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A typical example of microwave signals being absorbed by a object in it's way,would be a microwave oven with a plate of food inside.this is why there are currently ongoing studies regarding the effects of a mobile phone and it's effects on the human brain,etc,etc.
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Posted: 2004-10-07 17:20:23
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Some nice info here by nut one must know, btw whiz if u want more of this info visit here http://www.howstuffworks.com :-)
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Posted: 2004-10-07 17:25:29
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Like aled quite rightly said,the higher the frequency,the lower the wavelength.for example,a cb antenna averaged 18ft long because it was on 27mhz(low frequency),whereas a mobile stub antenna is only 0.5in or near in length,because it operates on microwave frequency(uhf,shf).all very interesting stuff to some.
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Posted: 2004-10-07 17:26:44
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I see (I think!) I also have a short-wave radio reciever, and as the short wave frequencies I believe are very low - you can pick up signals from the other side of the world (as I have done - with a normal radio antenna the SW radio came with!). And therefore as I understand it this is why radio hams have huge antennae in their back gardens?
btw I've had a look in the howstuffworks site, and picked a few things up and a general outline, I'm also interested in a bit more detail on how phones and the transmitters operate.
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Posted: 2004-10-07 17:37:34
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Quote:
On 2004-10-07 01:02:23, harvey172 wrote:
Ur the whizkid u shud no!
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Posted: 2004-10-07 18:25:47
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I could explain how transmitters and receivers work,but it would take many posts.yeah radio hams use 144-146mhz(2m band),and i think 430 to 434mhz(uhf 70cm band).many people are under the impression that a large antenna works better,whether it be for receiving or txing,but it's quite simply not the case.like i said a cb transceiver works on 27mhz(hf) and uses a huge vertical 18ft(or horizontal)antenna.if you was to use this antenna on a phone,the mismatch would be huge,and the phone would barely function!
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Posted: 2004-10-07 19:41:14
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It's all done with invisible lengths of string.
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Posted: 2004-10-07 19:50:15
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Here are some basic radio facts;radio waves(rf)travels at 300,000,000 m/s.a simple way of working out antenna length is like this;i'll use a phone on 900meg as an example(o2,voda)300000000(speed of rf)\\900000000=0.333,which means gsm 900 would be on the 30cm band.antennas are often half wave,or quarter wave.so the full aerial length would be approx 7cm(remember the coils inside old stub antenna)in full length when uncoiled.
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Posted: 2004-10-07 19:55:01
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