[NLRS] 10 GHz feed

Sun, 26 Jan 2003 19:18:08 -0600

Or stuff the guide with a dielectric, such as polystyrene foam, teflon foam, or solid teflon. That should be easier than drilling to a diameter larger than the outside diameter of the casting.

Probably with solid teflon only a bar say 1/4" wide down the middle would be enough. Make if full waveguide height.

73, Jerry, K0CQ

---------- Original Message ----------------------------------
From: Donn Baker <[email protected]>
Date:  Mon, 27 Jan 2003 01:10:58 +0000

>Hi Jon,
>Using the existing feed will make life a lot easier.  Although its designed
>for 13-14 GHz, it should work at 10GHz MAYBE.
>
>The Chaparral feed should be OK... not optimal, maybe, but they work well.
>Gary, W0GHZ, has two (I think) of the original feeds on Sony DSS dishes.
>They work just fine.  I'm using one on my WBFM gear.
>
>The thing that does have to be done, though, is to cleanout, and maybe bore
>out , the circular waveguide section.  Its possible that the walls are not
>thick enough.  The Sony ones are ~0.63" I.D.  This will NOT propagate
>10.368 GHZ in TE11 mode.  Both Gary and I bored the section to 0.75"
>(convienent drill size).  0.75 has a TE11 cutoff of 9.22GHz.  Works great
>at 10.368 (or 10.230GHz) even though the guide wavelength is starting to
>get long.  If the wall thickness won't support 0.75, the smallest I'd go is
>23/32, or 0.71875.  That's a special drill, however, and may be hard to
>find.  
>
>My reason for that silly number ?  The guide wavelength (Lambda-g - Lg) is
>starting to get long at 0.75" (2.49" vs 1.28" free space - L0).  It goes up
>exponentially: at 0.7" Lg is 3.058", and at 45/64 or 0.703125" its 3.603".
>Losses go up with the guide wavelength.
>
>Mating to the somewhat odd-ball flange isn't really a problem.  You can
>just butt a standard (WR90 or WR75) flange to it with acceptable losses.  A
>transition is better, of course.  The 0.7 X 0.48 has a cutoff of 8.34GHz,
>so that's not a problem.
>
>Transitions are not really a problem... at least at 10GHz.  Just a little
>bending and such with some brass or copper sheet.
>
>Good luck.
>
>73 Donn
>WA2VOI/0
>
>
>At 17:29 26-01-03 -0600, Jon Platt wrote:
>>I have an offset dish that I salvaged from my neighbors garbage pile
>during last Falls clean-up days here in Bloomington.   This dish is fairly
>flat, offset, and measures about 24" x 26" or so.  My question is the feed
>that came with it.   The flange end of the feed measures 0.70" by 0.48" and
>doesn't seem to conform to WR90 or WR75 waveguide ... its close to WR75
>(0.75 x 0.38)   The flange end transitions into a round tube about 4" long
>with the same 0.480" diameter.  The non-flage end is scalar like with five
>or six rings .... the whole feed is about 4.35" long.
>>
>>Questions:  Anyone have any clue as to if this feed may work on 10368 MHz
>and is so, how or what transition to put on the flange end ?
>>
>>73, Jon
>>W0ZQ
>>
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