The amount of difference in signal high pressure makes

Steve_W

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Just out of interest, down here in South East Kent, currently the atmospheric pressure is 1024 mb. Normal is around 950 (I'm led to believe, I'm not a pro!).

So when I connect my spectrum analyser to an incoming aerial to see what the signal is like, I'm seeing an increase of around 8db.

Is there any type of scale that exists to work out how much the signal raises or lowers according to pressure by frequency in mhz or UHF channel allocation? Lots of my customers are getting co-channel interference due to flooding from Belgium & France in certain coastal areas, it would help me if I knew.

I usually look at the propagation charts here for this info:

http://www.dxinfocentre.com/tropo_eur.html#hour6

And this for my local one:

http://www.worldweatheronline.com/Margate-weather/Kent/GB.aspx

Thanks guys!
 

Huevos

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Mean atmospheric pressure is 1013mb. Typical low would be down to about 980mb, and 950mb somewhere in a tropical cyclone (i.e. an event). None of this is directly related to your 8dB gain though. What you are seeing is increased tropospheric propagation, most likely caused by temperature inversion, i.e. normally air at ground level is warmer than the air above, but sometimes the air below is cooler. This can happen on very hot days due to the bottom few meters of troposphere being in contact with cool sea water while a few meters above the atmosphere is quite a bit warmer. This type of refraction affects a wide range of frequencies, all the way from VHF up to visible light and allows over the horizon viewing. Depending how pronounced the refraction is it can sometimes raise the French coastline above the horizon so it is easily viewable from the UK.
 

Hixxy1

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thecaretaker said:
Is this the same as what CBers and radio hams used to call skip?
Yes it's very similar. It's a different type of skip though as different frequencies behave differently.

Plenty of atmospheric skips today, with radio stations coming in from Europe.
forums.digitalspy.co.uk/showthread.php?t=1670783&page=86
 

PaulR

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More or less - yes. The high pressure causes the signals to travel further without attenuation.

There's also another phenomenom around at this time of year called Sporadic E although it doesn't really affect UHF frequencies. It's mostly notoceable on VHF and the top end of HF transmissions. Many years ago I was driving down through Shropshire listening to FM radio. This was before NF (Network Follow) and I had to keep scanning for a different transmitter. Suddenly a Spanish radio station (or maybe Italian - my language skills are none too good) came booming in. I was able to listen to it for about twenty minutes as I drove south until it just as suddenly faded away.
 

Channel Hopper

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PaulR said:
Many years ago I was driving down through Shropshire listening to FM radio. This was before NF (Network Follow) and I had to keep scanning for a different transmitter. Suddenly a Spanish radio station (or maybe Italian - my language skills are none too good) came booming in. I was able to listen to it for about twenty minutes as I drove south until it just as suddenly faded away.
Could be aliens then

http://www.youtube.com/watch?v=GOc01_Ty1eQ
 

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thecaretaker said:
Is this the same as what CBers and radio hams used to call skip?
No. Skip is caused by the ionosphere (high in the atmosphere), and enhanced by the sunspot cycle. It occurs between mainly between 2MHz and 30MHz (known as HF). Tropospheric propagation on the other hand occurs at low level and affects frequencies from VHF through to visible light.
 

Piltdownpaul

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We called it skip whether it was sporadic e or f2 layer ionization. Either way it wasnt groundwave so there would be one bounce at least!
 
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