[MAMS] 47 GHz

[Dr. Gerald N. Johnson]

Sometimes its more productive to order and get next day delivery than to 
drive 23 miles one way to the nearest hardware store, then hobby stores, 
that carry K&S to find them out of stock. Though the delivery costs from 
McMaster are higher this year than they used to be.

So long as the ratio of width to heights are the same different sizes of 
wave guide can be butted without a serious mismatch. The Z0 is based on 
the ratio of height to width. The junction will impose a lumped C across 
the guide that usually isn't all that bad a mismatch.

Must tell a tale.

Iook a senior/grad Fields Course as a beginning master's candidate. 
About half seniors and half grad students. It was taught by a professor 
experienced in physical chemistry, but not electrical engineering. He 
thought since it was based mostly on 3D tensor analysis that he knew 
enough of that. It was a 4 quarter course, I have notes from the first 
quarter, but none after that. It proved that he was reading enough per 
class day to build a lecture on expanding the math but had never read 
the book to the end. One day after spending about a week developing the 
relations for a step in a waveguide height, one student named Charlie 
Sie spoke and asked, "Professor K...., what's this good for?" Professor 
K.... looked at me and knew I had industry experience and said, 
"Johnson, what's this good for?" Rather that coming off the top of my 
head knowing it made a mismatch from the capacitance across the guide 
and was also used as an element in making filters, I had read ahead in 
the book and quickly thumbed back to the filter chapter and said, "Back 
on page 455, our book author (R. F. Harrington) uses them to make 
filters." The professor looked like I'd inserted a knife between his 
ribs and twisted it. He deserved it.

Charlie went to Ovonics in Michigan, a pioneer in polycrystaline solar 
cells. I got drafted. The professor continued muddling his way through 
courses he didn't know anything about.

73, Jerry, K0CQ

On 10/31/2011 10:11 AM, Zack Widup wrote:
> Yeah, I looked at their selection. For my purposes 1 foot of the
> rectangular bras tubing was plenty. I did get the aluminum stock from
> McMaster-Carr and it was delivered the day after I ordered it.
>
> Probably for the circular waveguide the nearest English unit size of brass
> tubing (also available in most of the hardware stores around here) will do.
> Since these transverters I'm making are one-up assemblies and don't have to
> mate with anything commercial, they should do fine. One of the joys of ham
> radio.
>
> 73, Zack W9SZ
>