[time-nuts] LTE-Lite module

Jim Sanford wb4gcs at wb4gcs.org
Fri Oct 17 17:06:40 EDT 2014

I look forward to the app note.  Might be the incentive to get me to 
actually USE the Express PCB software I have.....

On 10/17/2014 4:40 PM, S. Jackson via time-nuts wrote:
> Hi there,
> I don't know how much the Wenzel units are, but if someone is not able  to,
> or willing to build one on their own then this could be a  viable
> alternative.
> I will look into writing a short appnote describing how a low-noise
> div-by-2 can be built at home with minimal components using a surface mount '74
> chip and a couple of passives.
> Lastly the 20MHz LTE-Lite boards do generate a 10MHz output of course, and
> if you feed that into a standard counter (5370B, 53132A etc etc) I  think
> the noise floor of the counter would be higher than the  noise floor of the
> synthesized 10MHz output, so you would not see any difference  between using
> the noisier synthesized output and the low-noise 10MHz TCXO  divided output..
> Bye,
> Said
> In a message dated 10/17/2014 13:19:08 Pacific Daylight Time,
> gigneil at gmail.com writes:
> How much would we guess that Wenzel blue-top would run you?
> Relative to the low cost GPSDO,  my understanding is the Wenzel  parts are
> priced appropriately to their quality.
> On Fri, Oct 17, 2014 at 11:32 AM, S. Jackson via  time-nuts
> <_time-nuts at febo.com_ (mailto:time-nuts at febo.com) > wrote:
> 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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