[ARC5] The International System of Units (SI)

Mon Feb 15 15:05:56 EST 2016

     Perhaps its the medium is the message, light can carry messages for 
enormous distances but only when contained or conducted in a 
non-diffusing medium like optical glass. I am reminded of articles in 
experimenter magazines when I was a kid showing how to build a 
photo-electric link to communicate over short distances such as to a 
friend in a nearby house.  I never tried it. I suppose one could 
consider morse via flashlight as part of this.  I think the folks doing 
this are having a wonderful adventure.

On 2/15/2016 11:52 AM, Leslie Smith wrote:
> 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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-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL

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