[time-nuts] Frequency counter recommendation

Dave M dgminala at mediacombb.net
Tue Dec 21 17:53:46 UTC 2010


I'd like to input a few suggestions regarding layout and construction, 
namely, the PCB material and the form factor.

I suggest that any circuitry processing signals over about 2-3 GHz be 
constructed on a PTFE or PTFE/ceramic PCB material, such as Rogers RT/Duroid 
(www.rogerscorp.com/). Arlon (arlon-med.com) also markets similar PCB 
material.  The lower frequency circuitry can be made on FR4 or equivalent.

As to the modularity, I suggest that modules be made so that they are 
stackable, but not attached to each other directly, but through a 24, 30 or 
40-pin (or whatever width is necessary) ribbon cable on the rear.  The cable 
would have IDC card-edge connectors spaced so that they could attach to all 
modules. Similar to the arrangement that older PCs had to interconnect 
floppy and hard disk drives.   The modules would be stacked on top of each 
other, using aluminum or steel threaded spacers.  That way, no card cage, 
intermodule interface system or back plane would be needed.  Physical size 
could be determined at PCB layout time.  Build all modules to be stacked, 
using the smallest size that would accommodate all modules.  Any RF In/out 
connectors or displays could be brought out on the front edge of the 
modules, and extended to the front of whatever chassis the user chooses by 
short extension wires/cables.

As to the production issue, if these boards are envisioned to be distributed 
in kit form, I suggest that consideration be given to the possibility of 
having a fab house fix the small, high pin count parts to the PCB and leave 
the larger, easier to solder parts for the kit builder to assemble.  On the 
other hand, it is probably just as cheap to have the whole board stuffed and 
soldered than only a few ICs.  That's a decision to be made by the PCB 
manager.

I agree with the power supply approach that all supplies would be user 
supplied, with a STRONG recommendation that all supplies be linear.  SMPS 
supplies could be used at the users' risk.

Thanks for listening,
David
dgminala at mediacombb dot net




More information about the Time-nuts_lists.febo.com mailing list