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> on behalf of Marcus D. Leech via USRP-users <usrp-users@lists.ettus.com> Sent: 03 January 2019 05:36 To: 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.
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