[NLRS] 10 GHz feed

Tue, 28 Jan 2003 17:41:33 -0500

Most feeds do not have a thick enough wall to accept being drilled for 3/4"
pipe. Bruce N2LIV

Ed Marciniak wrote:

> If one has a glutton for  punishment why not drill a hole in the casting
> large enough to accept 3/4" copper pipe with a backshort and an SMA
> connector? As an added bonus you can put a choke ring or conical horn....I'm
> thinking a 1" pipe cap drilled or a 3/4" to 1" tapered adapter
>
> ----- Original Message -----
> From: "Gerald Johnson" <[email protected]>
> To: "Jon Platt" <[email protected]>; "NLRS" <[email protected]>; "Donn
> Baker" <[email protected]>
> Sent: Sunday, January 26, 2003 7:18 PM
> Subject: Re: [NLRS] 10 GHz feed
>
> > 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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