Quirky Atmospherics
Discussion
I just happened to use the seek thingy on my car stereo this afternoon instead of the usual preset button expecting to go to my local station for the news Radio4 NL came out. Pressing seek few more times revelled that the FM band Was chocker block with Johnny Foreigners.
Is this just quirky atmospherics or some sinister new EU plot to take over our air waves.
:shout:Back off Brussels.
Is this just quirky atmospherics or some sinister new EU plot to take over our air waves.
:shout:Back off Brussels.
HERE'S THE SCIENCE BIT (NO NOT THE BIG BROTHER CHARACTUER):
When charged gas molecules are produced by the energy of the sun (the ionosphere), the degree of ionisation varies with the intensity of the solar radiation. Various cycles affect the amount of solar radiation with the obvious ones being the daily and yearly cycles. This means that ionisation will be greatest around noon in the summer and at minimum just before dawn in the winter.
The output from the sun varies over a longer period of approximately 11 years. During the maximum of the solar sunspot cycle, there is greater solar activity and hence greater ionisation of the ionosphere.
Greater solar activity generally results in better conditions for radio/television propagation (increasing ionisation). However, very intense activity in the form of geomagnetic storms triggered by a solar flare can completely disrupt the layer of the ionosphere and block communications. This can happen in minutes and communications can take hours to recover.
Other atmospheric effects can affect radio propagation and may often extend the transmission of VHF and higher signals beyond the line-of-sight. The lowest region in the atmosphere, the troposphere, can scatter VHF signals more than 600 km - tropospheric scatter. Ducting is a phenomenon where radio waves get trapped by a variation in the atmospheric density. The waves can then travel along by refraction. Ducting usually occurs over water or other homogenous surfaces. This is more common at higher frequencies and has permitted UHF communication over distances greater than 2500 km.
Another phenomenon, sporadic E skip, is a seasonal occurrence, usually during the summer. A small region of the E layer becomes more highly charged than usual, permitting the reflection of signals as high in frequency as 200 MHz. This highly-charged region soon dissipates. Sporadic E propagation will occur for only a few minutes to a few hours.
Hence the extra stations ex[perienced in summer.
It's a bit different with AM, but similar principals apply. (more crap weaving in and out at night where stations broadcasts on the other side of the world (where it's still light) get beamed in.
So you're right about the atmosphere.
When charged gas molecules are produced by the energy of the sun (the ionosphere), the degree of ionisation varies with the intensity of the solar radiation. Various cycles affect the amount of solar radiation with the obvious ones being the daily and yearly cycles. This means that ionisation will be greatest around noon in the summer and at minimum just before dawn in the winter.
The output from the sun varies over a longer period of approximately 11 years. During the maximum of the solar sunspot cycle, there is greater solar activity and hence greater ionisation of the ionosphere.
Greater solar activity generally results in better conditions for radio/television propagation (increasing ionisation). However, very intense activity in the form of geomagnetic storms triggered by a solar flare can completely disrupt the layer of the ionosphere and block communications. This can happen in minutes and communications can take hours to recover.
Other atmospheric effects can affect radio propagation and may often extend the transmission of VHF and higher signals beyond the line-of-sight. The lowest region in the atmosphere, the troposphere, can scatter VHF signals more than 600 km - tropospheric scatter. Ducting is a phenomenon where radio waves get trapped by a variation in the atmospheric density. The waves can then travel along by refraction. Ducting usually occurs over water or other homogenous surfaces. This is more common at higher frequencies and has permitted UHF communication over distances greater than 2500 km.
Another phenomenon, sporadic E skip, is a seasonal occurrence, usually during the summer. A small region of the E layer becomes more highly charged than usual, permitting the reflection of signals as high in frequency as 200 MHz. This highly-charged region soon dissipates. Sporadic E propagation will occur for only a few minutes to a few hours.
Hence the extra stations ex[perienced in summer.
It's a bit different with AM, but similar principals apply. (more crap weaving in and out at night where stations broadcasts on the other side of the world (where it's still light) get beamed in.
So you're right about the atmosphere.
Scruffy said:Nah, according to Greenpeas and Fiends of the Earth, it's due to pollution from cars repelling our own radio waves while attracting transmissions from polluted cities abroad, spokesmen didn't say today - but if they had it would have made more sense than usual
So you're right about the atmosphere.
Living in near the water in South Devon, we get some unusual stuff happening.
I used to work in a TV repair shop. The antenna system we had was very highly amplified just to get a signal from our local (at the time) transmitter. In my years there, I saw french, dutch, german, Polish, and even a few russian stations !!. We regularly get interference from Froggy TV/radio. Some of the spanish FM stations aren't bad either. Trouble is, none of this lasts for more than a few minutes. It has been known in the past for french municipal radio gear to trigger all the local police repeaters. It is a major pain in the arse for them apparently.
Phil
I used to work in a TV repair shop. The antenna system we had was very highly amplified just to get a signal from our local (at the time) transmitter. In my years there, I saw french, dutch, german, Polish, and even a few russian stations !!. We regularly get interference from Froggy TV/radio. Some of the spanish FM stations aren't bad either. Trouble is, none of this lasts for more than a few minutes. It has been known in the past for french municipal radio gear to trigger all the local police repeaters. It is a major pain in the arse for them apparently.
Phil
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