[NLRS] 10 GHz feed

Mon, 27 Jan 2003 13:23:49 +0000

Hi Jerry,

I think you still have to do some surgery on the interior.  The Sony feed
has a  fin running about 2/3 the length to separate the H and V components.
 As I remember it, there wasn't room enough to slide a dielectric slab into
the guide.

I had no trouble drilling out the guide to 3/4".  There was enough metal
left that I was able to use 1/8" 2-56 machine screws to mount an SMA
connector directly to the outside.  The 2-56 was flush with the inside of
the wall.

73 Donn
WA2VOI/0

At 19:18 26-01-03 -0600, Gerald Johnson wrote:
>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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