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RE: [Discuss-gnuradio] GPS for USRP ideas

From: Krzysztof Kamieniecki
Subject: RE: [Discuss-gnuradio] GPS for USRP ideas
Date: Thu, 25 May 2006 22:22:38 -0000
User-agent: Internet Messaging Program (IMP) 3.2.2

Quoting "Whitaker, Brian" <address@hidden>:
> Humph... 
> I think maybe the answer to this is that 100kHz is outside of the loop BW of
> both of these applications; this means the the phase noise is really just a
> function of the VCO itself. I would have expected that the inherent phase
> noise of the 2118's VCO would have been worse than the 2740 (for the Kvco
> alone)... so I'm guessing that the 2740's VCO just plain stinks. In Maxim's
> defense, it's a really old part (pre SiGe, even!)
> So remember that the close-in phase noise is mostly dependent on the
> reference and the noise generated from the PLL itself (FM modulates VCO,
> lots of noise + high tuning gain Kvco => higher noise in PLL BW). It's
> pretty tough to compare phase noise unless you know about the references
> used and the loop BW and such.

I'll try to trackdown information about the respective PLLs.

> I had always thought that a USRP board from one of these sat tuners would be
> a good general-purpose receiver... but Krys has the Microtune TV tuner
> boards done already -- I'd suggest working with those and just see what
> issues people run into in trying to use this for GPS. 

I had nothing to do with the Microtune tuner boards, but I'll take the credit

> Also -- I'd suggest not designing a USRP board around the 2740. There are
> better front-ends out there.
> One last thing -- Krys, you said something about the 2116/8's not needing an
> external reference?  Pins 21/22 are for the XTAL -- the part has an internal
> reference oscillator, but that just means that we provide the positive-fb
> amplifier that rings against the (passive) crystal. Tuners that don't have
> this require a 'reference oscillator' (often 'TCXO') module that includes
> the passive resonator along with the active oscillator circuit.  IC mfg's
> are busy trying to design out everyone in the app ckt they can, but no one
> has built an on-chip crystal reference :)

I meant that the 2116/2118 Evaluation Board does not need an external reference,
while the 2740 Evaluation Board does.

What is the price of the 2116/8 Evaluation Board?

> Brian.

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