Fwd: Re: RE: [NLRS] 10GHz feed horn design & question

[Dr.Gerald N. Johnson]

> 
> ----- Original Message -----
> From: jcplatt1 at mmm.com [mailto:jcplatt1 at mmm.com]
> Sent: 11/29/2004 1:14:43 PM
> To: Donn.Baker at UNISYS.com
> Cc: nlrs at mailman.qth.net
> Subject: RE: [NLRS] 10GHz feed horn design & question
> > 
> > Thanks for the excellent feedback Donn.   I may go ahead and build a new
> > feedhorn, heck its Winter anyway.
> > 
> > Regarding the focal point, the good news for this dish is that the feed-arm
> > positions the feed so the only adjustment is in (closer to the dish) or out
> > (farther from the dish)--  I assume along the axis of the focal point (??
> > note to self -- something to check).
> > 
> Depending on the horn parameters, the best place for the focus isn't necessarily at the plane of the mouth of the horn, but may be a bit inside. The only way to be sure of the best point is by gain or pattern.
> 
> > Regarding building horns (feed or otherwise), I am looking for input from
> > other horn-builders regarding the following.
> > 
> > 1.   What material do they use for the horn itself ?    Cutting and bending
> > is the issue (brass vs copper, and at what thickness).
> 
> Brass and copper both work, as does copper clad PC board. Remember the skin depth is small. Bending need not be the limit, soldering may be the limit to make the corners. I've used near copper foil, but the horn can be a bit fragile.
> 
> > 
> > 2.   Because the horn bends in on it self, its hard to get a sharp corner
> > -- you can't get a brake in on all the bends.    I think AUS mentioned
> > that he built a jig ?   I think this issue works in concert with my
> > question #1 above.
> 
> You could carve a block of hardwood to the shape of the inside and push the copper against that.
> 
> > 
> > 3.   What do others use for a mounting flange and with what material.    I
> > suppose that you can home-brew a small flange with a .400" x .900" opening
> > with standard home tools.
> 
> You can homebrew a flange or buy a flange or start with a piece of waveguide with a flange.
> 
> > 
> > I've noted with some interests the aluminiumized (??) plastic used by
> > M/ACom for their 17 dB horns -- lightweight and strong.    There is no
> > reason that the horn has to be brass or copper.   For example, can you
> > build a horn out of a non-ferrous material (cardboard, wood, plastic, etc)
> > then give it a good coating with silver spray paint on the inside assuring
> > that all seams are indeed covered (no gaps) ?    Another version of this
> > may be to use aluminum foil to line the inside of a non-conducting horn
> > -- the advantage being it may be easier to work with these materials.
> 
> The losses go up with the silver paint and with poor conductivity at the corners. You would have most troubles with aluminum foil unless you cut the foil to have the seam(s) along the minimum current line, the middle of the broad sides.
> 
> As far as I can tell, the only reason for having sharp corners is that they make a nice looking transisiton to the sharp corners of the standard waveguide. Otherwise rounded corners or a round horn works just fine. Generally for a dish feed you want a different height than width to get a symmetrical pattern, otherwise a circular horn can be used and is often used. At 10 Ghz a good horn starts with a 1-1/2 to 3/4" copper fitting.
> 
> 73, Jerry, K0CQ
> Dr. Gerald N. Johnson, Electrical Engineer
> > 
> > 73, Jon
> > W0ZQ
> > 
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