A guide to receive far away FM stations

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mundle2002

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Hi everybody,
After reading the previous posts, i thought to share something which might be unknown to some people. Receiving far away FM stations is called FM Dxing. I am from Ranchi(Jharkhand) and unfortunately here we dont have private FM stations except Vivid Bharti:wall: . But i do listen to FM stations of Kolkata(Calcutta).
I want to make it clear to everybody that high frequency signals travel in the line of sight and these high frequency signals can either be FM or AM.
So, saying that FM signals travel in the line of sight is partially correct.
Low frequency signals like MW and SW also travel in the line of sight but they also get reflected by the one of the layers of atmosphere. So we can listen to faraway stations in these bands.
High frequency signals do not get reflected rather they pierce the layers of atmosphere and are lost in space leaving only one option: line of sight transmission.
But there is a special layer in the atmosphere called ionosphere which helps in reflecting the high frequency signals. Although not always present, this layer is responsible for FM Dxing.
To receive distant signals you need:
1) A good FM receiver. (I have got my Sony home theatre which works very well)
2) An FM Booster(Not those TV boosters):confused:
3) A home made antenna.
You can get a plenty of circuits diagrams in the internet for FM booster.
Print out the diagram and either make it yourself or give it to the technicians who repair TV and radio.
The antenna can be a simple one like a whip antenna if you want to listen to nearer stations or it can be a complicated one like Yagi antenna. I made a quadrangular antenna.
With the help of above things, i receive FM stations of Calcutta. In a straight line it is more than 350 Kms from Ranchi. The signals become clearer in the night and they become stereo from mono.
Thus my setup receives whatever signals it gets from line of sight and from ionosphere reflections.
Some other facts:-
Aircraft communications also use high frequencies (118-136Mhz) and they talk in line of sight BUT THEY ARE NOT FM, they are AM (amplitude modulated) signals like those of Medium wave and Short wave.
One interesting thing:- One day when i switched on my system i wasnt able to receive Kolkata FM stations rather i was receiving radio stations of Burma(Myanmar) . I took out the map and measured the distance of Burma. It was more than 1500 Kms. Isnt that interesting:yahoo:May be due to changes in the ionosphere i was able to receive them.
It might seem surprising to you that i am a Doctor but electronics and communication is my hobby. I hope you enjoyed reading my little article. Need any help?
 
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cyberwiz

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I once managed to receive radio stations from middle east..ie dubai & saudi Arabia..it was a long time back on my Pioneer deck but this was without using any special antenna..and yes Signal was better in the night..presumably due to refraction..?
 
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boygr8

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great work mundle2002, I am a Doctor too, & my hobbies are very similar to urs :)
 
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coolbuddy_79

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my TV catches the ATC talks so many times :p
 
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Very good information, thanks.:thumb:So is that same reason by which I receive Mumbai FM in Pune which is 160-170 KM away?And I too have same observation, at evening the sound clearity increases & channnels are heard in stereo (STEREO indicator on Sony music system turns ON)
 
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delhilama

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Good information mundle. I would like to add that, FM signals do reflect and can be received in far flung areas (without signals being available in a large continuous area).I have another recommendation for people in far areas. Use an omnidirectional external antenna (such as rabbit ear, Loop antenna, or even a dipole). Directional antennas such as Yagi are only suitable in cases where there are only one or two channels of broadcast available and they are almost in the same direction from point of reception.Oh yes, the quality of cable that connect the antenna dipole and booster and then the receiver, must be of good quality (75 ohms with immeasurable loss under 30 feet).
 


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srinirao

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Nice guide for FM enthusiasts...Sometimes back while googling i came across a shoutcast IP Live radio channel link where i was able to stream the Delhi RadioCity contents through WinAmp Media Player.I think this will be the most easists way to receive Internet radio channels over IP. google to find more details on this.
 
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mundle2002

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Regarding antennas, A dipole is a bidirectional antenna not omnidirectional.A whip antenna used in portable radios is omnidirectional. When one or more directors and a reflector is added to a dipole, it becomes unidirectional and is called a Yagi antenna. Its gain increases by the number of directors you add. Usually antenna length i.e. length of the dipole is calculated by taking the centre frequency of of the FM band.For 88 - 108 Mhz, it is 98 Mhz. You can calculate the antenna length if you desire to listen to a particular frequency.
 
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raja_meghana

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Thank you for your valuable information. Relatively I am new comer to this forum. Can you please give external anttena details (lenghths of dipole, directors, and reflector with a minimum of 6 elements for stations 150-200 km away with an estimated transmitter capacity of 10-20 kw)? By the way, I would like to get a simple design for fm booster.

[email protected]
 
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mundle2002

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For the FM band with the centre frequency of 98 MHz, we have to first calculate the wavelength by the formula:-wavelength(in meter) = speed of light(m/s) divided by frequency (in Hz).therefore, wavelength = 300000000 m/s divided by 98000000 Hz. = 3.06 meters.The length of the antenna should be some multiple of the wavelength. This is because the antenna must present itself as a resonant circuit to the RF signal so as to maximize the power in the antenna.It can be either 1/4th wavelength = 75cm as those used in Radios.It can be 1/2 wavelength = 1.5m (a dipole)or a full wavelength.You can download the pdf of the article "Mosfet based amplifier for FM radio DXing" from the website of "Electronics for you" magazine.Although i used the antenna design from the article, i didnt use the circuit.I used the circuit from the article "FM booster". You can also get the same circuit from the website You can also design a Yagi antenna:-Length of dipole = 1.5m.Length of reflector = approx. 5% larger than dipole.Space between dipole and reflector = 0.2*wavelength.Length of 1st director = approx. 4% smaller than dipole.Space between dipole and 1st director = 0.12*wavelength.Make the 2nd director by decreasing 4% length as compared to 1st director,make 3rd director by decreasing 4% length of 2nd director............and so on.................you can add as many directors as you like.The inter-director spacing will be 0.12*wavelength.Although the Yagi antenna is a little bit bulkier and prone to breakage by the birds sitting on it, it will definitely give a greater gain compared to any other antenna.
 
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jishnu1980

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hello iam also new to this forumiam from kerala 4 private fm stations near to us (around 25 kms road distance(not air distance if it calculated only 15 or 16 through air) all the 4 players said that their signels cover 50 kms from the point of transmission but we dont get it clear inside our home using Sony home radio (in some rooms not even signals) but its clear in car audio using full length antenna this problem facing allmost all the peoples near to me any suggestion to get the signals inside the room clearly
 
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ItsMe

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@jishnu1980, This is a problem when you live in an area where there are lot of trees and other obstructions. You should be able to receive all channels clearly if you try tuning outside your house. The easiest and the cheapest solution is to go for an external antenna and a small FM booster. try checking with your local electronics shop.
 
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rishabh sethi

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fm where i will get a fm booster aand what will be its cost and a signal booster or fm booster which one