[Elecraft] K3 - REF CAL Question

Wed Jun 18 10:15:41 EDT 2008

-40 - and the only reason I know this is that I was working in Ottawa at the
time and asked what -40 was in Fahrenheit ;-) I still can't believe I forgot
to take gloves on that trip. Fortunately, I only had to walk a couple of
blocks from the hotel to the Canadian Patent Office :-)

73,
Dave W8FGU

> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net [mailto:elecraft-
> bounces at mailman.qth.net] On Behalf Of ON4WIX
> Sent: Wednesday, June 18, 2008 2:50 AM
> To: microham at microham-usa.com; 'Lyle Johnson'; w3fpr at arrl.net
> Cc: elecraft at mailman.qth.net; Paul at N4LCD.com
> Subject: Re: [Elecraft] K3 - REF CAL Question
> 
> Let's see who first answers this one right (without looking at a
> thermometer!):
> 
> There is one point on the scale of a thermometer where the temp in °C
> equals
> the temp in F.
> Which one is that?
> Feel free to prove mathematically...
> 
> Enjoy!
> Glenn ON4WIX
> 
> ----- Original Message -----
> From: "Joe Subich, W4TV" <lists at microham-usa.com>
> To: "'Lyle Johnson'" <kk7p at wavecable.com>; <w3fpr at arrl.net>
> Cc: <elecraft at mailman.qth.net>; <Paul at N4LCD.com>
> Sent: Wednesday, June 18, 2008 12:58 AM
> Subject: RE: [Elecraft] K3 - REF CAL Question
> 
> 
> 
> 
> > F to C is much slower,
> 
> Not really ... (F - 30)/2 is generally within 10% and
> (F - 32) * 1.1 / 2 is within about 1%.  Both are easy/quick.
> 
> Unfortunately, mental math and estimation are skills that have
> been lost with the "calculator generation."
> 
> 73,
> 
>    ... Joe, W4TV
> 
> 
> 
> 
> > -----Original Message-----
> > From: elecraft-bounces at mailman.qth.net
> > [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Lyle Johnson
> > Sent: Tuesday, June 17, 2008 5:14 PM
> > To: w3fpr at arrl.net
> > Cc: elecraft at mailman.qth.net; Paul at N4LCD.com
> > Subject: Re: [Elecraft] K3 - REF CAL Question
> >
> >
> > > You have to do that with your calculator :-)
> >
> > C to F is fast and easy to do in your head.
> >
> > The "real" formula is:
> >
> > F = (1.8 * C) + 32
> >
> > My mental algorithm is:
> >
> > double the value,
> > subtract 10% (round it off, who cares if it is a degree or two off),
> > add 30,
> > then add 2 (if you feel the need for the extra precision).
> >
> > Most of us can double a number in our head pretty easily.
> > Round it to
> > the nearest 5 and then double it if you have trouble doubling
> > 37 or 43
> > or 51.  Hey! It's just the "two times" tables, which we all
> > learned well
> > before our 9th birthday.
> >
> > Doubling and then taking off 10% of the result is the same as
> > multiplying by 1.8 (or 9/5 if you prefer) but a heckuva lot
> > easier.   I
> > never did learn my "1.8 times" tables...
> >
> > Again, round it if you trip over something like 74 - 7.4.
> > The answer is
> > 66.6.  But does it really matter if you decide to subtract 10 and get
> > 64?  Or subtract 7 and get 67?
> >
> > Subtract 30 then 2 rather than 32.  Why?  Because it is easier to not
> > deal with the 1's digit until you have to.  If you feel you have to.
> >
> > I find that I can usually work it out in my head in under a
> > second and
> > get within a few degrees of the "correct" result.  Near
> > enough for most
> > needs.  If I'm tired it might take 2 or even 3 seconds to make the
> > conversion, especially if I refuse to round things off (being an
> > engineer, I sometimes get anal about numbers, which is a good
> > indicator
> > I'm tired!).
> >
> > So, for example, let's take 52C. Is the PA too hot?
> >
> > The real method:
> >
> > 2 x 52 = 104.
> > 104 - 10.4 = 94 (near enough)
> > 94 + 30 = 124
> > 124 + 2 = 126(if you really care...)
> >
> > If you'd rounded it:
> >
> >    2 x 50 = 100
> > 100 - 10 = 90
> >   90 + 30 = 120
> > 120 +  2 = 122.
> >
> > Still close enough to decide if your finals are cooking!
> > (They aren't).
> >   Would the 4 degree difference have made you change you mind
> > about the
> > safety of your PA transistors?  I doubt it.
> >
> > F to C is much slower, but I rarely have to do that :-)
> >
> > Enjoy!
> >
> > Lyle KK7P
> >
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