? >>> >>> Regards. >>> > > _______________________________________________ > USRP-users mailing list --usrp-users@lists.ettus.com > To unsubscribe send an email tousrp-users-leave@lists.ettus.com

The alias filter is at baseband. It would be on the N210 Ron On 7/17/24 08:11, Marcus D. Leech wrote: > On 17/07/2024 10:05, Ron Economos via USRP-users wrote: >> >> Yeah, I think UHD sets it to some calculated value that can't be >> overwritten. >> > Many daughtercards for USRP platforms that take daughtercards have > fixed analog bandwidth. > > On the CBX, there's a balanced elliptical filter giving 40MHz of > analog bandwidth. > > >> >> BTW, here's what the spectrum looks like with a very wide analog >> filter. So the default bandwidth setting on the N210/CBX is just a >> little too wide to fully suppress that first alias. >> >> >> OFDM alias >> >> >> Ron >> >> >> On 7/17/24 06:39, Brais Ares Fernández wrote: >>> Hello, Ron. Thank you for the answer. >>> >>> I've already tried but it seems to do nothing: >>> >>> $ sudo /lib/uhd/examples/tx_samples_from_file --freq 1500e6 --rate >>> 10e6 --gain 20 *--bw 10e6* --type float --file ~/OFDMsignal.raw >>> --args="name=sdr1" >>> >>> I even tried weird values like 100e3 or 100e6, but no apparent >>> effect over the spectrum at all. >>> ------------------------------------------------------------------------ >>> *De:* Ron Economos via USRP-users <usrp-users@lists.ettus.com> >>> *Enviado:* miércoles, 17 de julio de 2024 15:00 >>> *Para:* usrp-users@lists.ettus.com <usrp-users@lists.ettus.com> >>> *Asunto:* [USRP-users] Re: Replicas out of band in OFDM signal >>> (N210+CBX) >>> >>> Those are aliases. Try setting the analog bandwidth with the --bw >>> parameter. >>> >>> >>> Ron >>> >>> >>> On 7/17/24 03:58, Brais Ares Fernández wrote: >>>> Hello, >>>> >>>> This might be a common effect but I don't comprehend why it happens >>>> and if it is avoidable. >>>> >>>> I'm using a N210+CBX to transmit a 10 MSPS *OFDM signal*, with Fc = >>>> 1.5 GHz. When transmitting, I can see some kind of "replicas" at >>>> +-7.5 MHz from Fc, always with a 40 dBc difference. >>>> >>>> $ sudo /lib/uhd/examples/tx_samples_from_file --freq 1500e6 --rate >>>> 10e6 --gain 20 --type float --file ~/OFDMsignal.raw --args="name=sdr1" >>>> >>>> >>>> I've already tried changing lo_offset and executing the calibration >>>> utilities for IQ imbalance, but none of that seems related to the >>>> problem. >>>> >>>> Could anyone provide any insight? >>>> >>>> Regards. >>>> >> >> _______________________________________________ >> USRP-users mailing list --usrp-users@lists.ettus.com >> To unsubscribe send an email tousrp-users-leave@lists.ettus.com > > > _______________________________________________ > USRP-users mailing list --usrp-users@lists.ettus.com > To unsubscribe send an email tousrp-users-leave@lists.ettus.com

On 17/07/2024 11:50, Ron Economos via USRP-users wrote: > > The alias filter is at baseband. It would be on the N210 > The mixer is on the daughtercard.   The analog filters are between the DAC/ADC (on the motherboard), and   the mixers on the daughtercard. The filters on the motherboard are DSP based--to effect DUC/DDC mechanisms. Page 5, here: https://files.ettus.com/schematics/cbx/CBX.pdf The N210 relies on the daughterboards to provide analog anti-aliasing -- schematics for N210 motherboard are here: https://files.ettus.com/schematics/n200/n2xx.pdf > > Ron > > > On 7/17/24 08:11, Marcus D. Leech wrote: >> On 17/07/2024 10:05, Ron Economos via USRP-users wrote: >>> >>> Yeah, I think UHD sets it to some calculated value that can't be >>> overwritten. >>> >> Many daughtercards for USRP platforms that take daughtercards have >> fixed analog bandwidth. >> >> On the CBX, there's a balanced elliptical filter giving 40MHz of >> analog bandwidth. >> >> >>> >>> BTW, here's what the spectrum looks like with a very wide analog >>> filter. So the default bandwidth setting on the N210/CBX is just a >>> little too wide to fully suppress that first alias. >>> >>> >>> OFDM alias >>> >>> >>> Ron >>> >>> >>> On 7/17/24 06:39, Brais Ares Fernández wrote: >>>> Hello, Ron. Thank you for the answer. >>>> >>>> I've already tried but it seems to do nothing: >>>> >>>> $ sudo /lib/uhd/examples/tx_samples_from_file --freq 1500e6 --rate >>>> 10e6 --gain 20 *--bw 10e6* --type float --file ~/OFDMsignal.raw >>>> --args="name=sdr1" >>>> >>>> I even tried weird values like 100e3 or 100e6, but no apparent >>>> effect over the spectrum at all. >>>> ------------------------------------------------------------------------ >>>> *De:* Ron Economos via USRP-users <usrp-users@lists.ettus.com> >>>> *Enviado:* miércoles, 17 de julio de 2024 15:00 >>>> *Para:* usrp-users@lists.ettus.com <usrp-users@lists.ettus.com> >>>> *Asunto:* [USRP-users] Re: Replicas out of band in OFDM signal >>>> (N210+CBX) >>>> >>>> Those are aliases. Try setting the analog bandwidth with the --bw >>>> parameter. >>>> >>>> >>>> Ron >>>> >>>> >>>> On 7/17/24 03:58, Brais Ares Fernández wrote: >>>>> Hello, >>>>> >>>>> This might be a common effect but I don't comprehend why it >>>>> happens and if it is avoidable. >>>>> >>>>> I'm using a N210+CBX to transmit a 10 MSPS *OFDM signal*, with Fc >>>>> = 1.5 GHz. When transmitting, I can see some kind of "replicas" at >>>>> +-7.5 MHz from Fc, always with a 40 dBc difference. >>>>> >>>>> $ sudo /lib/uhd/examples/tx_samples_from_file --freq 1500e6 --rate >>>>> 10e6 --gain 20 --type float --file ~/OFDMsignal.raw --args="name=sdr1" >>>>> >>>>> >>>>> I've already tried changing lo_offset and executing the >>>>> calibration utilities for IQ imbalance, but none of that seems >>>>> related to the problem. >>>>> >>>>> Could anyone provide any insight? >>>>> >>>>> Regards. >>>>> >>> >>> _______________________________________________ >>> USRP-users mailing list --usrp-users@lists.ettus.com >>> To unsubscribe send an email tousrp-users-leave@lists.ettus.com >> >> >> _______________________________________________ >> USRP-users mailing list --usrp-users@lists.ettus.com >> To unsubscribe send an email tousrp-users-leave@lists.ettus.com > > _______________________________________________ > USRP-users mailing list --usrp-users@lists.ettus.com > To unsubscribe send an email tousrp-users-leave@lists.ettus.com