Author Topic: The Work of Jagadis Chandra Bose  (Read 2436 times)

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Offline Zero999

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The Work of Jagadis Chandra Bose
« on: November 09, 2014, 06:45:55 pm »
I've just found this article about Jagadis Chandra Bose. It's amazing he was experimenting with microwaves in the 60GHz region and semiconductors way back in the 1890s!
https://www.cv.nrao.edu/~demerson/bose/bose.html
 

Offline Zero999

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Re: The Work of Jagadis Chandra Bose
« Reply #1 on: November 23, 2014, 11:11:01 pm »
wow ... the sugar polarizer !
I don't believe he used sugar to polarise microwaves. He experimented with using jute (dielectric substance) to polarise microwaves, in a similar manner to a sugar polariser at optical frequencies.

I wonder how easy it is to do this kind of thing as a hobbyist?

He uses a spark gap to produce the microwaves but how is it tuned? Perhaps the sphere act as a resonator?


The receiver looks just as interesting, perhaps a biased diode connected to as suitable antenna would work?
 

Offline T3sl4co1l

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Re: The Work of Jagadis Chandra Bose
« Reply #2 on: November 24, 2014, 01:46:55 am »
Sparks produce truly wideband noise; I didn't think it went much into the GHz, but it would seem so!

Still reading, looks pertinent: http://www.ece.unm.edu/summa/notes/SwN/SwN28.pdf

There will be some effect from the electrode shape (corona priming the gap, self capacitance of the immediate structures -- or really, the characteristic impedance of them as the spark wave propagates over them), but once you have the energy at whatever frequency you want, you just tune it to select a frequency.  Spark gap transmitters have always been notoriously noisy, both in repeat rate (except for a few CW methods, which were probably still very hissy, but could at least accommodate intelligible voice) and bandwidth (without careful filtering between generator and antenna, expect bandwidth as a sizable percentage of center frequency -- not to mention harmonics!).

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
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Offline Zero999

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Re: The Work of Jagadis Chandra Bose
« Reply #3 on: November 24, 2014, 04:35:55 pm »
It appears most of the early research into millimetre waves involved the use of spark gap transmitters.

Here's more information I've found:
http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1925ApJ....61...17N&db_key=AST&page_ind=1&plate_select=NO&data_type=GIF&type=SCREEN_GIF&classic=YES
http://www.dtic.mil/docs/citations/AD0620727

Arcs seem to produce radiation all the way from RF to light. Mercury arc lamps also produce significant radiation in the 120 GHz - 6THz.
http://en.wikipedia.org/wiki/Mercury-vapor_lamp#Molecular_spectroscopy

It'd be interesting to experiment with this.
 


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