You've seen the filters from Pole-Zero, right? Tunable, but very narrow BW. I keep reading abstracts in IEEE journals but I haven't seen anything interesting. Sub-octave band counts add up fast :-(
Dave On Sun, Apr 16, 2023 at 9:36 PM Marcus D. Leech <patchvonbr...@gmail.com> wrote: > On 16/04/2023 21:13, David Bengtson wrote: > > Yes, it's pretty typical that the output of an SDR needs additional > filtering and gain on the transmit side, and similarly filters and gain on > the receive side. I spent a substantial fraction of my time at a previous > job designing application specific front ends for Ettus SDR's. > > Dave > > > In my other job, I do radio astronomy. "Filter early, filter often" is > what gets the job done in that domain. A many-octave > tunable filter with variable bandwidth would be a nice thing, except for > the ongoing miners strike at the > unobtanium mines... > > > On Wed, Apr 12, 2023 at 8:39 PM Marcus D. Leech <patchvonbr...@gmail.com> > wrote: > >> On 12/04/2023 20:28, Ron Economos wrote: >> >> This is what I see with a B210 at 145 MHz fundamental. I had the analyzer >> on a large RBW, so the even order harmonic are buried in the analyzer noise. >> >> I don't think there's any remedy except for external filters. >> >> Ron >> [image: B210 harmonics] >> >> Thanks Ron. That looks like what my TinySA produced for 250Mhz carrier. >> I need to learn more about it so that I can >> record spectra with it. There's a Linux app for it that I need to >> explore.... >> >> >> Anyway, the basic issue, having consulted some older Analog Devices forum >> posts is that the LO produces a square-wave >> signal, which means that all the odd-order harmonics will be present in >> it, and naturally, mix with the baseband. >> There's nothing that can be done other than, as you point out, filter. >> As you move up in frequency, this becomes >> very much easier of course, and at 2GHz, the 3rd harmonic is outside >> the supported passband of the AD9361, and >> you won't see it. >> >> I didn't realize this about the AD9361 chip, and other Ettus devices have >> automatically switchable filters that can >> (often, not always) remediate this issue. The E3xx series, the N3xx >> series, the TwinRX cards for the X310 and friends. >> >> But I'll point out again that "built for purpose" radios nearly-always >> have output (input) filtering to reduce or eliminate >> unintended consequences of architecture choices deeper within the >> radio. Since SDRs in general don't get to be >> "built for purpose" either ever, or until some specific application is >> using them as their "radio bits", it's hard to come up >> with a universal RF filtering scheme that is suitable for all >> applications. >> >> I'd never noticed this issue because I don't really ever TX in my "day >> job" use of these devices (radio astronomy), and on >> the RX side, I always pre-filter anyway, usually rather aggressively. >> >> >> On 4/12/23 16:20, Shenk, Trey E via USRP-users wrote: >> >> The original signal that I showed was an unmodulated carrier. >> >> I tried a 10kHz complex exponential (plots included for several >> harmonics). The carrier is clearly visible at all frequencies. I can see >> copies of the 10kHz tone on odd multiples of the carrier, but not on the >> even multiples. >> >> >> >> >> >> >> >> *From:* Marcus D. Leech <patchvonbr...@gmail.com> >> <patchvonbr...@gmail.com> >> *Sent:* Monday, April 10, 2023 10:22 PM >> *To:* Shenk, Trey E <trey.sh...@pnnl.gov> <trey.sh...@pnnl.gov> >> *Cc:* USRP-users@lists.ettus.com >> *Subject:* Re: [USRP-users] Harmonic Distortion with B205mini >> >> >> >> On 10/04/2023 14:28, Shenk, Trey E wrote: >> >> I first tried turning the gain down. What I saw was that the even >> harmonics (2*fundamental, …) did not change power, and the odd harmonics >> decreased by the same amount as the fundamental. This means that the dBc >> for the odd harmonics stayed the same with decreasing gain. >> >> >> >> Decreasing the baseband amplitude had the exact same effect. Even >> harmonics stayed at the same power level, odd harmonics decreased while >> maintaining dBc. >> >> What is the nature of the modulating signal? >> >> If you use an example app like "tx_waveforms" with, let's say, 10kHz SIN >> signal, what are the harmonic results? >> >> >> >> >> >> >> >> *From:* Marcus D Leech <patchvonbr...@gmail.com> >> <patchvonbr...@gmail.com> >> *Sent:* Monday, April 10, 2023 8:39 AM >> *To:* Shenk, Trey E <trey.sh...@pnnl.gov> <trey.sh...@pnnl.gov> >> *Cc:* USRP-users@lists.ettus.com >> *Subject:* Re: [USRP-users] Harmonic Distortion with B205mini >> >> >> >> Check twice before you click! This email originated from outside PNNL. >> >> >> >> Turn down the RF gain a bit as well as the baseband amplitude. Does this >> make any difference? >> >> >> >> >> >> Sent from my iPhone >> >> >> >> >> On Apr 10, 2023, at 9:41 AM, Shenk, Trey E via USRP-users < >> usrp-users@lists.ettus.com> wrote: >> >> >> >> I'm using a B205mini to transmit signals. When transmitting, I can see >> copies of the SOI at harmonics of the center frequency. I ran some >> measurements of total harmonic distortion, and found it to range from 39% >> with a 100MHz to 23% with a 1GHz carrier. The second harmonic is <-50dBc, >> but the third harmonic is usually around -10dBc. >> >> My main concern is for the lower frequency carriers, like 100MHz, because >> multiple harmonics will show up on a spectrum analyzer set to a wideband. >> I've looked at putting an RF filter at the output, but I need the system to >> be able to switch transmit center frequencies in a range from 100MHz to >> 5GHz. >> >> Is it possible to reduce the harmonics by some hardware setting (driving >> with gnruadio)? >> >> Thanks, >> Trey >> >> >> >> <carrier_freqsweep_fc0200M_gain55.png> >> >> _______________________________________________ >> USRP-users mailing list -- usrp-users@lists.ettus.com >> To unsubscribe send an email to usrp-users-le...@lists.ettus.com >> >> >> >> _______________________________________________ >> USRP-users mailing list -- usrp-users@lists.ettus.com >> To unsubscribe send an email to usrp-users-le...@lists.ettus.com >> >> >> _______________________________________________ >> USRP-users mailing list -- usrp-users@lists.ettus.com >> To unsubscribe send an email to usrp-users-le...@lists.ettus.com >> >> >> _______________________________________________ >> USRP-users mailing list -- usrp-users@lists.ettus.com >> To unsubscribe send an email to usrp-users-le...@lists.ettus.com >> > >
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