TopBand: Re: Why the duct?

Wed, 9 Jul 1997 09:03:15 +0000

> From:          K3BU@aol.com
> Subject:       TopBand: Re: Why the duct?
> Date:          Wed, 9 Jul 97 02:02:25 +0000

> I believe that on the way of signal to and from our antennas (and
> ionosphere), it goes through the atmospheric layers (various compositions,
> temperatures, etc.) with varying dielectric constant, which would change the
> angle of refraction. 

What is the change in dielectric constant with temperature of air at 
1.8 MHz?

Does the two meter signal refract or duct because of temperature 
changes, or MOISTURE layers caused by the temperate gradient? 

Do moisture layers affect ten meters, twenty meters, 160m meters, or 
mainly UHF and microwave?

Is the temperature more important in dielectric constant, or the 
moisture content?

The answer is the temperature has almost no effect at all, while the 
moisture content has a much larger effect. The largest effect is at 
higher microwave and optical frequencies, decreasing greatly at VHF 
and all but gone at ten meters.  

>As we definitely know from VHF we can duct at quite low
> heights.

160 propagation is "more than slightly" different than propagation 
two meters. Equating the two is like munching on Exlax 
instead of a chocolate bar, the effects are totally different.

> be detected. Sure looks like that signal is "floating" up there, and it might
> be just atmospheric condition that will let it through to a particular spot
> on earth.

Dark travels at the inverse speed of light,that's why shadows 
disappear at the same speed light appears, and they don't collide. 
The signal might be floating at the speed of dark which is 1/C 
where C is the speed of light in centimeters. 

Perhaps the radio wave is caught in the twilight zone where it is 
alternately reversed by the speed of dark, and fast forwarded by the 
speed of light. Eventually, near the crack of dawn, it spills out.

I almost think we could bottle this radiation, and later uncork it 
and pour it in a glass to wash down our chocolate bars.

> In the mean time I am looking for any unusual (good) spots for contest
> station (like salt water lake on the top of the hill, overlooking ocean) on
> the coast from ME to DE, will travel to check it out with my radiomobile.
> Anyone with tips or experiences, please let me know. 

Why? If the propagation is from ducting, the ground beyond ground 
wave distance from the antenna will have no effect at all on the 
signal. 

>From your earlier postulations, I'd think you should be looking for 
a location where the temperature is conducive to two meter ducting, 
like near Lake Erie during summer mornings in spring or fall..

73, Tom W8JI 

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