Fw: [Milsurplus] MHz Timeline???

[D C (Mac) Macdonald]

The upper case "K" is used for the Kelvin temperature scale
wherein 0 is "ABSOLUTE ZERO" which is the point where all
molecular activity stops.  If I remember correctly, that is
-273 Celsius (or Centigrade as it once was called).

Therefore, 273K and 373K are the freezing and boiling points
for pure water at sea level with "standard" atmosphere.

73  ---  Mac, K2GKK/5



-- "Mike Morrow" <kk5f at earthlink.net> wrote:

Brian wrote:

>When did we phase out mc. for MHz?


I don't remember the precise dates, but the transition
was taking place in the mid-1960s in the U.S.A. with the
move to the use of S.I. units rather than English units
in science and engineering.  A 1960 conference formally
defined the S.I. unit system, including an "international"
definition of Hertz.


>Did Europe (or just Germany) always use Hertz to designate
cycles?


One Hertz  is not equal to one cycle, but rather one cycle
per second.  Our old designation was pretty sloppy, since
1 MHz might be written as 1 MC or 1 MCS or even 1 MC/S.
Only the last version was/is actually correct.

I believe the Germans have used Hz since well before WWII.

There's still a lot of sloppy usage with prefixes.
1,000,000 Hz is sometimes incorrectly written as 1 mHz or
1 mhz (which would actually be 1 milliHertz...off by a
factor of 1 U.S. billion) instead of the correct 1 MHz.

Similarly, sometimes 1,000 Hz is incorrectly written as
1 KHz (instead of the correct 1 kHz).  In S.I. units,
lower-case m (milli) indicates a factor of  0.001, while
upper-case M (mega) indicates a factor of 1,000,000.

Lower-case k (kilo) indicates a factor of 1,000.  No
upper-case K is yet used for a prefix.  Capitalization
makes a difference in S.I. units.

73,
Mike / KK5F