Sender: <marvkaye@lancaironline.net> (Marvin Kaye)
To: lml
Date: Wed, 17 Apr 2002 01:05:00 -0400
Message-ID: <redirect-1166882@logan.com>
From: Adam Molny <amolny@optonline.net>
Subject: More on Ritchie Electronic Compass
MIME-version: 1.0
Content-type: text/plain; charset=us-ascii
Content-transfer-encoding: 7BIT
References: <20020415040416.AAA1850@pop3.olsusa.com>

> If, by "self-appointed authority,
> you mean the certifying entities within the FAA, then their standards
> for avionics performance have racked up a pretty impressive record for
> safe operation.

I've flown behind certified avionics truly awful, with Cessna autopilots
as a prime example. Also, the LED displays on our Bendix King Silver
Crown radios failed regularly. FAA certification does not neccesarily
guarantee quality or reliability.

> <<<...The wiring problem may be as simple as adding RF chokes
> (little iron donuts) to the device's power lines...>>>
> 
> I guess the PhD's who developed SFS
>  are really lamenting the fact that they didn't have your BSEE available to
> them. I'll bet choke cores are much cheaper than the ASIC's, shielding, and
> other technology they used to refine the RF immunity embodied therein.

You shouldn't be intimidated by the challenge of adding noise
suppression to a circuit board, it's really quite simple. Decoupling
capacitors throughout the board connect the power and ground planes, a
passive filter cleans up the incoming power, and shielding is nothing
more than strategically placed sheet metal which is bonded to analog
gound. Custom ASICs are unrelated to the noise issue.

> 
>  >There are simple, well-known measures which can be taken
>  >to alleviate the problem....
>
> The methods you have described are the correct approach to take to fix 
> an inadequately designed product. 
> There are just as well known and significantly more effective measures
> to deal with the RF problems during the design phase...

We are really talking about internal versus external noise suppression.
If I buy a $30,000 EFIS, I certainly expect it to hook directly to the
avionics power bus and have it work under all conditions.  If my $60
electronic compass requires external filtering to tolerate spikes and
dips in voltage, I am willing to spend a few dollars on external
components, and devote some time to get it working.

It all boils down to time versus money. You can spend lots of money and
save hundreds of build hours (Lancair has really spoiled us in this
area), or you build on a budget, and do more work yourself. Every
builder strikes his own balance, and no one answer is right for
everybody. 

-Adam Molny
Legacy #151