[NLRS] Question on 10GHz feed

[Donn Baker]

Hi Jon,
Without seeing the feed (bring to Breakfast nextr weekend!), I'd bet small
sums of money that its for WR75 waveguide.  The window in the flange that
you see is a 1/4-wave impedeance matching plate between the WR75 and the
0.75 dia circular waveguide.  Check the spacing of the holes in the flage:
The ones parallel to the flat side of the window should be about 1.04"
apart.  The other ones are about 1.125" apart (Yes, they are not in a
square pattern!)

It will make a fine feed for 10368 GHz.

The critical dimension is the diameter of the circular waveguide.  At 0.75"
it will pass 10.368 GHz with ~3.5dB/100' of attenuation.  This compares to
WR90 at 3.2dB/100.  (WR75 is 3.75dB/100' at 10.368 GHz).

The feeds we have to drill out, the RCA DDS feeds, have a diameter of 0.66
or, which is either AT or below cutoff for propagation of 10.368GHz.

73 Donn
WA2VOI/0

At 13:03 02-12-06 EST, W0ZQ at aol.com wrote:
>
>
>I have a Chaparral feed that came with my 26"  offset dish.  Its the 
>commercial feed that was associated with the  dish.   Here is my question
- can it be 
>used for a 10.368 GHz feed  ?
>
>Here is the data:
>1.  It has a small round mounting flange (on  the transition end) which 
>doesn't seem to fit any WR90 transitions that I  have.
>2.  The window in the flange measures 0.70" x 0.49".    It is about 0.37" 
>thick (deep) where it mates up with a round  waveguide.
>3.  That round wave guide is about 2.2" long with a 0.750" in  diameter.
>4.  The feedhorn end has four or five (depending how you  count) scalar
rings 
>with each scalar ring more forward than the one behind  it.    The total 
>throat of the feed horn with scalar rings is  about 1.4" deep.   The
entire feed 
>measures about 4.25" long  end-to-end.
>
>Will this work on 10.368 GHz ?   Is that 0.70 x  0.49 flange a problem for 
>mating with standard 0.90" x 0.40" WR90 ?
>
>73,  Jon
>W0ZQ  
>
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