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Re: Re: S-Band Antenna Comparisons, etc.



OK, Bob,  I missed the part about the quote from Kraus.  I stand corrected.  Your point makes sense.

73,

Jon
NA9D

Bob Snyder <kd1vv@mediaone.net> wrote:
> Not to belabor the point, but the reflector absolutely DOES influence
the polarization of the signal received (or transmitted) by the feed, if
it's not solid or fine mesh.  Reflectors reflect by having currents
induced on them.  That's why their surfaces must be conductive. 
Circular polarization induces circular currents, which can't flow on a
reflector with just parallel wires.  Think of the bar-b-que reflector as
a polarization filter.  Try to illuminate it with a circularly polarized
feed, and out comes linear polarized signals. Only the vertical (i.e.
parallel to the reflector wires) polarization component is reflected;
the horizontal component goes right through.

Re-read Joe's (K0VTY) post earlier this morning.  He cites Kraus to
verify this point.  It's also mentioned in Johnson's "Antenna
Engineering Handbook" (3rd ed. pg.30-19).

Bob


Jon Ogden wrote:
> 
> on 1/7/01 4:08 PM, NS1Z at ns1z@arrl.net wrote:
> 
> > Hmmmm?? Is the spacing of the framework that bad? Usually the design is such
> > that it approximates a full metal back but is ribbed to lighten it and
> > reduce (!) wind resistance.... Something about waveguide beyond cutoff?????
> 
> The reflector is just that -> it reflects RF power to the feed.  So it
> matters not which way the reflector grill runs.  As Dave Tipton pointed out,
> what matters is the feed.
> 
> Your comment about reducing wind resistance or wind loading is interesting.
> This is the conventional wisdom behind these.  However, I've talked to at
> least one cellular/PCS operator up in my area about these.  He hates them
> and uses solid dishes.  He said solid dishes have LESS windloading in
> conditions of heavy ice and snow.  He said ice build up on the BBQ antennas
> creates a tremendous load on it.  So he didn't use them.  Good point.  I
> suppose that those of you down south who don't have regular ice or snow
> build up wouldn't find that a problem.  But to anyone who has a regular
> winter like we are having in Chicago, think twice about getting a BBQ dish.
> In fact, its even worse for folks in say, St. Louis where you get more ice
> storms than we do.  You get ice built up on that sucker and it will get
> HEAVY and you gain in windloading surface area as well.
> 
> 73,
> 
> Jon
> NA9D
> 
> -------------------------------------
> Jon Ogden
> NA9D (ex: KE9NA)
> 
> Member:  ARRL, AMSAT, DXCC, NRA
> 
> http://www.qsl.net/ke9na
> 
> "A life lived in fear is a life half lived."
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