Re: How many joules --> e.m. waves?

[inet@intellisys.net (brian whatcott)]

At 11:47 AM 4/19/97 EDT, LUDWIK KOWALSKI wrote:

>  d(m)   L(mH)    Rohmic  f(MHz)   lambda (m)  R_rad(ohms)  effic (%)
> ------------------------------------------------------------------
>   6     0.083    0.19     0.32      943         3.1e-5      0.0167
>   2     0.028    0.063    0.55      544         3.5e-6      0.0056
>  0.6    0.0083   0.019    1.01      298         3.1e-7      0.0017
>  0.2    0.0028   0.0056   1.74      172         3.5e-8      0.00056
> 0.06    0.0008   0.0019   3.18      94.3        3.1e-9      0.00017
> ------------------------------------------------------------------
>
>                                               Ludwik Kowalski
This frequency chart reminds me that the frequencies used by Hertz in his 
early experiments were 50 to 60MHz
For a transmitter, he used a half-wave dipole of straight rods or metal 
sheets, and a central spark gap consisting of two well-polished metal balls.
 His receivers included a single turn loop with a pair of terminating balls 
in close proximity.

  And writing this reminds me of an excellent description of the next step 
in receiver technology: the Branly coherer.
 Of course you have heard of this before - but listen to this:

"Lodge found that when electrical oscillations occurred between two metallic 
surfaces in poor contact, the resistance of the contact at once fell to a 
very small amount, but was immediately restored to its original value by any 
mechanical disturbance, such as tapping. 

"Branly used for the same purpose a tube containing metal filings, and this 
was again improved by Marconi, who used a mixture of nickel and silver 
filings (95% nickel) in a small gap between two silver plugs in an exhausted 
and sealed glass tube (fig. 369).

" A battery in series with the coherer produces a sufficient current, when 
the resistance of the coherer drops, to close a relay which actuates a Morse 
inker for recording the signals."   <ref 1>


This writing was at such  a level that I felt capable of building the
receiving station described in the following figure.
 This quality of reproducibility, a prized quality I have  noted in SciAm 
issues of past decades, is (I'm sure you will agree) at the crux of the 
scientific method.

<ref 1>
Electricity & Magnetism for Degree Students,
Starling & Woodall,  Longmans

1st ed. 1912,....
7th ed. Aug 1941, 
New impressions Jan 1942, Sept 1942, Apr 1943, Aug 1944,
Mar 1945, Jan 1946, Oct 1946, Nov 1947, Nov 1948, Mar 1952.
8th ed 1953
New impression with corrections 1956.

Regards
brian whatcott <inet@intellisys.net>
Altus OK