nuckolls.bob(at)aeroelect
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 Posted: Sat Jul 06, 2019 4:47 pm Post subject: Balun article |
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At 10:26 AM 7/6/2019, you wrote:
Now that's a mystery . . .
One would think that RAMMI knows what they're
doing.
20" elements do not conform to legacy
antenna design rules . . . but we don't
know what matching components might
be included inside their mounting base.
It would be cool to put an antenna
analyzer on the antenna and see what
it looks like.
The pictures I can see of the RAMMI coax
cable with integral balun suggests
that they've fabricated a design like
this on the end.
I've seen this design in documentation for
aviation radios . . . in fact, we find it
in AC43-13 dated 2008 and . . .
[img]cid:.0[/img]
in this illustration taken from the installation
manual circa 1949 for a Lear LTRA6 transceiver
[img]cid:.1[/img]
Where Item 7 is called out as a 63184-02
Transmission Line Assembly but without
further details as to how it's constructed.
The design is echoed on numerous websites
as an 'aviation antenna balun'.
Two flies in the ointment: First the callout
for "1/4 wave" is not defined. Free air or
in coax. Second, the balun is noted in an
article by a competent observer of things
electronic where he states, "Lab tests
do not confirm that this balun works."
[img]cid:.2[/img]
Okay then . . . when I'm ready to put the
signal generator on Jim Weir's dual band
ELT antenna to investigate common mode chokes,
I'll be able (1)to confirm/deny the functionality
of this design (2) reconfirm functionality
of the Pawsey Stub balun described in many
articles and echoed on my website and (3)
see if a ferrite core common mode choke would
be a less fussy way to mate coax to the cat-whisker
vor antenna.
In the mean time, know that back in the dark
ages, Cessna Pawnee plant fiddled with various
baluns for the whiskers . . . they even might
have tried the design above. I do know that a
whole lot of airplanes were built with coax attached
directly to the antenna with NO balun . . .
VOR signals are strong, distance from aircraft
to vor stations at the changeover point along
published airways is never so far that a really
lousy antenna wouldn't work. I think Cessna
had more trouble with process and manufactured
fragility than with radio performance . . . they
quit using them entirely for a time.
That still leaves the question about your RAMMI
antenna with 20" whiskers. If you just hooked
your feedline directly to the RAMMI antenna,
chances are you'll never know the difference.
Bob . . .
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