nuckollsr(at)cox.net
Guest
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 Posted: Wed Feb 28, 2007 9:46 am Post subject: Baluns and contactors . . . |
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| Quote: | Hi Bob,
I found your comment about the difference between a coax balun performance
vs. ferrite core balun somewhat contrary to my experience. I am building a
Long EZ and the port rudder has a coax balun (RG58) and the starboard side
has a ferrite balun. The side by side performance (before they were
mounted to the wings) difference between the two antennas is remarkable.
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By what means of measurement? Recall that thousands
of airplanes are flying without benefit of a BALUN
and the owners report "no problems" . . . The article
wasn't intended to persuade anyone to adopt any particular
configuration but was only ONE example of an easy way
to go about it. Figures of merit between configurations
are often so small that they cannot be deduced by operator
observations and yield only to analysis by laboratory
measurement.
| Quote: |
The drawing you have for the balun is not like the balun I built. My
design came from an old navy electronics manual and is significantly
different than what you have shown. In my schematic, the center conductor
between the two elements in the shrink wrap are tied together (actually
never broken), I'll send you a copy of the schematic if I can find it.
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There are a number of ways to make a useful connection
between a feedline and an antenna . . . and a variety
of ways that BALUNS can be fabricated. Each configuration
has characteristics defined by the physics and performance
defined by measurement. But it's unlikely that even side-by-side
comparison by operator observation will produce a clear
"winner". The point of the article was to offer an alternative
to manufactured antennas (whether or not the BALUN is ferrite
or even present) that tend to be pretty expensive.
| Quote: |
Different question. Master Contactor. Is the Cessna Contactor sufficient
for running start power through it ( I don't know how the Cessna is
wired)? Some folks on the web are saying no, that you need something that
will handle 300 amps. I have found some TYCO contactors rated that way -
but they are $90 vs $20 at ACS.
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There are "ratings" and then there are "ratings". Take a
peek at the article on switches at:
http://www.aeroelectric.com/articles/swtchrat.pdf
Relays and contactors are but remotely operated switches.
In addition to make-break contacts, a relay or contactor
has additional considerations concerning its solenoid or
coils.
There have been hundreds of thousands of airplanes
built wherein the 70A "rated" RBMC/White-Rogers/Stancor
contactors have offered satisfactory service life as
a battery master relay even though it's routinely 'overloaded'
during engine cranking. The ability of a device to "carry"
current is several times better than the device's ability
to 'switch' current . . . this is why starter contactors
and battery contactors are built differently. See chapter
in the 'Connection about continuous and intermittent duty
contactors.
Bob . . .
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( IF one aspires to be "world class", )
( what ever you do must be exercised )
( EVERY day . . . )
( R. L. Nuckolls III )
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