Got it. Thanks very much, Marcus! I didn’t realize that the LO was a square wave going in.
Thanks for the info and the tips about moving forward! From: Marcus D. Leech <patchvonbr...@gmail.com> Sent: Monday, April 17, 2023 8:02 PM To: Shenk, Trey E <trey.sh...@pnnl.gov> Cc: USRP-users@lists.ettus.com Subject: Re: [USRP-users] Harmonic Distortion with B205mini On 17/04/2023 22:49, Shenk, Trey E wrote: Hi all, Thanks for the input on this issue. I’m still trying to pin it down. I’m using gnuradio to drive a B205mini. I’m seeing harmonics of the carrier particularly at odd harmonics. The third harmonic, 3*carrier, is only 10dB down from the carrier itself, and I’m seeing significant carrier leakage. I’ve tried changing the sampling rate, as well as modulating a QPSK signal (both direct conversion and using some off-tuning). I still see spectral images at the odd harmonics. Is this known behavior for the B205mini? I’m trying to decide if I need to change how I’m driving it, use a RF filter at the output, or switch to a different SDR. Thanks, Trey Two things. The LO leakage can be dealt with using an LO offset. However, the AD9361 uses a square-wave LO into the mixer, which means that odd harmonics will make it out of the device. This has been discussed extensively in the ADI forums, and a couple of folks on this list have discussed it as well with spectrum analyzer screen dumps showing it. I confirmed it with my own modest spectrum analyzer as well. Because it's an odd-harmonic problem, any application operating above 2GHz will naturally not have this problem, because the 3rd harmonic (and all other odd harmonics) will fall outside the operating range of the AD9361 chip. The only solution is filtering. Some USRPs have a built-in switchable filter bank that can help with this in some cases, but it really depends on the frequency scheme of your application. A discrete filter bank cannot possibly deal with all applications. I personally tend to think of SDRs as *components* in an overall engineered RF *system*. It is certainly the case that ready-for-type-acceptance radios, regardless of internal architecture, will almost always have filters at the edges to deal with architectural unpleasantness deeper in the radio architecture. The B2xx series were designed to be relatively inexpensive, and as such, they don't have a switchable filter-bank on them--and as previously pointed out, even THEN, that may not necessarily make the radio "application ready" in terms of formal type-acceptance, etc. From: Shenk, Trey E Sent: Wednesday, April 12, 2023 4:21 PM To: Marcus D. Leech <patchvonbr...@gmail.com><mailto:patchvonbr...@gmail.com> Cc: USRP-users@lists.ettus.com<mailto:USRP-users@lists.ettus.com> Subject: RE: [USRP-users] Harmonic Distortion with B205mini 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<mailto:patchvonbr...@gmail.com>> Sent: Monday, April 10, 2023 10:22 PM To: Shenk, Trey E <trey.sh...@pnnl.gov<mailto:trey.sh...@pnnl.gov>> Cc: USRP-users@lists.ettus.com<mailto: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><mailto:patchvonbr...@gmail.com> Sent: Monday, April 10, 2023 8:39 AM To: Shenk, Trey E <trey.sh...@pnnl.gov><mailto:trey.sh...@pnnl.gov> Cc: USRP-users@lists.ettus.com<mailto: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<mailto: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<mailto:usrp-users@lists.ettus.com> To unsubscribe send an email to usrp-users-le...@lists.ettus.com<mailto: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
