[time-nuts] Changing FE-5650A frequency?

Alexander Wright alecjw at gmail.com
Sun Apr 7 13:26:37 EDT 2013


On 07/04/13 17:56, Robert Atkinson wrote:
> Hi Alex,
> These units were used as timing references for secure communication systems (Havequick). see ebay item 130832014630. Unfortunatly they are an older design with a two chip DDS. The other problem is that the "M" designation is for military and means they have been partially encapsulated with polyurethene foam. You can cut it away but it is very easy to damage the PCB. Frequency setting is by DIP switches (under the foam) allowing full range of frequency selection. However the output filter is narrow so you can't go far from 800kHz.
> Did you buy all seven?
>
> Robert G8RPI.
>
>
Robert,
Thanks for the info! I bought one of these wondering what they were, 
took it apart and found the rubidium clock and figured it must be worth 
something (more than the 15 quid he was asking) so I bought the remaining 6!

I've taken the foam off the top PCB and i've found that there's a 
12.8MHz signal being produced which is then being divided down with an 
800kHz logic chip. I should imagine the filter must be on the circuit 
board below? I might try changing the frequency
of the DDS chip, removing the frequency divider and tinkering with the 
output filter. Do you have any info on what sort of filter I should 
expect to find?

Thanks,
Alec M0TEI


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