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Author Topic: Destructive Interference in Radio (Hertzian) Waves  (Read 3803 times)

Offline jjibex

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Who was the first on record to discover "destructive interference" in radio waves (what was formerly called "Hertzian" waves)? ...When, where, and how?


 

Offline syhprum

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Re: Destructive Interference in Radio (Hertzian) Waves
« Reply #1 on: 16/07/2012 20:09:29 »
Although H.Hertz himself demonstrated much phenomena with radio waves he used spark transmitters which generate a wide range of frequencys so that I don't think any destructive interference effects woud have been noticed.
It was probably later when contiuous wave sources were available that they would have been seen perhaps by Amstrong or Telsa or one of the researchers of this period.
 

Offline jjibex

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Re: Destructive Interference in Radio (Hertzian) Waves
« Reply #2 on: 16/07/2012 22:36:44 »
Hard to pinpoint this information... In light of the "Maskelyne affiar" of 1903, as described by Sungook Hong in his book "Wirless:From Marcon's Black Box to the Audion" ( newbielink:http://mitpress.mit.edu/catalog/item/default.asp?ttype=2&tid=8638 [nonactive]), it would appear interference was used at that time, thus it must have been known previously. But who first discovered the phenomena, where, when, and how... the question remains.
 

Offline Soul Surfer

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Re: Destructive Interference in Radio (Hertzian) Waves
« Reply #3 on: 16/07/2012 23:54:32 »
It was known and understood a a property of waves using sound and water from well before the discovery of electromagnetic waves.  Its detection in light indicated that light was in fact a wave again before the full understanding of electromagnetic waves so it was not really discovered it was known that this would happen before experimentation in radio waves started.
 

Offline jjibex

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Re: Destructive Interference in Radio (Hertzian) Waves
« Reply #4 on: 17/07/2012 00:21:58 »
...useful reply, indeed, it makes logical sense... Still, was there some scientist who may have openly theorized or perhaps demonstrated "destructive interference" in radio waves (called "Hertzian waves" after Hertz and until they were later called "radio waves"), either prior to or after Hertz? ...Faraday, Maxwell, et al. ??? Would love to get some concrete info here. Thanks!
« Last Edit: 17/07/2012 04:02:11 by jjibex »
 

Offline Soul Surfer

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Re: Destructive Interference in Radio (Hertzian) Waves
« Reply #5 on: 17/07/2012 08:47:55 »
"beats",  periodic constructive and destructive interference in sound waves from strings tuned closely together in frequency have been known to musicians since before recorded history.  Kundt showed it in sound waves in 1866 but that is just an apparatus to show what he already knew would happen.   The scientist who probably described it first in a scientific way was Young in the early 1800s with his classic two slit interference experiments with light.
« Last Edit: 17/07/2012 08:49:34 by Soul Surfer »
 

Offline jjibex

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Re: Destructive Interference in Radio (Hertzian) Waves
« Reply #6 on: 17/07/2012 15:02:24 »
It's extremely helpful to know that interference had been observed in light, sound, and water at a much earlier time, that certainly establishes the theoretical basis for it in radio ("Hertzian") waves.... That said, was there someone who actually demonstrated the physical phenomena of destructive interference in radio waves prior to the Maskelyne Affair of 1903 as described by Sungook Hong in his book "Wireless" - if so, who was the first, when, where, and how?
« Last Edit: 17/07/2012 15:08:53 by jjibex »
 

Offline syhprum

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Re: Destructive Interference in Radio (Hertzian) Waves
« Reply #7 on: 17/07/2012 20:42:02 »
I think we must be careful to understand the meaning of interference, what Maskelyne did was disrupt a demonstration given by the Marconi company what we are discussing in this correspondence is the physical interference between two source of radio waves of the same frequency that results in peaks and nulls in field strength.
This can often be observed in areas served by two synchronised medium wave transmitters where in well defined spots the signal disappears. 
 

Offline jjibex

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Re: Destructive Interference in Radio (Hertzian) Waves
« Reply #8 on: 17/07/2012 21:00:18 »
My understanding from reading Hong's book was that Maskelyne did indeed use the physical phenomena of destructive interference in 1903, but perhaps I misread it. If there is information suggesting otherwise I would be very curious... But my broader question still remains, who was the first to demonstrate the physical phenomena of destructive interference in radio waves (not merely theorize), and what were the circumstances?
 

Offline yor_on

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Re: Destructive Interference in Radio (Hertzian) Waves
« Reply #9 on: 18/07/2012 01:35:16 »
Why is this important?

Take a look at the Catalogue of the Marconi Archives. "letter from H. Cuthbert Hall to Marconi, reporting on difficulties encountered in reporting the 1901 Americas Cup Yacht Race owing to interference from rival companies, 1901."

And Newton experimented with it too it seems, although not thinking of it as 'waves', instead preferring particles/corpuscles. Practically seen I think a lot of people expected it to exist as soon as they started to think of it in form of waves. Or just experiment with radio, finding it to be a certain way.
 

Offline jjibex

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Re: Destructive Interference in Radio (Hertzian) Waves
« Reply #10 on: 18/07/2012 04:18:19 »
Very useful information... unfortunately there doesn't appear to be a hyperlink for the "letter from H. Cuthbert Hall to Marconi..." so it might require a trip to Oxford to read it (which probably won't happen anytime soon), but thank you! ...I'm doing a lot of reading and research in this area lately and I'm surprised and curious to find that this information is not readily known. I suspect in the early 1890's there may have been some experiments following Hertz's discoveries, but I haven't been able to confirm that yet... So 1901 is the earliest date so far for "destructive interference" in observed radio wave phenomena, but does it go back further?
 

Offline syhprum

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Re: Destructive Interference in Radio (Hertzian) Waves
« Reply #11 on: 18/07/2012 05:47:07 »
There could have been no observation of destructive interference in the technical sense until continuous wave transmitters were available, up until WW1 virtually all communications used relatively broadband spark transmitters where it just does not occur.
 

Offline jjibex

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Re: Destructive Interference in Radio (Hertzian) Waves
« Reply #12 on: 18/07/2012 17:26:23 »
I was thinking the same thing about continuous waves being required, Hertz of course did experiments with a spark gap which I imagine (not being an expert or professional physicist myself) that it may not be possible to detect interference with a spark gap, but perhaps I'm wrong... anyway, I recently learned in viewing the PBS documentary film "Empire of the Air" that Marconi and De Forest both tried to cover an international yacht race in New York around 1903, or perhaps earlier, and interference was reported making both ineffective in their communication. For more you can read this rather amusing and humorous account from 1903 newbielink:http://earlyradiohistory.us/1903cuss.htm [nonactive]
...In any event, can this be considered the first recorded account of interference, or was it discovered and demonstrated in radio waves at an earlier time?
« Last Edit: 18/07/2012 19:10:32 by jjibex »
 

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Re: Destructive Interference in Radio (Hertzian) Waves
« Reply #12 on: 18/07/2012 17:26:23 »

 

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