[NLRS] Waveguide transitions

[John P. Toscano]

Although Lenny (K0SHF) is working on getting me an LNB drilled out and 
an SMA connector added to serve as a feed for my offset dish on 10.368 
GHz, I have also been looking around for a waveguide to coax adapter on 
eBay without much success.

I did find a couple of postings of waveguide to SMA adapters that don't 
specify a waveguide type/size, but say only that the waveguide opening 
is approximately 3/4" wide by 3/8" high (that would be 0.750" x 0.875") 
in one case, and 1/2" x 1" in another case (0.500" x 1.000"), and 3/8" x 
7/8" in yet another (0.875" x 0.375")

The dimensions of WR-90 are allegedly 0.900" x 0.400" while WR-75 is 
supposed to be 0.750" x 0.375".  I say "supposed to be" and "allegedly" 
because my only source for the dimensions of waveguide is a web site 
found by google:  http://www.wa1mba.org/wavegd.htm  and I have not taken 
the time to find a more definitive source, but it's probably right...

Anyone know if these surplus waveguide adapters would work @ 10.368 GHz, 
since they don't seem to be either WR-75 or WR-90?  In particular, two 
of these surplus waveguide transitions seem to have a very different 
width-to-height ratio than either WR-90 or WR-75, although the third one 
I mentioned is pretty close to falling between WR-75 and WR-90 in 
dimensions so I imagine it should work.

One of my thoughts was to build a horn on the adapter, in fact, I even 
thought it might be interesting to try building a horn in 2 or 3 
sections that could be stacked according to how much gain vs how much 
beamwidth you wanted in a given situation, and maybe point that forward 
(away from the dish) with a coax relay to select either the low-gain 
horn for easier pointing at strong signals or the full dish for 
high-gain at the expense of more difficult pointing.  Of course, this is 
probably more effort than the idea deserves, but if only time was not in 
such short supply for me, I'd love to play around with it, even if it 
only taught me once again to KISS (Keep It Simple, Stupid!).

And while I have the attention of some 10 GHz experts, I'm wondering if 
you have any words of wisdom about the jumper from the transverter to 
the adapter.  I have some pieces of RG-58 (ugh), RG-142, and LMR-200 
(all of them are RG-58 size) to which I can easily attach SMA male 
connectors.  But the losses at 10GHz for any of them seem awfully high. 
  I looked at the Times Microwave site and found a description of some 
coax called LMR-240LLPL (Low Loss Plenum) and they make SMA males for 
that stuff.  It has noticeably less loss than ordinary LMR-240 and, of 
course, better loss figures than LMR-200 or RG-58.  Of course, it is 
hard to find.  Radio City said they'd special order it, but the list 
price is $4.75 a foot, so if I went that route, I certainly wouldn't be 
buying up a whole spool (hundreds of feet) and using it around the shack 
for other jumpers at more modest frequencies!

I suppose I shouldn't worry about that either.  We're talking about 
losses (dB/foot) in the range of:

   RG-58.................... 0.582
   RG-142................... 0.499
   LMR-200 Ultraflex........ 0.431
   LMR-200.................. 0.361
   LMR-240 Ultraflex........ 0.334
   LMR-240.................. 0.281
   LMR-240 LLPL............. 0.272

A pair of SMA connectors will probably add more loss than any of these 
coax cables, at least for a short run.  And the transverter WILL be 
pretty close to the feed horn.  I guess I am more worried about the 
degradation of NF than the amount of reduction in transmitted power, 
since I have one of the new DEMI "2 watt" units.

P.S., congrats on all the fun you guys have been having on rain scatter, 
I'm getting jealous!  My system hasn't even had power applied to it (by 
me, at least).

73 de W0JT