[time-nuts] LTE-Lite module

SAIDJACK at aol.com SAIDJACK at aol.com
Fri Oct 17 21:54:37 EDT 2014


John,
 
I used John Miles Timepod and associated application software, now  
available from Microsemi, and highly recommended. I fed the output of the DFF  
directly into the timepod (via a DC-block and 33 Ohms series resistor).
 
The reference was an HP 58503A GPSDO which limits the noise floor of the  
measurement a bit.
 
bye,
Said
 
 
In a message dated 10/17/2014 18:45:11 Pacific Daylight Time,  
john at westmorelandengineering.com writes:

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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