LMS TxLO noise

Andrey Sviyazov andrey.sviyazov at fairwaves.ru
Thu Jul 19 14:29:57 UTC 2012


Sergey.
Is it really so frequently (32k/s updates at 1pps reference)?

Best regards,
Andrey Sviyazov.



2012/7/19 sergey kostanbaev <sergey.kostanbaev at gmail.com>

>
>
> On Thu, Jul 19, 2012 at 6:10 PM, Andrey Sviyazov <
> andrey.sviyazov at fairwaves.ru> wrote:
>
>> Hi all.
>>
>> I've found spurs on the LO noise plot at  ~33kHz and ~66kHz offset when
>> GPS antenna used and position locked.
>> This spurs begin grow up when GPS just near to lock position and after
>> locking spurs stopped to grow as you can see at picture.
>> If thereafter GPS disconnected then noise coming back to normal plot.
>> I think that it is result of 32768Hz clock in the GPS module EB-230, but
>> can't understant how it can impact to 26MHz clock or VCO.
>>
>
> As another idea it can be caused by continues GPS correction lead to DAC
> changes to the VCTXCO.
>
>
>>  Please tell me something who know.
>>
>> Thomas.
>> Was GPS antenna connected when noise measured like on the picture which
>> you sent us (also attached here)?
>> I would to know because of anomal peak near to 30kHz offset too.
>>
>> Best regards,
>> Andrey Sviyazov.
>>
>>
>>
>> 2012/7/19 Andrey Sviyazov <andrey.sviyazov at fairwaves.ru>
>>
>>> Sorry, that was meant to be sent to the mailing list :)
>>>
>>> Best regards,
>>> Andrey Sviyazov.
>>>
>>> ---------- Forwarded message ----------
>>> From: Andrey Sviyazov <andreysviyaz at gmail.com>
>>>  Date: 2012/7/18
>>> Subject: LMS TxLO noise
>>>
>>> Hi Thomas.
>>>
>>> Here forwarded my last e-mail with noise plots when I stopped work
>>> around it at first time, please see below.
>>>
>>> Please try to play around Tx PLL charge pump current (register 0x16) for
>>> better RMS phase stability.
>>> I think we should reach 1 degree or below.
>>>
>>> Alexander gave me the second UmTRX board and after checking and fixing
>>> all known hardware issues<http://code.google.com/p/umtrx/issues/list?can=1&q=&colspec=ID+Type+Status+Priority+Milestone+Owner+Summary+Modified&cells=tiles>I've got roughly the same LO noise plot.
>>> Possible Robin had no time to fixing all of our issues, so check them
>>> all please.
>>> And also check please what type of TCXO installed on your board.
>>>
>>> Best regards,
>>> Andrey Sviyazov.
>>>
>>> ---------- Forwarded message ----------
>>> From: Andrey Sviyazov <andreysviyaz at gmail.com>
>>> Date: 2012/4/13
>>> Subject: Re: LMS TxLO noise
>>>
>>> Hi all.
>>>
>>> There is progress with LMS PLL :)
>>> Pictures are attached here.
>>> t was discovered that 80 kHz spurs come from Ethernet, or rather from
>>> the ET1011.
>>>  I unknowingly put the choke between transistor of 1V regulator and
>>> analog power 1V.
>>> As a result, the regulator has become unstable and oscillated 80 kHz
>>> with amplitude of 200 mV, which climbed into the LMS PLL.
>>> To correct this problem L46 should be replaced by jumper on all alfa
>>> version PCB's.
>>>
>>> Also I just played with current in the PLL loop, shown on the picture
>>> for clarity.
>>> Proved to be the optimal current 1,9 mA (you should write 0x93 in the
>>> register of 0x16).
>>> But, I think, for the RxPLL will be better use of the current 2.4 mA,
>>> because the nearest noises more important for Rx (you should write 0x98 in
>>> the register 0x26).
>>>
>>> Best regards,
>>> Andrey Sviyazov.
>>>
>>>
>>>
>>
>
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