Paul McAllister wrote:
> My understanding is that the balun is needed to match impedances to prevent
> reflected energy passing up the coaxial braid. If the antenna is for
> receiving only is a balun even required ?
Yes it is. If it is unbalanced, only a fraction
of the signal makes it way to the RF input (law of
reciprocity, they call it).
> Are ferrite beads on the outside of the coaxial cable effective in doing
> this ? In the Europa manual they show a simple dipole constructed like this.
Jim Weir of RST Engineering is a proponent of the
beads and says yes. Bob Archer makes an
alternative style of balun, and he says beads do
little but trap RF energy. Of course, they're
competitors. But Weir says also that a coaxial
balun works well too, but is more "peaky". If you
buy the foil tape antenna kit from Weir
(www.rst-engr.com), he tells you how, in an
excellent booklet that accompanies the kit.
> Since the 3 frequencies are almost multiples of each other, can I construct
> or purchase a splitter that will allow me to connect all 3 to the one
> antenna ?
The same Jim Weir booklet describes a splitter
that works well, and cost little. But for NAV and
GS only. The marker frequency isn't really a
sub-harmonic (75 mHz); the antenna must be
oriented longitudinally; and the sensitivity of MB
receivers (and station xmit power) is such that
they need a proper antenna. That's in order to
clearly and briefly identify station passage.
---From experience, I've seen where if you adjust up
the receiver's sensitivity to match a bad antenna,
you hear the LOM's boop-boop for miles along the
LOC's path, but never see the stinkin' blue
light. Very bad, while shooting an ILS in the
soup.
Hope this helps!
Regards,
Fred Fillinger, A063
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