[ARC5] The International System of Units (SI)

[Leslie Smith]

Hello Bill,
My original posting (mHz vs MHz) began when I tried to understand how
the value of the low-band coil in the BC-221 could have an inductance of
only 10.4 microHenries.  The parts list I got from 'the web' said that,
but it was wrong.  From experience I knew 10.4uH was appropriate for 160
or 80 meters, not a frequency below 300kHz.   Chasing this point, I read
the manual for the BC-221, where I saw the correct value was 10.4
milliHenries, as wrote earlier.  Here is an example where some-one
confused mH and uH.  So I wrote that the confusion between mHz and MHz
was one of my pet peeves.  Except this time it was mH and uH.  

I think this quest for precision can be a point of great interest for
some and frustration for others.  Practical types say,  "The meaning is
obvious - that's the only communication I need."  The opposite
personality takes delight in precision for precision's own sake.  

In Tasmania (VK7 is a small island south of the Australian mainland) a
group has been experimenting with long range optical communication.  At
first their goal was kilometers.  Next they got communication (by light)
from Hobart to Launceston.  That's about 120 miles.   That's pretty
cool, in my book. At the same time it was quite pointless.  When I was a
child, my neighbour, (VK7ZAS) could point his 2 meter beam in the
general direction of Launceston and get instant communication. 
Easy-peasy.  BTW - his home-brew 2 meter transmitter put out thing like
one watt.  Geoff didn't need to cart a car-load of gear to the top of Mt
Wellington (higher and out of the smog).  He only had to to turn his
beam in the "general direction" of Launceston.

Returning to the precision of long-distance communication by light -
Last time I read about this group they planned to communicate across
Bass Straight - about 300 miles.   If they make the distance - that will
be super-cool.  Super-cool but pointless.   Anyone can get across Bass
Straight on 80m (or 40m during daylight hours).

If the group get optical comms over that distance - it will clearly be
an achievement worth some praise.   That brings me the full circle. 
There is a place for practical fellows and for the fanatical
"milli-Hertz" precisionists.   My interest in the value of the coil in
the BC-221 was entirely practical.  I want to do "something" with a
trashed BC-221.  Luckily for my project, my intuition that 10.4
microHenries "does not resonate" at 125 or 200kHz led me to understand
the nature of the uH vs mH problem.

But I understand your experience in the Navy has already taught you the
importance of precise communication.
Military types understand that.


   73 to you de Les
   vk2bcu at operamail.com

On Mon, Feb 15, 2016, at 22:06, Bill Cromwell wrote:
> Hi,
> 
> This topic has spread out across a couple of threads. I have started 
> using the 'long form' more just because of the ambiguity. Newer hams 
> seem to be more easily confused and I suppose that is to be expected. 
> Somebody in one of the threads mentions the notes on schematics that 
> defined the units and their abbreviations as used in the schematic. That 
> tickled my own memory of how I became aware something more than a couple 
> of weeks ago.
> 
> Milliherz are used by the WSPR and some of the other "takes all night 
> for a callsign" crowd. It's not that they actually use a signal 
> frequency of 1 or 2 millihertz but that they resolve frequencies to the 
> nearest milliherz or fraction thereof. My hat's off to them but 
> frequency measurement and control to that degree is it's own reward and 
> is a waste of time for me the way I practice the hobby. All night to 
> exchange a callsign? Harumph..
> 
> 73,
> 
> Bill  KU8H
> 
> 
> 
> On 02/14/2016 09:57 PM, Bart Lee wrote:
> > In Emergency Services, we now have to speak plain language. All of 
> > these abbreviations (and many others, especially in the law and 
> > scholarship) came about when type and type setting was expensive. 
> > Because of all the lurking ambiguities in abbreviations, even official 
> > ones, I try to write in plain language and spell everything out (even 
> > for sophisticated readers, at least at first). Our "WordProcessors" 
> > make this easy to do, throughout a note or even big document. The 
> > extra electrons don't mind. Readers may appreciate it.
> >
> > Reading confused and confusing old diagrams is another issue...
> >
> > 73
> >
> > ##
> >
> > -- --
> > Bart Lee,
> > Attorney at Law
> > Office Phone 415 956 5959 x203
> > Office Fax Line 415 362 1431
> > Cell Phone 415 902 7168
> > Snail Mail: 388 Market St #900
> > San Francisco, CA 94111-5311
> > www.bartlee.com <http://www.bartlee.com>
> >
> >
> 
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