[HCARC] Total Electron Count (TEC) of The Ionosphere

Kerry Sandstrom kerryk5ks at hughes.net
Fri Aug 26 20:55:13 EDT 2016


Gary,

Yes, very interesting.  The TEC delays electromagnetic waves depending 
on frequency.  The ionosphere made up of charged particles is a plasma 
and this frequency dispersion is characteristic of a plasma.  One of the 
big differences between civil GPS and Military GPS was the military used 
2 frequencies which allowed the calculation of TEC and then the removal 
of the excess delay due to TEC from the position measurements.  It looks 
like this data is based on the GPS measurements.

Another effect of the TEC is its distribution - its not a constant value 
from ground to space.  It has small irregular volumes of higher electron 
density.  Certain areas of the ionosphere have a lot of small volumes 
which disrupt the signal.  Instead of a clean signal the patches break 
up the wave front and different parts of the wave arrive at the receiver 
at different times.  This is a bad multipath problem and limits the 
total bandwidth that can be used. It also causes some slow deep fading, 
sometimes several seconds between peaks.  High rate digital signals, 1 
Mb/s and up require extensive error correction coding and large amounts 
of memory to continue operating.  On 6 meter TE scatter paths we see 
this multipath problem.  Often it is difficult to use SSB because the 
bandwidth of the propagation path is so low only CW is really useful.

Kerry

On 8/26/2016 10:38 AM, Gary Johnson wrote:
> NOAA released an interesting bulletin regarding a new site for watching Total Electron Content (TEC) of the ionosphere. TEC is the total number of electrons present along a path between a radio transmitter and a receiver. The Space Weather Prediction Center (SWPC) has deployed an updated and expanded version of its US Total Electron Content (US-TEC) model.
>
> Interesting.
>
> Gary J
> N5BAA
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