[time-nuts] LTE-Lite module

John C. Westmoreland, P.E. john at westmorelandengineering.com
Fri Oct 17 21:37:14 EDT 2014


Said,

What tool(s) did you use to generate that data and output the graph?

Thanks,
John


On Fri, Oct 17, 2014 at 6:10 PM, S. Jackson via time-nuts <
time-nuts at febo.com> wrote:

> Jim,
>
> Here is the resulting 10MHz phase noise plot from the 20MHz TCXO  output:
>
>
> In a message dated 10/17/2014 11:32:49 Pacific Daylight Time,
> SAIDJACK at aol.com writes:
>
>
> Hello Jim,
> let me answer through Time Nuts as this may interest  other parties as
> well.
> Yes, using a fast flip flop to generate 10MHz out  of the 20MHz TCXO 3.0V
> CMOS output from the LTE-Lite module will preserve the  phase noise
> (actually
> improve it by up to 6dB due to the 20log(n/m) noise  improvement) and will
> not add any spurs if you use the clean 3.0V output from  the LTE-Lite
> module
> or an external clean power supply (please note the  LTE-Lite TCXO RF output
> is 3.0V due to the internal 3.3V to 3.0V Low Noise  regulator feeding the
> TCXO and buffer).
> Use fast logic such as 74AC74, 74FCT74, or the  like. We do exactly that on
> our ULN-2550 boards to generate 50MHz and 25MHz  out of the 100MHz, and
> using a fast CMOS divider will result in additive  phase noise that will be
> below the crystal oscillator phase noise  floor.
> That will result in significantly better phase noise  and much lower spurs
> than using the synthesized 10MHz output from the board,  and one 74' chip
> can generate both 10MHz and 5MHz out of the 20MHz LTE-Lite  output. This is
> exactly what we would do here if we needed a clean 10MHz from  the 20MHz
> LTE-Lite board.
> I believe you can order low-noise divide-by-2  blue-top boxes from Wenzel
> already packaged-up and connectorized as  well.
> Hope that helps,
> Said
> Hi Said
> I was one of those looking for 10Mhz but I just thought  again now that it
> might be just as well to divide the standard 20Mhz output by  2 using a FF.
> I think that would preserve all the desirable characteristics of  the 20Mhz
> signal which I understand to just be square wave at CMOS 3.3v  levels
> anyway. Is that correct?
> Thanks
> Jim
>
>
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