Inversion

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Inversion

Postby m0lsx » Mon Jan 20, 2014 10:18 pm

I have just been driving to collect my daughter from Sea Scouts & it's foggy out there & for those who do not know fog can be winters propagation..
Temperature Inversion is similar to the effect seen when a stick is pit into water.The signal bends & travels further, or can..This is caused by fog making the temperature at earth level lower that the higher atmosphere..Inverting the normal situation..
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Re: Inversion

Postby Frequency Hopper » Tue Jan 21, 2014 1:33 am

Interesting as I did think that signals seemed to propagate good in fog at least on a local VHF and UHF level. I have a very basic understanding of how weather affects radio signals. I know how HF propagation works and how signals can bend and bounce and have a basic understanding of sunspots. In real life though I go by what results I get and have noitced fog conditions are good for local signals and maybe HF too although VHF and UHF is my primary monitoring area.

The rain on the other hand has the opposite effect and causes worse reception on local bands. I find the summer is much better than the winter. All the above is based on my own observations.
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Re: Inversion

Postby m0lsx » Tue Jan 21, 2014 8:49 am

Frequency Hopper wrote:The rain on the other hand has the opposite effect and causes worse reception on local bands. .


True, but those who work up in the GHZ area, find that sometimes rain produces what is called rain scatter, this is caused by the rain drops themselves "remiting" part of the energy that has hit them, this can produce some very good DX, by microwave standards...However having said the above, the signals worked by rain scatter are not good, so despite it producing DX, it is also often almost unreadable signals...
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Re: Inversion

Postby Mark5R » Tue Jan 21, 2014 12:34 pm

Yes I get it bad on the lower bands when it rains but it doesnt really affect vhf high and uhf. What is it that causes a "lift"? is that all down to sunspots, weather conditions or both?
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Re: Inversion

Postby milly » Tue Jan 21, 2014 2:27 pm

Mark5R wrote:Yes I get it bad on the lower bands when it rains but it doesnt really affect vhf high and uhf. What is it that causes a "lift"? is that all down to sunspots, weather conditions or both?


Temperature inversion is nothing to do with sunspots as such (excepting that they affect the weather).

Entirely down to weather conditions. Several things can cause a temperature inversion. Normally the temperature of the air above us decreases with altitude. An inversion is where there is an area of air some distance above us that is slightly warmer than the air both below and above it. At the right height this causes the radio wavelengths we are interested in to reflect back to the earth over a greater distance than would normally occur - effectively it increases our radio 'line of sight' beyond the normal radio horizon.

Several years ago the BBC Engineering Dept. (in association with the MET Office) published a document which explained the four main causes of temperature inversion - might be worth searching the BBC website in case they put it online. It was very detailed and technical but well written so easy for non-engineers/meteorologists to understand.

'Lift' is a rather general term for improved propogation and the causes/reasons are many and various - some affect HF, some higher freqs.
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Re: Inversion

Postby m0lsx » Tue Jan 21, 2014 2:34 pm

Rain & even green, but especially wet leaves will cause big attenuation issues on UHF. It is called path loss.
And propagation can be caused by a variety of things, some of it is ionospheric some is tropospheric...
As a basic, the Ionosphere is about 100 to 600km in altitude & the troposphere is the area below that..
What effects the different levels & how it effects radio waves is both diverse & complex.
Fog as mentioned earlier causes the earth level atmosphere to become colder than the higher troposphere & this can cause propagation, but air pressure differentials, can also cause an inversion at a higher level in the troposphere..
At the Ionospheric level things like sunshine, sun spots, solar winds & a few other factors can all have an effect. With the MF bands we can see seasonal & day night alterations brought about by sunlight & conditions like grey line, the area either side of dawn, dusk, can provide DX conditions as high as 30MHz.
If anyone is interested in finding out more then Ian Poole (G3YWX) has produced an excellent & basic book on propagation called Radio Propagation - Principles & Practice, which is available from the RSGB for only £9.99
http://www.rsgbshop.org/acatalog/Online ... on_45.html
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