[time-nuts] LTE-Lite module
SAIDJACK at aol.com
SAIDJACK at aol.com
Sat Oct 18 14:19:24 EDT 2014
lots of questions, let me try to answer some of these. Bob, David, et. al,
thanks for answering some of these already!
Dave, as Bob said "it depends on your application" -- and your time frame.
Also, please check the FAQ for an answer on the external TCXO requirement,
specifically item 35. in the FAQ on the Ebay website for the product.
Jim, I ended up doing the "appnote" in email format, and sending out a
description, schematics, PN plot, and photos yesterday, please check your
emails. I won't do a formal appnote, sorry no time.. I hope the description of
what I wired-up yesterday is good enough for folks to try the same.
Ernie, as mentioned here the price is $185 plus shipping on Ebay for the
entire kit. Shipping is calculated by Ebay, and should be a flat-rate of $10
in the continental US
Hal, MY BAD!! I should have known better and super-imposed both the
original 20MHz and 10MHz plots on the same plot. I will do so shortly. On the
table in the plot: the TimePod tries to determine spurs, and display them on
the upper right hand of the plot in a table, and with the phase noise being
as clean as it is I guess the TimePod software could only find two spurs,
one at 0.8 and one at 0.9Hz offset from carrier, which was not even shown in
that plot since it starts at 1Hz.
Thanks so much for your feedback, lively discussion, and good questions
I hope that answers all questions,
In a message dated 10/18/2014 10:43:40 Pacific Daylight Time, kb8tq at n1k.org
For a lab reference, “clean” is a relative term. Most (as in every one I’
ve ever seen) instruments expect a dirty signal on the reference input.
They phase lock an internal oscillator to clean it up. Past some
(unfortunately variable) offset, the reference signal has no impact on the instrument at
all. In most cases, that offset is below 50 Hz in order to reject power
line induced spurs on the reference signal. Yes, phase noise inside 10 or 20
Hz may matter. ADEV at 1 sec and longer is probably a better thing to look
How good does it need to be? Most counters are quite happy with an ADEV at
the 1x10^-11 level at 1 second. VNA’s and spectrum analyzers will be happy
with something even less stable. Synthesizers will (ultimately) pass along
what ever is on the reference to the output. Your specific test
application will dictate if a 1x10^-12 wander at 100,000 seconds on your synthesizer
is important or not.
> On Oct 18, 2014, at 9:34 AM, Dr. David Kirkby (Kirkby Microwave Ltd)
<drkirkby at kirkbymicrowave.co.uk> wrote:
> On 17 Oct 2014 19:33, "S. Jackson via time-nuts" <time-nuts at febo.com>
>> 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
>> 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)
> Hi Said,
> I am only looking for a good clean 10 MHz reference for my lab to feed
> 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
> 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
> than the inbuilt TCXO. Without knowing what your board expects to see, it
> is impossible to know what to type to add.
> and will
>> 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
>> than using the synthesized 10MHz output from the board, and one 74'
>> 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
>> 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
>> 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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