LMS TxLO noise

Andrey Sviyazov andrey.sviyazov at fairwaves.ru
Thu Jul 19 14:10:56 UTC 2012


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.
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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