[NLRS] Waveguide transitions

[John P. Toscano]

Donn (and Doug and Jon and others too!), thanks for taking the time to 
answer my questions and in the process of illuminating some dark 
corners, making me even more aware of what I don't know in this arena. 
I hope you won't mind a few more followup questions.  And since I know 
I'm not the only 10 GHz rookie on this list, I figured it would be okay 
to send the questions back to the whole list instead of just to you.

Baker, Donn B wrote:
>>One of my thoughts was to build a horn on the adapter, in 
> 
> Two different things... a transition, and a horn.  Both will have flanges. 

Do I have my terminology wrong?  My (mis?-)understanding was that the 
transition was the piece of hardware that converts from waveguide to 
coax, and that to make a horn feed, I would go to the W1GHZ web site and 
get the program that draws a horn template, transfer it to a sheet of 
brass, cut, bend/fold, and (NOT staple, spindle or mutiliate) but solder 
the sheet of brass into a 3-dimensional horn, and attach that to the 
waveguide end of the transition to make a feed horn.  I guess I don't 
understand your comment, so can you tell me what you meant by it?  Just 
trying to understand as much as I can here...

> With strong signals, you DON'T NEED easier pointing !!  (KISS!)

OK, I am willing to take your word for it, and will KISS off my failed 
eBay bids on transitions and stick with the dish feed that Lenny has 
gotten modified for me (and one of these days, get out of work at a 
reasonable hour and drive the 2 miles or so from there to his place to 
get things put together with his help).  P.S., thanks in advance, Lenny!

> Jon pointed out ".141" as the cable to use.  Correct.  And, use AS
 > SHORT A RUN AS POSSIBLE.  Mount the TR switch/Transverter/etc., UNDER
 > the feed arm of the dish, and use 3-6" of cable to go from the TR
 > switch to the feed.

 From Doug's earlier comments, I'm starting to think that maybe I should 
remove the two 90 degree SMA elbows from the T/R relay also, even though 
they were factory installed by DEMI and I would hope that they are aware 
of how easy it is to introduce loss at 10 GHz.  I see that some folks 
have done this, and some haven't.  I was planning to mount the 
transverter as you describe in one manner or another, but now I'm 
thinking that the existing 90 degree elbows may be a problem (even if 
they are pre-fabricated SMA-to-SMA elbows installed by DEMI).  Perhaps 
two straight pieces of ".141" with an SMA connector on each end (instead 
of an SMA barrel adapter) to move the relay out a couple of inches from 
the transverter and horizontal, so that the common lead could come away 
from the relay with a very gradual curve over to the feedhorn.  This 
thought comes mainly from Doug's comments about his problems with this 
part of his system, and a comment at the last breakfast from Bob that 
he's never seen a 2-watt DEMI unit that actually put out 2 watts.  Maybe 
there's close to 2 watts at the transmit port, but too much loss at the 
output of the T/R relay due to the elbows...

As it turns out, I already have about 3 feet or so of Semi-rigid 0.141" 
that I picked up at Aurora several years ago for an unrelated project 
that never went anywhere, so I guess I only need to scare up some SMA 
males for it.

It looks like Digi-Key has some at $5.62 and $3.99 each, and DEMI has 
some that are $1.50 each.  The ones from DEMI (Johnson 142-0694-016) use 
the center conductor of the semirigid without any sort of pin as the 
central contact, although the catalog page that their site points to 
mentions a different part number that also has a center pin (which I 
presume DEMI doesn't normally stock).  I don't know for sure which style 
Digi-Key sells, but from the drawing I *THINK* they have a separate 
center pin.  Any words of wisdom on the choice of SMA's for .141 semirigid?

   http://dkc3.digikey.com/PDF/T042/0232.pdf
   http://www.downeastmicrowave.com/PDF/smass.pdf


> A good thing to do (my opinion) is find some pre-made SMA - .141
 > "jumpers" FIRST, and THEN plan the layout of the transverter/dish
 > mounting, etc.

Sounds reasonable, but now THREE of you have said that sharp bends are 
bad, and sharp bends followed by an attempt to straighten out the stuff 
are still bad.  So I guess I am a bit leery of buying some pre-made 
jumpers of questionable history, given my limited resources for testing 
them.

Again, thanks for the helpful hints so far.  I really appreciate all the 
help I get from the folks on the reflector.

P.S., I have a spot picked out for working the Friday PM 10 GHz net. 
It's in Eagan, very close to my place in Apple Valley.  Its only claims 
to fame are (1) close to where I live and (2) a clear shot at downtown 
Minneapolis (easy to see the buildings) :) but pretty nearly completely 
obstructed to everything else.  :(    But, the way my work schedule is 
going, it doesn't look like I'll get stuff ready by THIS weekend.

73 de W0JT