nuckollsr(at)cox.net
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 Posted: Mon Mar 12, 2007 5:53 am Post subject: Putting things into perspective |
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Re: locations of electrowhizzies in the airplane . . .
Let's consider some tidbits from recent comments about
location.
>All this talk about transponder "Antenna" locations
>has me thinking about the location of the transponder
>itself. Will my Becker 2 1/4" transponder (250watt)
>be "polite" to the Trutrak autopilot sitting next to
>it within 1/4"? Or should I locate a less critical
>device in the hole right next to the transponder?
>If so which device would likely get along in close
>proximity with the transponder?
>Voltmeter, electronic fuel gauge, electronic tach, electronic clock?
. . . and
>The Comant antenna folks in their installation instructions
>specify a minimum of 36 inches IF possible. Further apart
>IS better. But, closer will USUALLY work!
In virtually every manufacturer's installation
manuals, we find various and sundry recommendations
to be considered if the owner wants optimum
performance from the product. Batteries are
accompanied with suggested maximum recharge
currents, temperature compensated charging
and float voltages, etc. Antennas, it's suggested,
should be located no closer than n-inches to
another antenna or conductive materials. Radio
installations should be cooled and/or isolated
from heat sources. Tires should be checked for
inflation and held at such-and-such pressures,
etc.
What's never included in these instructions are
quantified or qualified consequences for failure
to observe these admonitions to the letter. There
are a variety of possibilities. First, suppose a
manufacturer spells out a lot of detailed instructions
for optimum performance and for some reason, the
customer comes back with a complaint. It's an
easy CYA action to ask, "Well, did you follow all
the recommendations?" Another possibility is that
while the recommendations are based on laboratory
conditions deduced during product development, there
were no quantified studies that detail the consequences
for letting the recharge voltage stray from optimum
by n-volts, or allowing some piece of a transceiver
to exceed optimum by n-degrees of temperature. It's
left up to installer and operator to discover these
things for themselves. Degrees of concern range from
a notion that practical deviations from optimum
are known to have little significance . . . others
worry to the point of obsession with concerns that
departures from optimum pose a threat of unsatisfactory
performance if not catastrophic hazard to the device.
These are the things that system integrators learn
while the manufacturers are relatively content to
coast along offering best-of-all-worlds conditions
for optimum performance of their product. In real life,
many products live and work in less than "ideal"
situations yet they perform in a manner that the
user perceives as satisfactory. In the vast majority
of cases, we'll never know how the vhf comm and
transponder systems affect each other if the
antennas are only 23 inches apart or how many more
flights we might get from a battery that is charged
at 14.6 versus 14.4 volts.
The point of all this is an attempt to assuage
unnecessary concerns for slicing and dicing
installation and operational considerations with
some notion that we'll perceive a real return on
investment for the effort. Virtually every time
someone pops up on the list with a real performance
problem, root cause for their perceptions turns out
to be rather gross errors of installation. Wires
crossed, ground loops, coax connector loose,
perhaps the piece of equipment was never intended
to be used that way . . . or maybe something is
just broke or worn out.
The golden rule of thumb is do as much as is
practical to comply with the manufacturer's
best wishes. Get on a community List like this
and see what insight the experience base of the system
integrators has to offer. Keep the knowledge of
compromises you made in your hip pocket to
examine as possible causes for problems that
probably wont but may manifest later. By so
doing, you gain knowledge that adds to your
own skills as a system integrator that can
be shared with others at some time in the
future.
Bob . . .
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