Jim,
I’ll need
the CAN-Do folks to come up with a shielded inductor that will have the same
form, fit, and function.
I know John has
been working on a two-chassis implementation for the receiver to try to get
around the thermal issues that have been raised, but I am personally apprehensive
due to the added complexity of any interconnects that will be required. I
don’t want to beat this milled chassis idea to death but it might be worth
considering from a thermal standpoint. If you had enough thermal mass in
the chassis perhaps it would never have time to reach those extreme low
temperatures during an eclipse, rendering the need for a two-chassis approach
unnecessary. It would eliminate my concern about flexing and with a
milled enclosure you could also move the noisy CAN-Do module into a separate
compartment and filter the power through the common wall.
I’ve been
thinking about DC power distribution in general. Can someone explain the
plan for Eagle to me? In aircraft, at least in the one I am familiar
with, they do not use the chassis as a return. All DC power is treated
the same way as AC power and distributed from a common point as a twisted pair
to minimize common mode noise. Great care is taken to eliminate ground
loops by insuring that the ground returns are back through the twisted pair to
the source and not through a sneak path to the frame.
Juan
From: Jim Sanford [mailto:[email protected]]
Sent: Friday, June 15, 2007 2:16
PM
To:
Cc:
Subject: Re: [eagle] CAN-Do noise
problem is proving to be a difficult one to fix
Juan:
My thoughts:
1. We must stop the radiated noise. Let's try obtaining and placing
a shielded inductor on the CAN-Do! module.
2. I just read a great suggestion from Lou, amplified by a phone call I
just had with Rick, regarding three terminal filter devices. Seems like a
good start.
3. I agree that we need to review the bidding on packaging. That
will probably be the LAST of these issues we take on.
Thanks & 73,
Jim
[email protected]
Juan Rivera wrote:
All,
Please see my write-up here.
The CAN-Do noise is not lending itself to an easy
cure. I think this whole subject of RFI/EMI needs to be looked at
closely. Every payload will be affected by noise on its inputs and can
affect other payloads by creating noise that is propagated back out from within
its module chassis.
With the current scheme, of having a CAN-Do module
located in the same case as the main payload, there are several issues that
need immediate attention:
The CAN-Do module
provides dirty power – both the +13 VDC output and the ground are noisy
The
CAN-Do’s switching power supply inductor, L3, radiates noise that can
affect sensitive circuits several inches away.
Both of these factors are adversely impacting the 70
cm breadboard receiver in the form of 5 kHz spurs on the IF output. As I
mentions earlier, Rather than work to clean up the CAN-Do module immediately,
we should focus on making the receiver function In the presence of this
noise. This approach will result in a more robust design. The
CAN-Do module needs to be cleaned up, but for now it acts as a great real-world
noise generator.
I’m currently out of ideas. I’d like
to hear what you all have to say.
73,
Juan
WA6HTP
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