[eagle] Receiver Spec vs. ATP, a few Suggestions and a Question or Two

Juan Rivera juan-rivera at sbcglobal.net
Fri Jul 27 21:23:00 PDT 2007


John,

 

I took a few minutes to look over your new specs and compare them against
the Acceptance Test Procedure.  I've got a number of tests in the ATP for
which there are no specs:

 

*         Image rejection

*         Internally generated spurs

*         Local oscillator leakage

*         Input and Output VSWR

 

Items that need to be addressed that aren't in either document:

 

*         EMI conducted susceptibility

*         EMI radiated susceptibility

*         Short and long-term frequency stability

 

I also take issue with the -60C minimum power-down temperature.  I think
this is unrealistic just from a CTE mismatch perspective.  The reliability
of anything subjected to that wide a temperature spread is going to suffer.
A way must be found to raise that temperature.

 

I have a few thoughts...  The CAN-Do switching step-down converter is only
supplying 11 milliamps.  If we take a slight efficiency hit we could just go
to a simple linear regulator and completely eliminate the radiated and
conducted EMI emission problem from CAN-do.  That eases the EMI filtering
and shielding requirements for every single payload.  That seems like a good
trade-off to me.

 

Rather than worry about trying to conduct heat through a PCB why not just go
to externally mounted regulators for the CAN-Do and the Receiver right on
the case itself.  We're not that pressed for space.  That eases the heat
sink and the associated thermal gap filler issues.  EMI will still be an
issue, but only for external sources instead of one that is inside the
enclosure itself.  That strikes me as a huge bonus.  Why not design a
single-sided PCB with the regulators hanging over the edge and the whole
assembly, PCB and regulators, mounted directly to the enclosure.  Stick it
in with the CAN-Do module in a separate cell.  Filter all the signal and
power through the common bulkhead.

 

I'm also curious as to why you are specifying two different types of SMA
connectors.

 

73,

 

Juan - WA6HTP

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