Re: Stupid RF newbie has a question...

From: Tim Wescott (tim_at_wescottnospamdesign.com)
Date: 10/12/04 

Date: Tue, 12 Oct 2004 13:26:11 -0700

Dave wrote:

> Well, I probably knew this at one time, but then I went into the business of
> repairing computers and associated equipment (simple troubleshooting and
> board-swapping) and did that for 12 years before sleeping for the last ten
> (with a sleep disorder). Now I find I have forgotten everything but Ohm's
> Law (and am beginning to wonder about that.) So, I have some questions...
>
> Recently bought a copy of Introduction to Radio Frequency Design (Hayward)
> and discovered just how ignorant I am now. In the first few pages there are
> a couple of symbols I don't recognize. The first is simply an ampersand (&
> symbol) but it's between a couple of variables in an equation. What is that
> called in this capacity, and where should I look to find out what it means
> (again, in this capacity.) The second is simply two vertical lines in
> parrallel, rather like the side-bars of a capital H but without the
> cross-bar in the middle. Again, what is this called and where should I look
> for information on it? (Maybe a capital pi symbol? But what does it
> *mean*?) This last reminds me of the three dots in a small triangle, used
> in logic to mean "therefore," but I don't even remember where to look to
> check out that possibility. Totally ignorant. (Shaking head.)
>
> Thanks in advance for any help. I really hate to admit being this stupid,
> but I need to know, so...
>
> Dave
> db5151@hotmail.com
>
>
What pages? What equation numbers? I don't see this is my copy ("first
ARRL edition").

The only place I know where an ampersand is used between variables is in
computer languages related to C where it means "and" (either bitwise or
logical depending on the language). A vertical bar, "|", in C means
bitwise or and two "||" mean logical or -- but that doesn't go in an RF
book!

Two vertical lines placed closely between two impedances often mean
those impedances taken in parallel, so if R1 and R2 are both 100 ohms
then R1+R2 = 200 ohms, and R1 || R2 = 50 ohms. _This_ I could believe
seeing. Pairs of vertical lines bracketing a vector quantity, ||x||
mean the vector "norm", usually the sum of the square of its elements,
but sometimes something different if the mathematician in question
notices that you seem to be understanding the material -- and I wouldn't
expect it in Hayward's book.

Three dots in a small triangle does indeed mean "therefore". Sometimes
you'll see two horizontal parallel lines with an arrowhead, like "=>",
that technically means "it follows" but is used as "therefore",
particularly on blackboards where the three dots are hard to write... 

-- 
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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