I look forward to the app note. Might be the incentive to get me to
actually USE the Express PCB software I have.....
Jim
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,
gign...@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@febo.com_ (mailto:time-nuts@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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