Amps
[Top] [All Lists]

[AMPS] network analysis rules!

To: <amps@contesting.com>
Subject: [AMPS] network analysis rules!
From: measures@vc.net (Rich Measures)
Date: Sat, 16 May 98 11:39:11 -0800
>.........
>i'd like to find the resistance (Re, where "e" stands for 
>equivalent, so we don't get into whether it's parallel or series, 
>nichrome or carbon, etc.) of a simple network.  i want to know the 
>value(Re) of the ONE resistor which will replace threethat are hooked 
>up as follows:
>
>there are two resistors in parallel, both of resistance R, and 
>another of the value R in series with the parallel combination.  OK?
>
>first, i would  find the equivalent of the parallel combination:  
>that means i could replace the parallel combination with a single 
>resistor of this value:
>
>Rparallelcombo = R*R/(R+R) = R/2; correct?  or, if i want, i can work 
>in "admittance space"
>
>1/Rparallelcombo=1/R + 1/R = 2/R; correct?  solve for 
>Rparallelcombo = R/2; correct?  [same answer both ways!]
>
>so far, my equivalent circuit is the original series resistor with 
>value R (remember it?) in series with a new resistor (R/2) replacing 
>the original parallel combination.  what resistor would i use to 
>replace the new series pair?...
>
>Re = R + R/2 = 3R/2 = 1.5 R, correct?  these aren't apples and 
>oranges, they are all resistors.  i took a foray into "admittance" 
>(ok, conductance) just as an optional, but not necessary, detour.  
>however i arrived at the equivalent resistance of the parallel 
>combination, i can simply treat it as a series resistor, and 
>combine it (by simple addition) with the other original series 
>resistor. 
>
>total Re = 1.5 R
>
>now the EXACT same reasoning (i.e. current is the same through 
>series elements, potential is the same across parallel elements; 
>... these are physical principles) can be used with resistors and 
>reactances.  the math is more of a pain, what with complex numbers 
>requiring "rationalization of the denominator" and stuff like that, 
>but i don't have to return to first principles every time, because 
>the equations have been solved, and they are in books!  
>
>this stuff works!  if it didn't, i couldn't "design" (with a paper 
>and pencil ... or even a computer program) any circuits.
>
Is it reasonable to conclude that the rules for DC circuits, where the 
volts and amps are always in phase, apply broadly to AC circuits, where 
the volts and amps are not always in phase?

>finally, i don't recall anyone ever saying that rich's nichrome wire 
>supressors didn't work.  they have resistance, they have 
>inductance, they even have a bit of lurking capacitance.  
>depending on the frequency, they can look just right for the job!  
>the question in my mind is whether they are always NECESSARY.
>
 Some amplifier tubes never sustain a parasitic oscillation.  Others 
apparently do.  Last night, a ham brought over three low-mileage, 
problematic 3-500Zs for testing.  One was  gassy.  The color of the 
ionized gas was that of oxygen-nitrogen, so the problem was likely a less 
than good glass/metal seal.   The other two tubes had good vacuums, 
however, they had fil/grid shorts due to bent filament helices.  .  .  
Are seatbelts always necessary? 



Rich...

R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures  


--
FAQ on WWW:               http://www.contesting.com/ampfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm

<Prev in Thread] Current Thread [Next in Thread>