[time-nuts] Efratom 10Mhz frequency standard from Fluke.l

[EB4APL]

David,

I I told yesterday it was too late for writing an explanation.  Here it is.

I bought one of these units around last June, my intended use was to 
distribute the 10 MHz from my Rb oscillator to be used as the reference 
for various synthesizers and counters in my home lab.  I didn't put it 
to use yet, but I made some test with the gadget and this is what I found:

- The power supply should be some 15V, not 12 as announced.  There is a 
3 pin 12 volt linear regulator7812CT which needs some overhead to work, 
and a DC-DC converter to generate +5V which is specified at 15V input 
and in fact it doesn't work well below it.

- The 10 MHz oscillator is a EFRATOM 105243-003 and there is a jumper 
for selecting this oscillator or an external 10 MHz input.  The circuit 
has a 8.7 V regulator built with a 431 programmable zener with an opamp 
and a multiturn pot which is accessible from outside for adjusting the 
oscillator frequency.  There is also a hole in the oscillator for 
adjusting the frequency.

- The oscillator output is squared with an unknown comparator and fed to 
the inputs of what seems to be a 74ACT244DW which 8 outputs drive the 
output connectors through coupling networks.  The PCB has provisions for 
8 SMA output connectors, with only 4 populated.  I bought a bunch of 
identical connectors from other supplier and I'll install them when I'll 
put the unit into operation, I'll only have to drill 4 holes for them in 
the case and solder the output networks, nothing critical.

- Currently the unit has 2 output networks configured for square wave 
output (just a 50 ohm resistor in series) and the 2 remaining for sine 
wave output.  In this case the network consist on a 50 Ohm series 
resistor, a pi LC filter a and a series capacitor. According to the 
silkscreen labels it was the manufacturer intended configuration.  It is 
easy to transform any output for square or sine because the parts are 
smd but of reasonable size.

- I don't have the means to measure the jitter or phase noise introduced 
by this schema, but any expert here could give his opinion about it.  
The ovenized oscillator on my unit doesn't perform very well in terms of 
aging or time to stabilize, it is worse that my other oscillators ( ) 
from the same source, I compared them with my Rb and maybe I didn't 
waited enough days, but anyway the others 2 were very stable after 1 
week and this one not.

-. I don't know the exact parts used for the comparator and the buffer 
because the tops have been filed.  When I reverse engineered the 
schematic I offered it to fluke.l, in the believe that it could be 
useful for his customers but his answer suggested that he had filed the 
IDs in the fear of other Chinese competition could copy his 
modifications and refused to give me the parts numbers.

If you want more info don't hesitate to ask for it.

Regards,
Ignacio, EB4APL



El 12/02/2011 22:03, Dave M wrote:
> Does anyone have any experience or knowledge of the "Efratom Multiplexed
> output 10Mhz frequency standard" from Fluke.l on EBay (item 290329156915)?
> I wonder if it could be used as a distribution amp, but no details about
> output impedance, output current capability, etc.  He indicates that the
> output voltage is 1.8 - 2.3 volts (doesn't say if it's open circuit or
> terminated).  From the images on the listing, looks like he didn't terminate
> any of the lines to the counters or scopes.
>
> Thanks
> David
> dgminala at mediacombb dot net
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