[NLRS] 10 GHz feed

[Donn Baker]

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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