[NLRS] 10 ghz dish feed

[Donn - WA2VOI/0]

You don't say, but I assume you mean for the DSS feed horns converted to 10GHz, 
right ?

The basic place to start is W1GHZ's paper in Microwave Update, 1999, 
"Understanting Circular waveguide."  One caution: Figure 17 - "10GHz CIrcular 
Waveguide to Coax Transition - Best Dimentions" has an error in it.  The lables 
are BACKWARDS.  That is, what Figure 17 calls "Backsort" is actually "Probe 
length," and vice vcersa.  AND NOTE that Figure 17 is for 3/4" - M copper water 
pipe, with an inside dimention of 0.811" (not 0.75")

That said, what seems to work well with the DSS feeds is virtually the same:
Backshort distance of 0.467"
Probe length of 0.25"  (both measured off of my feeds)

The probe diameter doesn't affect things too much:  if you use a standard SMA 
connector, it will be 0.050" dia, which is just fine.

Ideally, the backshort distance is made adjustable... you can pick up a few dBs 
of return loss by optimizing the distance.

Also, try and place the probe AT LEAST one guide wavelength from the front of 
the waveguide section (where the waveguide flares into the horn).  This allows 
the undesirable modes generated at the coax transition to dampen out before they 
get presented to the dish.  For 0.75" dia guide, the distance is 2.49"  (On 
mine, the probe is back 2.566")

Hope this helps

73 Donn
WA2VOI/0


----- Original Message ----- 
From: "Marciniak, Ed" <elmarciniak at mnits.net>
To: <nlrs at mailman.qth.net>
Sent: Sunday, August 01, 2010 3:12 PM
Subject: [NLRS] 10 ghz dish feed


>
>
> Can someone point me toward a link to a drawing/template or other 
> instructions? What I’m looking for in particular would be one with probe 
> dimensions, backshort position, etc. with the WG bored out to ¾” rather than 
> the stock 0.693"
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