[USRP-users] X310, 2 channel sample time and phase alignment

Marcus D. Leech mleech at ripnet.com
Tue Sep 2 14:12:32 EDT 2014


On 09/02/2014 01:57 PM, Kemp, Elizabeth - 1008 - MITLL wrote:
>
> Marcus -- The two channels are on two different BASIC_RX boards. I can 
> try updating to 3.7.2 and see if that changes anything.
>
> Ian -- Thanks, unfortunately I am using a 0 degree splitter (it would 
> be nice if that was the fix!). I also picked an example where they are 
> almost 180 degrees out of phase, for some other frequencies they are 
> actually pretty close. I am using a mini circuits ZX10-2-12-S+ 
> splitter -- according to the datasheet the phase unbalance should only 
> be 0.01 degrees at 50 MHz.
>
Is the phase offset always the same for any given frequency, or does it 
change from run to run?


> *From:*Ian Buckley [mailto:ianb at ionconcepts.com]
> *Sent:* Tuesday, September 02, 2014 1:37 PM
> *To:* Marcus D. Leech
> *Cc:* Kemp, Elizabeth - 1008 - MITLL; usrp-users at lists.ettus.com
> *Subject:* Re: [USRP-users] X310, 2 channel sample time and phase 
> alignment
>
> Thats a giant delay...nothing I can think of internal to X310 could 
> account for that. I don't suppose you accidentally used a 180 degree 
> splitter instead of a 0 degree? I only ask because I ddi the same once 
> and wasted a bunch of time...
>
> On Sep 2, 2014, at 10:28 AM, Marcus D. Leech via USRP-users 
> <usrp-users at lists.ettus.com <mailto:usrp-users at lists.ettus.com>> wrote:
>
>
>
> On 09/02/2014 01:25 PM, Kemp, Elizabeth - 1008 - MITLL wrote:
>
>     Thank you for the reply Marcus!
>
>     I just plotted as a complex pair and it still doesn't have the
>     proper phase alignment...  I'm using UHD version 3.7.1.
>
> Could you update to 3.7.2?
>
> Also, how are you setting up the two channels?  Are they on two 
> different BASIC_RX?
>
>
>
> -Liz
>
> *From:*USRP-users [mailto:usrp-users-bounces at lists.ettus.com] *On 
> Behalf Of *Marcus D. Leech via USRP-users
> *Sent:* Tuesday, September 02, 2014 11:49 AM
> *To:* usrp-users at lists.ettus.com <mailto:usrp-users at lists.ettus.com>
> *Subject:* Re: [USRP-users] X310, 2 channel sample time and phase 
> alignment
>
> On 09/02/2014 11:23 AM, Kemp, Elizabeth - 1008 - MITLL via USRP-users 
> wrote:
>
>     Hi,
>
>     I have a test set up where I am recording on both channels of an
>     X310.  I have the output of a signal generator connected to the
>     channels through a splitter (and equal length cables).  I am using
>     the BasicRX Daughterboards (1-250 MHz).
>
>     I have attached a screenshot from GRC of the WX GUI that shows a
>     plot of the real samples, and the magnitude of the two channels. 
>     As you can see in the magnitude plot, the two channels seem to be
>     time-aligned, but there is a huge phase offset between the two
>     channels.  I've observed that the phase offset varies across
>     different frequencies.
>
>     So my question is -- why is there a phase offset between the 2
>     channels?  Is there anything that can be done to correct it?
>
>     Thanks for your help,
>
>     Liz
>
>
>
>
>
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>
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>
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>
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>
> There may not be.  In the past, the scope sink has had issues with 
> proper phase display.  If you plot it as a complex pair instead, it 
> maintains proper phase
>   display.
>
> Also, what version of UHD are you using?
>
>
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