LMS TxLO noise

sergey kostanbaev sergey.kostanbaev at gmail.com
Thu Jul 19 14:23:48 UTC 2012


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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