[eagle] Re: Preliminary CAN-Do EMI Findings and Suggestions to Mitigate in the 70 cm Receiver

Juan Rivera juan-rivera at sbcglobal.net
Fri Jun 15 07:55:03 PDT 2007


Jim and John,

 

This morning I want to physically move the PCB to the back of the enclosure,
remount the CAN-Do module on the connector plate, and connect them with a
short ribbon cable.  I'll have that done in a few hours and post the results
in my log.

 

Then I'd like to try to filter the switched 13 volts from the module so the
receiver is spur-free and more or less configured the way I think it might
need to go.  Even if the receiver power bypasses the CAN-Do module it looks
like it needs to be able to function with dirty DC power so a simple filter
will probably be necessary in the next revision..

 

Assuming that this removes the spurs from the IF output, that still leaves
us with passband ripple and microphonics to deal with.  I'll remove the
suspect capacitors that John suggests first to see what affect that has on
microphonics.  Then I can make John's suggested modifications to try to
learn more about the ripple.  The problem with these changes is that it will
leave the receiver in a state where running the ATP might not be very
useful.  I think we might want to regroup after I make those changes and see
what makes sense.  We might want to order some film caps to replace the
ceramic chips removed to chase the microphonics and see what John has in
mind for the ripple before running the ATP.  This will push the ATP to the
right by a few weeks but would probably result in more meaningful test
results.  What do you and John think?

 

Juan

 

  _____  

From: Jim Sanford [mailto:wb4gcs at amsat.org] 
Sent: Friday, June 15, 2007 5:21 AM
To: juan-rivera at sbcglobal.net
Cc: eagle at amsat.org; David Smith; Dave Black (Work); Dave Black (Home);
Samsonoff at Mac. Com; Juan.Rivera (Work)
Subject: Re: [eagle] Preliminary CAN-Do EMI Findings and Suggestions to
Mitigate in the 70 cm Receiver

 

Juan:
As usual, good work, and well documented -- thanks!

What is your plan for proceeding to execution of the ATP?

After you've developed a test configuraton and executed/documented the ATP,
I'd like to see a single document, titled "Recommended changes to design,"
which would be the single summary of all you've learned and would recommend
we do different in this design.  As always, I'm open to a better idea.

THanks & 73,
Jim
wb4gcs at amsat.org


Juan Rivera wrote: 

All,

 

I've completed a preliminary evaluation of the CAN-Do RFI problem.  Please
see my log for details by clicking here
<http://www.juanr.com/pages/hobbies/ham_radio/Eagle/CAN-Do_Noise_Troubleshoo
ting.htm> .

 

 

Preliminary Findings...

The spurs seen in the receiver IF enter the receiver in two ways

As radiation from the CAN-Do inductor

Via CAN-Do module switched +14 VDC power on pins 39 and 40

I/O line filtering appears to be unnecessary

The switched power from the CAN-Do module pins 39 and 40 must be filtered

The CAN-Do module will either have to be kept physically separated from any
sensitive components, redesigned, shielded or a combination of the three.

Moving the Can-Do module 2-1/4" forward of its normal location on the
receiver PCB lowers the EMI level below the noise floor.

Suggestions...

Create a full size PCB for the next generation receiver and shift the RF
components to the back of the board (away from the CAN-Do module.)

Add DC input filtering to the receiver

73,

 

Juan

WA6HTP

 





  _____  



 
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