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Re: [TowerTalk] RE : Query RFI

To: "hermans" <on4kj@skynet.be>, <WarrenWolff@aol.com>,<TOWERTALK@contesting.com>
Subject: Re: [TowerTalk] RE : Query RFI
From: "K8RI on TowerTalk" <K8RI-on-TowerTalk@tm.net>
Date: Sat, 18 Nov 2006 19:08:31 -0500
List-post: <mailto:towertalk@contesting.com>
----- Original Message ----- 
From: "hermans" <on4kj@skynet.be>
To: "'K8RI on TowerTalk'" <K8RI-on-TowerTalk@tm.net>; <WarrenWolff@aol.com>; 
<TOWERTALK@contesting.com>
Sent: Saturday, November 18, 2006 6:09 PM
Subject: [TowerTalk] RE : Query RFI

> Those who own the Math. Will tell you have a look at the FOURIER Series...
> If I remember well, a square wave generates very high pieks odd

The rise and fall times dertermine the frequency.  The wave form is composed 
of many harmonics.  The amplitude of the harmonics drops off rapidly with 
increasing frequency for a given wave form.

> harmonics.The higher the harmonic the higher the piek.

The shorter/faster the rise time the higher the frequency and number of 
harmonics that make up the wave form and thus the total energy in those 
harmonics. However as you go up in the number of harmonics the energy drops 
off with each sucessive harmonic. "I think" it drops off by the square of 
the number.  IE each sucessive one has a quarter the energy of the previous 
one...but that sounds a bit high.

This is drifiting a bit, but when it comes to light dimmers, triacs and SCRs 
(Silicon controlled rectifiers not Saturable core reactors which work much 
better but weight a bit more<G>) They vary the brightness by varying the 
point at where they turn on the switch during the AC cycle. It's a 
relatively simple circuit, but I've forgotten the name of the triggering 
device. (Diac maybe?)  Be it a triac or SCR there are only two ways of 
turning them off. They automatically turn off when the voltage wave form 
crosses zero (or rather close to it), or hitting it with a reverse voltage 
spike.  I know of none that use the second method but if you think today's 
dimmers create hash you should see what they do when forced off. <:-)) The 
turn on generates quite a spike with a fairly rapid rise time.  The turn off 
which happens just before the zero crossing, due to internal voltage drops, 
also creates a spike, but of a much smaller amplitude.

Actually these things are a treat to make and play with.  They can be a 
lesson in interactive RFI and control.  The basic units are not much more 
than a pot, diac, and triac.  The spikes generated will travel down the ac 
lines for some distance and when they find another device ... <G> they just 
might turn it on, or provided the timing is right, turn it off which 
generates even larger spikes. With three or four of them all active you may 
find turning one up, also turns another one up, but when you turn that one 
down it may affect others. So, turning some up turns others down while 
others go up.  It's much like the old Laurl and Hardy movies where they are 
being chased through a series of rooms off a hall going in one door and 
coming out of another room entirely.

The Fourrier Transform is really an infinite series of sins and cosins. In 
reality it is to some limit n where the power in the harmonic has dropped to 
an insignificant value. I'd guess more than half on TT know more about this 
than I do.

> At least fourty years ago..........hi hi

I have a math minor and it's only been 16 years but I couldn't do a 
derivative or integral if my life depended on it.  BTW my first courses in 
grad school (CS) were digital image processing and the design and analysis 
of algorithms.   The second was easy. We only went to 5 level simultaneous 
equations. By the third week in digital image processing we were doing 
fourrier transforms (not FFTs) on images. From there we moved on to matrix 
algebra...and the prof said "not much math".  Just goes to show how 
different a PHD and a lowly grad assistant view the term, "not much math". 
<:-))

Roger Halstead (K8RI and ARRL 40 year Life Member)
N833R - World's oldest Debonair CD-2
www.rogerhalstead.com
>
> Jos on4kj
>
>
>
> As Dave has already said, Dimmers do make noise. Generally they are 
> nothing
> more than a triac (bi-directional SCR) and create a terrible wave form.
>
>
>
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