Alexandre Guimaraes wrote:

>  Has anyone tried to connect something like a J-pole antenna to one of
> these modules??  How could I do the coupling of such an antenna?  The
> 2.15 Db gain would be really nice for reception and the antenna could
> be made with very simple 300 ohms parallel antena wire.

  The so-called "J-pole" and its popularity, or rather the enthusiasm it
engenders, really gets under my skin!

  A "J-pole" is in fact a half-wave dipole, nothing more, nothing less,
end-fed by a non-radiating stub.  Its gain probably is 2.15DbI, the "I"
standing for "isotropic" whcih is the radiation pattern of some
theoretical antenna radiating equally in all directions, something that
is in practice *very* difficult to do.  Naturally, *any* antenna that
radiates more energy in some directions and less in others will have
"gain" over isotropic, unless it is resistive (converts power to heat).

  When a quarter-wave sits on a ground plane, the element is supposed
to be "reflected" in the ground plane; that is, it behaves as if the
other half of a half-wave dipole is present; it effectively *is* a
dipole.  The only differences between this and a half-wave dipole are a
slight distortion of pattern by the ground plane (and this depends on
the slant {conical} of the ground plane), and the feed impedance which
depends on a lot of things.

  Conclusion:  Half-wave dipole or J-pole has no gain compared to
quarter-wave ground-plane.  Its advantages are that it is more compact
(no ground plane) and that the active element is held a quarter-wave
distant from the mounting point (good for cars!).  Tuning consists of
adjusting the length of the active element *or* the stub and the tapping
point of the feed up the stub (or use a loop or "gamma" match with a
trimmer).  But at these frequencies, end-feeding a half-wave with a
simple wire-loop inductor and trimmer cap may be just as easy.

  Tune-up is probably best done using a signal strength meter at these
frequencies.

  Cheers,
        Paul B.