[time-nuts] LTE-Lite module

SAIDJACK at aol.com SAIDJACK at aol.com
Fri Oct 17 21:11:56 EDT 2014


Some photos of the divider module I built:
 
 
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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