[Elecraft] Units

[gdaught6 at stanford.edu]

> I think the term used for the SI is "coherent," ie 1 x 1 = 1, none of your 
> dynes, cubits, foot-pounds etc.  A pity our cousins from across the water 
> are not all on board the SI express.
> 
> David
> G3UNA
> 
> 
> > On 12/8/2008 9:49 AM, Barry Garratt wrote:
> >
> >> Actually a radian is an angular measurement whereas a Hertz (hertz) is a
> >> frequency measurement.
> >>
> >> 1 radian = 57.2958 degrees
> >>
> >> 1 hertz = 1 cycle per second

etc.

One problem is that "cycles" are not really units, [nor are radians].  That is to say they 
don't HAVE units.  They are non-dimensional. F'rinstance, look at the relationship 
between the speed of light, wavelength, and frequency:

c = lf  

[I prefer "lambda" for l, and "nu" for f, but my e-mail client won't type those very 
easily]

c = speed of light in meters [or metres] per second
l = wavelength in meters
f = frequency in ????  Well, it has to be inverse seconds [sec^-1] for things to work 
out.  There aren't any "cycles" or "radians" in that frequency figure.

We physics types often use "angular frequency" instead of "frequency".  We just 
multiply f by 2pi to get angular freqency.  [It's still in inverse seconds.]  Why would 
anyone want to do that?  Look at your formulas for capacitive and inductive 
reactance for hints.

That's why it's silly to have defined the Hertz as the inverse second.  

What's even sillier is having defined inverse Ohms as Mhos.  I don't believe there 
ever was a Mr. Mho. [Mho Nomis Groeg??]

Radio is sure fun!

vy 73,



George T Daughters, K6GT
CU in the California QSO Party (CQP)
October 3-4, 2009