On 01/04/2019 10:08 AM, Milos Milosavljevic wrote:
Hi Marcus,
> If you're driving an amplifier, it's *strongly* recommended to use a
filter anyway. That's just good RF plumbing practice regardless.
I agree. We didnt have filter out of convenience really but are
reconsidering it now.
For your questions:
(A) They are. Reducing the gain reduces relative magnitude of the spurs
(B) The strongest on at 20MHz from the carrier is 20 dBc (i.e.
relative to the carrier). At 40MHz about 20dBc. Others are about
45dBc. Same thing appears using either the single tone or a data
modulation like GMSK, etc. The lo_offset of 10MHz is used with
tune_request_t.
Please see in the attachment the output spectrum.
Many thanks,
Milos
Try reducing the magnitude of your modulation signal a little bit.
------------------------------------------------------------------------
*From:* Marcus D. Leech <patchvonbr...@gmail.com>
*Sent:* 03 January 2019 18:24
*To:* Milos Milosavljevic; Ian Buckley
*Cc:* usrp-users@lists.ettus.com
*Subject:* Re: [USRP-users] Unexpected spurious from N200
On 01/03/2019 12:53 PM, Milos Milosavljevic wrote:
No worries Ian. š Yeah I have tried different options with
tune_request object (including different lo_offsets) but not much
luck. There are a few quite strong spurs at 10,20 and some at higher
freq but nothing seems to help with reducing the power of those. It
looks like we would have to use a filter at the output of the USRP.
If anyone has any other ideas that would be much appreciated. If not
we will be putting filters which is a bit of a pain for us but if
thats the only option there is nothing we can do.
Thanks
Milos
If you're driving an amplifier, it's *strongly* recommended to use a
filter anyway. That's just good RF plumbing practice regardless.
Two questions:
(A) Are the spur *relative* magnitudes sensitive to RF gain setting?
(B) What are the relative magnitudes of the spurs?
------------------------------------------------------------------------
*From:* Ian Buckley <i...@ionconcepts.com> <mailto:i...@ionconcepts.com>
*Sent:* 03 January 2019 15:42
*To:* Milos Milosavljevic
*Cc:* usrp-users@lists.ettus.com <mailto:usrp-users@lists.ettus.com>;
Marcus D. Leech
*Subject:* Re: [USRP-users] Unexpected spurious from N200
Milos,
Early AM for meā¦.disregard what I just saidā¦had a pre-coffee
momentā¦LO not present in signal chain at that pointā¦doh!
On Jan 3, 2019, at 7:27 AM, Milos Milosavljevic
<milos_m...@hotmail.com <mailto:milos_m...@hotmail.com>> wrote:
Thank you Ian.
Apologies, we are using the SBX not WBX (that was a typo from my
side). I believe that SBX also has TX baseband filters.
Regardless, sorry, but what did you mean by offsetting the LO spur's
into those filters? Via tune_request_t?
Thanks
Milos
------------------------------------------------------------------------
*From:*Ian Buckley <i...@ionconcepts.com <mailto:i...@ionconcepts.com>>
*Sent:*03 January 2019 15:16
*To:*Milos Milosavljevic
*Cc:*usrp-users@lists.ettus.com <mailto:usrp-users@lists.ettus.com>;
Marcus D. Leech
*Subject:*Re: [USRP-users] Unexpected spurious from N200
Milos,
FWIW WBX includes TX baseband filters of 40MHz bandwidth. LO
offsetting your LO spurās into those should suppress this.
-Ian
On Jan 3, 2019, at 3:48 AM, Milos Milosavljevic via USRP-users
<usrp-users@lists.ettus.com <mailto: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).š
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.
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