RE: IML: Is this the "MultiPlex"?

["Dick Benjamin" <dickb@xxxxxxxxx>]

In the 1980's, car radios became available using "Quartz lock" technology,
which most of you will recognize by the digital readout dial.  This is a
technology which takes away all the problems of drift and tuning errors,
because the radio has an internal standard clock which is slaved to the
physical size of a very small quartz crystal.  

The radio's tuning frequency is synthesized by digitally multiplying the
quartz resonance frequency by whatever multiple is required to tune each
particular channel frequency.  These radios have a notchy feel to the tuning
knob, and a digital readout which jumps (usually by .2 MHz) per click on FM,
and 10KHz per click on AM.  There is no drift or temperature variation, or
sensitivity to vibration or voltage level.  This was an enormous improvement
in performance. 

Independent of that, but at about the same time, the geniuses of EEdom
developed the "phase lock loop" type of detector, which has a "capture"
effect.  In layman terms, this means that once a station is tuned in, the
radio will tend to reject all interfering signals, EVEN THOSE ON THE SAME
CHANNEL!, with the result that even in weak signal conditions, FM Stereo
reception with at least 30 db of quieting is now common - leading to almost
perfect reception right up to the point of just about zero signal strength.


Further, at about that time, there came into common use very cheaply
available ultra low noise level "front end" RF amplifiers, which are able to
pull out of the atmospheric background noise signals that are hundreds of
time weaker than that needed by the older technology receivers.

This technology was developed under government research contracts which were
originally let for space exploration and military reconnaissance hardware,
which was of course classified for many years.  It is one of the really
wonderful byproducts of the nation's quest into space (and of the cold war)
which we enjoy now.  I was somewhat involved in these developments, at MIT,
UCLA and TRW in the 50's and 60s, and those who worked very hard in that
field are gratified to see the widespread benefits it has now brought to
everyone's life.  So it wasn't all $600 toilet seats!

Dick Benjamin

  
-----Original Message-----
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Sent: Monday, January 17, 2005 11:59 AM
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Subject: RE: IML: Is this the "MultiPlex"?

Quoting Dick Benjamin <dickb@xxxxxxxxx>:


> Be aware, that while the sound is superb from this setup, it is only good
> for in town use.  The radio is 60's technology, it is no where near as
> capable of pulling in distant stations and staying locked on to them as
you
> are all used to with modern radios.

Dick, my multiplex will stay tuned about 50-60 miles away from town.  Modern
cars that I have driven do not do much better.  The only problem I have is
when
I cross power lines that carry a lot of wiring.  Then, the poor thing gets
confused and play several stations simultaneously.

D^2



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