[time-nuts] FE-5680A Results so far

Peter Bell bell.peter at gmail.com
Fri Dec 30 00:12:54 EST 2011


Just FYI, this current batch of FE-5680As has a different RF
architecture than the old ones - one of the most notable changes is
that although they still have a DDS in them it's not in the output
path anymore - the VCXO now runs at 60MHz, and this is divided down
(in a CPLD) to produce the 10MHz output - so it's likely that your
output measurements are not really applicable to these units.

On Fri, Dec 30, 2011 at 2:37 AM, Said Jackson <saidjack at aol.com> wrote:
> Hello Mike,
>
> We measured a couple of these 5680As on a tsc5125a analyzer. With different quality supplies.
>
> Very noisy buggers, huge number of spurs and very high noise floor -130dBc or so if I recall correctly. Thats probably the jitter you are seeing. Probably due to the dds generating the output not a crystal.
>
> ADEV was parts in E-011 while good, not very good.
>
> Frequency accuracy was +5E-010 then tap the box hard and it goes to -1ppb.
>
> Good enough as a portable frequency counter reference, as the offset can be compensated, and the output is fairly stable...
>
> These units could really use gps disciplining and a crystal post filter.
>
> Great stuff for $40, new they must have been over $1000.
>
> Bye,
> Said
>
>
>
>
>
>
>
>
>
> On Dec 29, 2011, at 1:14, mike cook <michael.cook at sfr.fr> wrote:
>
>> Hi,
>> Just got my cheapo 5680A.  It was accompanied by a little teddy bear clutching a L7805CV !
>>
>> Got a couple of questions.
>>
>> 1) What is the expected 10MHz peak to peak voltage.  FEI doc seems to indicate 0,5V but I am getting only 200mv.
>> 2) What is the sensitivity to 15V input level. I am only measuring 14,722 (stable) on Pin1.
>> 3) Could this low input voltage affect output voltage?
>>
>> The box locks after a couple of minutes but my TDS 210 is showing a very jittery  ( 9,98-10,02 MHz ) but well formed sine wave for 8 hours of being powered on.  Could this also be an artefact of low main power?
>>
>> rega
>> Mike
>>
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