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@amsat.org]
Sent: Friday, June 15, 2007 5:21
AM
To:
Cc:
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@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.
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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