[ARC5] An apology for a joke gone completely wrong

[Leslie Smith]

  Hello Richard,
  I must apologize profusely.  I KNOW you'd never spread
  mis-information, nor be a "nasty" type.
  That is obvious from our previous correspondence and shared interests.

  Here, in Australia, we have a curious form of humour based on an
  emphasis of the non-existant.
  
  So - for example - recently a New Zealander - a friend of mine - wrote
  that Australian's were so dangerous that NZ dug a 2000 km moat around
  their country (the Tasman Sea) and filled it with sharks - just to
  keep the Australian's away.  But this sort of joke means we are both
  friends - except on the football field.  On the football field - it's
  war!  Nothing less.

As for the impedance of power station generators - yes this a good
example to illustrate the theorem, "maximum power transfer theorem"  -
(mptt).
 I remember our physics lecturer, (Dr Laurie Draper) used the same
 example to illustrate that the theorem can be easily misapplied.  

Your second example, where the aim is to illustrate the importance of
transferring a signal with minimum noise is useful, and how the use of
the max power transfer theorem can lead to poor conclusion.
If the input "Z" is high, we should "aim" for maximum signal voltage,
not maximum power transfer.
That's what I understand.

An analogous type of misunderstanding (but nothing to do with mptt) can
occur when designing small signal amplifiers.
Normally the design puts the collector (or anode) voltage at half the
supply.
This is essential where the signal swing is large.
If the signal swing will never drive the device (valve or transistor)
into saturation (i.e. clip the signal) more gain can be had by using a
higher load impedance.
This will give more gain.


  73 de Les Smith
  vk2bcu at operamail.com


On Wed, Oct 22, 2014, at 03:37, Richard Knoppow wrote:
> 
> ----- Original Message ----- 
> From: "Leslie Smith" <vk2bcu at operamail.com>
> To: "ARC-5 List" <arc5 at mailman.qth.net>
> Sent: Monday, October 20, 2014 12:14 PM
> Subject: [ARC5] The maximum power transfer theorem. [Was: 
> Receiver inputimpedance...)
> 
> 
> >  Hello Richard,
> >  After reading your last posting, below, I'm trying to 
> > figure whether
> >  you're a nice bloke (informative) or a nasty bloke 
> > (giving
> >  mis-information)!
>    If there is misinformation its from my misunderstanding 
> not being nasty. Power stations try to operate as nearly as 
> possible with a source impedance of zero specifically so 
> that a minimum amount of power is dissipated in the 
> generator. Of course there are losses in the distribution 
> but that is incidental. Equipment running on the power line 
> does not have any sort of specific impedance, rather its 
> determined by the amount of power the thing is supposed to 
> absorb. Thus light bulbs (incandescent types) have a hot 
> resistance which varies with the power rating of the lamp.
>     I think the conditions for antennas is much like that 
> for microphones where the microphone has is the source and 
> has a rated impedance and the sink is the pre-amplifier 
> which is designed to have as good a signal to noise ratio as 
> possible along with its other properties.
> 
> 
> --
> Richard Knoppow
> Los Angeles
> WB6KBL
> dickburk at ix.netcom.com 
> 

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