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Re: [RTTY] About N4II's experiment...

To: Kok Chen <chen@mac.com>
Subject: Re: [RTTY] About N4II's experiment...
From: Kai <k.siwiak@ieee.org>
Reply-to: k.siwiak@ieee.org
Date: Sat, 15 Mar 2014 07:30:26 -0400
List-post: <rtty@contesting.com">mailto:rtty@contesting.com>
You're quite right Chen. At the risk of annoy the moderator with off-topic discussions, time-of-flight is not all that needs to be measured, but it is necessary to a certain precision. The probe signal is quite a bit more sophisticated. The signal bends in three dimensions, separates into counter rotating waves of circular polarization that travel different paths and at different propagation velocities, possibly reflects and diffracts from the gray line region and Auroral oval boundaries. It is subjected to multipath and ISI, and so on. It's a digital signal designer's heaven (and a propagation weenie's heaven)! Competing theories predict different paths, as well as different multipath, and differing propagation velocities. The ionosphere is complex, and then you add the Earth magnetic field, and things get really interesting in a hurry (think CRT). It's not like simple AFSK, where you just need to follow the manufacturer's instructions.

73,
Kai, KE4PT



On 3/15/2014 12:23 AM, Kok Chen wrote:
On Mar 14, 2014, at 8:49 PM, Kai wrote:

We do however want to measure the propagation speed of signals in the 
ionosphere...
There are more unknowns than measurables, Kai, if all you are measuring is the path 
transit time.  The problem is not the "baud rate" (we know for example that it 
is easy to measure transit time to much more precise than T, using a pulse whose width is 
T).

Think of a similar experiment where you use total internal reflection of a 
prism in a reflex light path to measure the speed of a laser beam.  You don't 
know the size of the prism, nor the distance of the laser to the prism, and you 
don't know the refractive index of the glass used to construct the prism.  All 
you can do is to measure the transit time as precisely as possible.  With that 
alone, you cannot determine the refractive index of the prism.

Now imagine the prism to be a simple model of the ionosphere.  (In the case of 
the ionosphere, the density is not even constant.)

73
Chen, W7AY


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