[time-nuts] Rooftop antenna and splitter

[Achim Gratz]

Denny Page via time-nuts writes:
> No, no ground plane. Don’t really have a lot of room for that in the
> window. Out of curiosity, how large of an impact have you found with a
> ground plane?

As long as we're talking ceramic patch (puck) antennas, I've seen around
15dB improvement repeatedly (as reported by the receiver statistics)
with otherwise non-optimal placement of the antenna (indoors, viewing
the sky through a wooden roof covered with rolled roofing).  

As mentioned elsewhere in the thread, the better antennas come with
their own (optimized) ground plane if they need one.  Good luck finding
data sheets for the puck antennas, but if you do get hold of one,
sometimes they do show how the directivity changes with different sized
ground planes.  If you have a magnetic puck you best use a magnetic
steel surface, the cap of a large diameter can works quite well also.
Otherwise aluminum foil is just as effective and easily cut or folded
away if you want to try to exclude reflections.

With multiple active patch antennas going to different receivers, I've
found that at least the antennas I have do not like to be placed very
close to each other.  Spacing them at least half a wavelength from each
other seems to take care of that.  If the backside shield of the active
patch antenna is connected to ground, then the ground plane must be
isolated from all (but possibly one) antenna; otherwise the resulting
ground loop will degrade reception.


Regards,
Achim.
-- 
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