Hi Marcus,
Yeah I tried that as well. It doesnt help much. Btw apologies if you received
two copies of this email. I tried sending it from my phone but I dont think it
got sent for some reason.
I saw one of your posts here on a different topic and meant to ask, only if you
have a spare few mins sometimes if not no worries, to try to reproduce what I
see on N310 or x310 (since I saw that you have those) using for example the
siggen the way I was using it (as given in of my responses below)? I am just
curious to see whether I am doing something fundamentally wrong or this is
specific to N200.
Anyway, only if you have time and/or resources. If not never mind we will go
with the filter at the output as it seems that nothing I do helps with
suppressing these spurs with N200 and SBX.
Thanks
Milos
________________________________
From: Marcus D. Leech <patchvonbr...@gmail.com>
Sent: 04 January 2019 18:55
To: Milos Milosavljevic
Cc: usrp-users@lists.ettus.com
Subject: Re: [USRP-users] Unexpected spurious from N200
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><mailto:patchvonbr...@gmail.com>
Sent: 03 January 2019 18:24
To: Milos Milosavljevic; Ian Buckley
Cc: usrp-users@lists.ettus.com<mailto: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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