[time-nuts] LTE-Lite module
Dr. David Kirkby (Kirkby Microwave Ltd)
drkirkby at kirkbymicrowave.co.uk
Sat Oct 18 09:34:48 EDT 2014
On 17 Oct 2014 19:33, "S. Jackson via time-nuts" <time-nuts at febo.com> wrote:
> Hello Jim,
> let me answer through Time Nuts as this may interest other parties as
> 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
> improve it by up to 6dB due to the 20log(n/m) noise improvement)
I am only looking for a good clean 10 MHz reference for my lab to feed into
instruments like my SA, VNA, signal generator etc. Would I be right in
concluding the best way to achieve this is to use the 20 MHz version and
the simple divide by 2 that you showed?
I was going to place an order for the 10 MHz version, despite the long lead
time, but if I understand you correctly I would get better performance in
less time by going for the 20 MHz version and a ÷2.
The other thing I am not so sure about is what the specification of the
external TCXO/OCXO needs to be. I gather it is 3.3 V, but does it need to
generate a sine or square wave? What amolitude? I was wondering if there
would be some advantage in using a 10 MHz OCXO, such as an HP 10811A rather
than the inbuilt TCXO. Without knowing what your board expects to see, it
is impossible to know what to type to add.
> not add any spurs if you use the clean 3.0V output from the LTE-Lite
> or an external clean power supply (please note the LTE-Lite TCXO RF
> 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
> 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
> 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,
> 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
> I think that would preserve all the desirable characteristics of the
> signal which I understand to just be square wave at CMOS 3.3v levels
> anyway. Is that correct?
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