[USRP-users] Master Clock Supression

Michael West michael.west at ettus.com
Tue Jul 21 21:02:15 EDT 2015


Hi Devin,

Since you don't see the harmonics when connected to a spectrum analyzer, I
don't think there is any leakage happening with the ADC (or anything on the
TX side).  If possible, I suggest hooking up a signal generator to the RX
side to see if you can see the harmonics.  If you do see them, please
provide more detail about the levels of the tones and your settings (freq,
gain, siggen freq, siggen level, etc...).

I have also been assuming you are using the latest version of UHD (3.8.4).
If not, please be sure you are.

Regards,
Michael

On Tue, Jul 21, 2015 at 3:19 PM, devin kelly via USRP-users <
usrp-users at lists.ettus.com> wrote:

> So the master clock could be leaking on the X310 mainboard into the ADC.
> Would that mean that you can get the clock to leak over to the ADC
> regardless of the daughtercard being used?  Does anyone else see these
> tones every 200 MHz or is it just me?
>
> Devin
>
> On Mon, Jul 20, 2015 at 5:36 PM, Michael West via USRP-users <
> usrp-users at lists.ettus.com> wrote:
>
>> A further point of clarity.  The clock being fed to the UBX boards on
>> X310 is 50 MHz (1/4 the master clock rate).  The full 200 MHz master clock
>> is being fed to the FPGA, DACs, and ADCs.  On the X310, the DACs  and ADCs
>> are under the daughter boards and the clocking circuitry is between them.
>>
>> Regards,
>> Michael
>>
>> On Fri, Jul 17, 2015 at 2:16 PM, Marcus D. Leech via USRP-users <
>> usrp-users at lists.ettus.com> wrote:
>>
>>>  On 07/17/2015 03:49 PM, devin kelly via USRP-users wrote:
>>>
>>> Also, I haven't calibrated either unit.  Could that be a factor in
>>> this?  While I'm bringing this up, if I do calibrate these, or any other
>>> USRPs I have with daughtercards, I run the calibration with all the SMA
>>> ports open, right?  No cables, terminators, etc.
>>>
>>>  Devin
>>>
>>> Yeah, just open should work OK.
>>>
>>>
>>>
>>> On Fri, Jul 17, 2015 at 3:45 PM, devin kelly <dwwkelly at gmail.com> 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
>>>>
>>>> On Fri, Jul 17, 2015 at 3:15 PM, <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> 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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>>>>>>
>>>>>>
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>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> http://alum.wpi.edu/~dkelly/
>>>>>
>>>>> _______________________________________________
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>>>>>
>>>>>
>>>>
>>>>
>>>>  --
>>>> http://alum.wpi.edu/~dkelly/
>>>>
>>>
>>>
>>>
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>
>
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