[NLRS] 10 GHz feed

Mon, 27 Jan 2003 13:33:59 +0000

'Morning Ed.
"3/4" water pipe has an outside dia. of 0.875".  The INSIDE dia. is 0.866
for type-M (the most common) pipe.  Only when you use type-K does the i.d.
equal 3/4" (0.745, actually).  There isn't enough metal in the feed casting
to drill it out that far (0.875").

The point of using the feed that comes with the dish is that the feed comes
with the dish... you don't have to be a glutton for punishment !!  Besides,
its likely that the feed is optimized for the dish... which something we
cobble up in the basement won't be.

At 22:05 26-01-03 -0600, 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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