Fw: [Milsurplus] MHz Timeline???

[Mike Morrow]

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