[BC] need a NON-technical explanation

[Cowboy]

On Thursday 11 November 2010 01:48:15 pm Kevin C. Kidd CSRE/AMD wrote:
> I read somewhere (QST?) that the old meters designation originally used
> to designate frequency was applicable because the spark gap transmitter
> bandwith was extremely wide and not necessarily on a specific frequency.
>  If you got your receiver in the general area of the transmit freq it
> was easy to find.  There weren't many to choose from.

 We almost have a winner !!

 Back when I started in radio......

 The spark gap would spark, and you ran a wire to your aerial.
 To receive, you moved the wire to another, much smaller gap.
 When your friend keyed his "transmitter" and sparked his gap,
 your gap would spark in sympathy, so you could receive.
 If the aerial was the same length, the received spark would be
 much stronger, and you could communicate over a greater
 distance, say 9 or 10 blocks instead of just a few houses down
 the same street.
 The closer in length your aerial was to mine, the greater distance
 we could cover, ergo "I'm on 200 meters." 
 Anything between about 190 and 210 was fine, and didn't make
 much difference, so were considered the same frequency.
 In order to change frequency, you used a different length aerial.
 Some of us had several, to communicate with several people.
 Later, we discovered magnetic amplifiers, loose couplers, and
 such, that made it possible to "tune" the aerial without
 changing wires for several frequencies.
 A whole new world opened up at that point !!

 Much later, a guy named Alexanderson invented a generator
 that could transmit a continuous wave on one frequency only,
 so much greater accuracy was required.
 Frequency was determined by what the gear ratio was between
 the motor driving the generator, and the number of poles built
 into the generator. 
 A different method of identifying what frequency a given station
 was transmitting became required, so the number of cycles the
 generator made was used instead of just the length of the aerial.
 Somewhere around then it was discovered that a crystal could detect
 this signal without needing a spark gap to receive the signal, and was
 much more sensitive. To change transmit frequency, you changed gears
 between the motor and generator, and some of the more sophisticated
 units had a gear shift built in, but those were for the big kids, like the
 300 kilowatt generator at Tropical Radio Telegraph.
 Because the Alexanderson generated a continuous wave on only one
 very narrow frequency, one could have several conversations going
 on within the range of one aerial, so merely giving the length of the
 aerial wire became totally inadequate.
 Prior to this, things like rotary gaps gave a "tone" to the received
 signal so one could pick out different stations on the same aerial wire.
 It also allowed one to listen to a receive spark if you couldn't afford
 a crystal to tune the aerial, and pick out different stations by the
 sound of the arc.

 Hope this helps....
 It's incomplete, because my memory isn't quite what it used to be.


-- 
Cowboy