[time-nuts] Practical considerations making a lab standard with an LTE lite

Jim Sanford wb4gcs at wb4gcs.org
Sun Nov 23 15:04:04 EST 2014


I appreciate all the responses to my post earlier today.  Very informative.

First:  DownEast Microwave sells a nice kit for distributing 10 MHz.  
Specs are on their website, but basically, one in, four out -- each 
individually buffered and filtered.

Second:  I will use the 20 MHz from the LTE-Lite to lock a 100Mhz TCXO 
which will be the LO for a high performance 2meter amateur software 
defined radio.  (OpenHPSDR.org for info on the SDR)  I may multiply it 
to help with some of the microwave LOs.  It will also use the 20 Mhz to 
lock a 1GHz TXCO to be multiplied for microwave LOs.

Third:  I will have three of the LTE-Light units.  The first will feed 
some LOs as described above, and the synthesized 10 MHz output will be 
my lab frequency standard.  The lab is in a cinder block room off the 
basement, with 2" of foam insulation under 2 inches of concrete which is 
the floor for a covered porch above.  I'd never thought of it, but the 
"put it on the floor next to a brick wall" idea fits here.  Actually, I 
can put it next to 2 buried brick walls, and will surround it with 
cinder block on the remaining sides.  Can probably cover it with a few 
12x12 paver stones.  NOW, this involves drilling a hole through cinder 
block and drywall between the office/ham shack and the lab.  Would 
rather not, but have to anyway.  I have been "informed" that the fan 
noise from the ham shack gigabit ethernet switch will become politically 
unacceptable in about 72 hours.  (Office/ham shack share a guest 
bedroom.)  I would like to get 1E-10 or 1E-11 accuracy out of this 
setup.  Thanks for this suggestion!

Fourth:  The second unit will be in a building at the base of my antenna 
tower, about 350 feet from the house.  This building is above ground, 
and will be allowed to swing from 45F to 80F over the course of the 
year.  Hence my interest in insulating and heating.  I might consider 
putting something in the ground here, the problem would be access for 
servicing....  I would like to get 1E-10 or 1E-11 accuracy out of this 
unit.  Considered shipping 10 MHz in coax out from the house, would 
rather not, and would like some redundancy, anyway.

Fifth:  I get that the /efc/ vs. /temp/ relationship is very complex and 
accept that trying to characterize it is not worth the effort.  Thanks 
for this bit of information.

Sixth:  My third LTE-Lite will drive a 10MHz reference for a mobile 
("rover") microwave setup, providing the reference for a bunch of GHz 
LOs.  This station will see motion, and temperature variation. Ultra low 
power will not be a concern, so heaters are acceptable. I would be happy 
with 1E-9 accuracy out of this unit.  That translates into 10Hz 
frequency error at 10 GHz.  This kind of frequency accuracy has been 
demonstrated to provide 3+db improvement in the ability to detect weak 
signals -- very significant for microwave weak signal work.

I have pondered all the suggestions about measuring output impedance, 
etc.  For now, I have decided to default to Said's expertise with the 
units and will use one of his suggested circuits as buffers.  Hopefully, 
these will be  on a board inside the HAMMOND box with the LTE-Lite.  
That buffer will drive one of the MMICs to provide additional power to 
drive a filter and then output to the distribution amplifier.  I will 
continue to look for a better idea from one of you smarter than me.

Thanks again for all the insight and ideas.  You guys type and I learn.

wb4gcs at amsat.org

On 11/23/2014 4:46 AM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote:
> I would like to make a unit with multiple 10 MHz 50 Ohm outputs to feed my
> various bits of test equipment.  I am thinking about some practical
> considerations.
> 1) It would be great if there was a circuit published which can give 50 Ohn
> output impedance from a 12-15 power supply,  which
> a) Doesn't load the TCXO
> b) Doesn't degrade the phase noise.
> c) Powered the LTE lite.
> Ideally one for both 10 & 20 MHz crystals.
> Better still if there was a PCB available.
> 2) How should I mount the components?
> My preference would be a metal box with
> * IEC mains socket
> * antenna input socket
> * 9-pin D for reading dats
> * 15  BNC's outputs
> With a power amplifier to provide the output for 15 sockets, some
> ventilation possibly requiring a small amount of forced air cooling would
> be needed. But given the TCXO"s sensitivity to temperature changes, I don't
> know whether it might be preferable to mount the LTE lite in its own box
> without any power supplies in it - perhaps with some thermally insulting
> material around the LTE lite so the crystal doesn't experience any fast
> temperature changes. Then have the power hungry bits completely separately.
> I don't have a particularly big lab, so wherever I mount the LTE lite, the
> temperature is going to change with the air conditioning unit blows hot or
> cold
> There are fairly large temperature changes when I am not using the lab, as
> I don't run the air conditioning unit 24/7.
> I am interested in people's thoughts on the best way to go about this.
> For testing I have a couple of  signal generators that have ovens that are
> powered 24/7. Also I should soon have the SR620.
> Dave.
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