[USRP-users] Master Clock Supression

Marcus D. Leech mleech at ripnet.com
Fri Jul 17 17:16:10 EDT 2015


On 07/17/2015 03:45 PM, devin kelly via USRP-users wrote:
> I'm not sure what you mean by offset tuning.  Is that like just tuning 
> to avoid the tone? Or, is it like the tone might have less power at 
> different frequencies I tune to (like tuning to 3.0505 GHz might give 
> me a lower tone-power than 3.5 GHz)?
>
> Devin
http://files.ettus.com/manual/page_general.html#general_tuning_process

>
> On Fri, Jul 17, 2015 at 3:15 PM, <mleech at ripnet.com 
> <mailto:mleech at ripnet.com>> wrote:
>
>     Try with offset tuning.  If they're still there, then they are
>     probably actual clock spurs, rather than enhanced LO
>      leakage.
>
>     On 2015-07-17 15:04, devin kelly via USRP-users wrote:
>
>>     Right now I've got two X310s each with two UBXs.  I have each
>>     TX/RX antenna on subdev A connected to each other (with 40 dB of
>>     attenuation), same for each B subdev.  I have all the RX2
>>     antennas terminated.
>>     I see the tones on regardless of the subdev/antenna combination. 
>>     I also tried connecting a spectrum analyzer to the TX/RX antenna
>>     ports and saw no tones.  I also put an antenna on my spectrum
>>     analyzer and saw no tones over the air with the antenna right
>>     next to each X310.
>>     Thanks Again,
>>     Devin
>>
>>     On Fri, Jul 17, 2015 at 11:19 AM, Marcus Müller
>>     <usrp-users at lists.ettus.com <mailto:usrp-users at lists.ettus.com>>
>>     wrote:
>>
>>         Shielding/separation-wise, the X310 should be pretty much
>>         superior in every aspect -- not only is the ADC, DAC, mixer,
>>         amplifier and LO synthesizers in one package on the B2x0 (the
>>         AD9361); the X310 is modular in the sense that the MCR
>>         doesn't even appear to the daugtherboards, necessarily; it's
>>         an FPGA-only clock, generated by the clock distribution IC on
>>         the mainboard, and the UBX, especially to suppress strong
>>         interferers, has a metal can (which is unique among our RF
>>         hardware, so far). Under that metal can, there's a lot of
>>         partitions, which align with the different jobs and frequency
>>         ranges on the board, compare the schematic [1].
>>
>>         So since you're seeing 200MHz-harmonics, these might either
>>         spuriously get into the antenna ports, or for some reason, at
>>         multiples of 200MHz LO leakage is worse (I don't expect
>>         that). Have you tried using offset tuning [2] to reduce these
>>         spurs?
>>
>>         Best regards,
>>         Marcus
>>
>>
>>         [1] http://files.ettus.com/schematics/ubx/ubx.pdf
>>         [2]
>>         http://files.ettus.com/manual/page_general.html#general_tuning_process
>>
>>
>>
>>         On 17.07.2015 17:03, devin kelly via USRP-users wrote:
>>>         Hello,
>>>         I have an X310 with a UBX daughtercard.  I've noticed that
>>>         there are tones every 200 MHz (I checked 2.4GHx, 2.6 GHz,
>>>         2.8 GHz, 3 GHz, 3.2 GHz).  Do I have any options for
>>>         suppressing the tones?  Is there any shielding or RF
>>>         absorber I can add somewhere?
>>>         The B210s seem to have each section of radio gated off (to
>>>         make it easier to add shielding?).  But  the X310s don't as
>>>         far as I can tell.
>>>         Thanks for any help,
>>>         Devin
>>>
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>>>         http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
>>
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>>
>>
>>     -- 
>>     http://alum.wpi.edu/~dkelly/ <http://alum.wpi.edu/%7Edkelly/>
>>
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>
>
>
>
> -- 
> http://alum.wpi.edu/~dkelly/ <http://alum.wpi.edu/%7Edkelly/>
>
>
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