[Elecraft] Critical frequency

Sat Nov 23 21:46:01 2002

There is a handy dandy 'aid' I really like called dxatlas. I like it because
it shows a map of the world with greylines, has prefix lookup, etc. All
sorts of worthwhile goodies to play with.

For those interested in propagation the latest version also overlays
ionospheric data (MUF, F2 layer critical frequency, F2 layer height,  E
layer critical frequency, D layer peak density. Auroral activity). and
geomagnetic data (Geomagnetic latitude; Corrected geomagnetic latitude;
Magnetic dip; Modified magnetic dip; Magnetic dip latitude.) data. It's all
updated based on your PC clock time & date.

www.dxatlas.com

They also just released IonoProbe. its function is to "Monitor space weather
indices and helps you learn what those indices mean" and   "IonoProbe
downloads near-real time satellite and ground station data, stores
information for future use and displays it in a user-friendly way."

www.dxatlas.com/IonoProbe/

I have no connection with tha author other than admiring his work. Enjoy

Mike K5PU

----- Original Message -----
From: "Kevin Rock" <[email protected]>
To: <[email protected]>
Cc: <[email protected]>
Sent: Saturday, November 23, 2002 6:37 PM
Subject: [Elecraft] Critical frequency

> Being a curious sort I looked up critical frequency.  This is what I
found:
>
> Near-Real-Time F2-Layer Critical Frequency Map
>
> The following image is a recent high-resolution global map of F2-layer
critical frequencies. This corresponds to the maximum radio frequency
> that can be reflected by the F2-region of the ionosphere at vertical
incidence (that is, when the signal is transmitted straight up into the
> ionosphere). It is also a map showing the current location of the auroral
ovals, the sunrise/sunset terminator and the regions of the world
> where the sun is 12 degrees below the horizon (which estimates the
gray-line corridor where HF propagation is usually enhanced). This is
> one of a plethora of constructable maps that is produced by PROPLAB- PRO
Version 2.0 (formerly known as SKYCOM PRO), a very
> powerful radio propagation software package for IBM or compatible
computers, ideal for amateur or professional radio communicators.
> Instructions on how to use this map follow below.
>
> This was found on : http://www.spacew.com/www/fof2.html
>
>    73,
>         Kevin.   KD5ONS
>
>
>
> 11/23/2002 5:25:35 PM, "Ron D'Eau Claire" <[email protected]> wrote:
>
> >"Critical frequency" is defined as the lowest frequency at which a
> >signal beamed straight up will still be refracted straight down by the
> >ionosphere.  Signals beamed straight up which are at a
> >higher-than-crticial-frequency will penetrate the ionosphere.
> >
> >The critical frequency varies with time of day and solar activity, of
> >course.
> >
> >73, de Earl, K6SE
> >
> >That's a new one on me, Earl, since "refraction" is bending, not
> >reflection. The less refraction, the further away the signal returns to
> >earth. At some point between the amount of refraction that occurs and
> >the angle at which the signal interacts with the ionosphere the
> >refraction still bends the signal, but not enough for a return to the
> >surface. That is what I have always understood is the "critical
> >frequency". Signals at higher angles (including 90 degrees or 'straight
> >up') will pass on through as well.
> >
> >Ron AC7AC
> >
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>
>
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