Milos, FWIW WBX includes TX baseband filters of 40MHz bandwidth. LO offsetting your LO spur’s into those should suppress this. -Ian
> On Jan 3, 2019, at 3:48 AM, Milos Milosavljevic via USRP-users > <usrp-users@lists.ettus.com> wrote: > > Thank you Marcus. Much appreciated. > > I think I do understand why would I see some sort of phase noise if DUC > doesnt work but the only one bit of information that i am missing (i am sure > it is a silly question) is why would the offset be ignored if tune_request_t > is typcasted to float? Btw, just please note though that if a source is just > a constant (so basically there is no modulating signal) the spectrum is much > cleaner with float typcasting of tune_request then no typecasting. > > And lastly, since typecasting to float is no go, do you know how I can reduce > the spurs when i just use uhd.tune_request(f,lo_offset) without using > external filetring? I tried mode_n=integer but it doesnt help. Those spurs > are like 20MHz from the carrier and are destroying our amp (due to > reflections). 🙁 > > Thanks > Milos > > From: USRP-users <usrp-users-boun...@lists.ettus.com > <mailto:usrp-users-boun...@lists.ettus.com>> on behalf of Marcus D. Leech via > USRP-users <usrp-users@lists.ettus.com <mailto:usrp-users@lists.ettus.com>> > Sent: 03 January 2019 05:36 > To: usrp-users@lists.ettus.com <mailto:usrp-users@lists.ettus.com> > Subject: Re: [USRP-users] Unexpected spurious from N200 > > On 01/02/2019 08:06 PM, Milos Milosavljevic via USRP-users wrote: >> Dear All, >> >> I was wondering if somebody could clarify a couple of issues that I have >> with the UHD and N200 USRP. I am using the latest version of the software. >> >> I am generating a single tone to be transmitted with N200 (WBX board) using >> uhd_siggen as: >> >> uhd_siggen -g 15 -s 500000 -m 0.5 -f 402000000 --lo-offset 10000000 -x 50000 >> --sine >> >> 1) I can see quite a strong spurs at 10MHz and 20MHz freq offset from the >> carrier? (I am not using any external filtering) > Define "quite strong". > > >> >> 2) If I modify the siggen to use float((uhd.tune_request(f,lo_offset)) >> instead of just uhd.tune_request(f,lo_offset) the signal with constant >> source is much cleaner. However, if I modulate the carrier with a sine >> source another set of spurs appear very close to the carrier. This is not >> though the case when float is not used (but spurs at 10 and 20MHz are still >> present). >> >> Why does the float with tune_request make such a big difference? > Well, looks like you're casting a tune_request_t to a float, which means > that the offset instruction will likely get ignored, which changes > whether the DUC comes into play or not. > > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com <mailto:USRP-users@lists.ettus.com> > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com > <http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com>
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