A guide to receive far away FM stations

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mcx

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thanks essbebe , will 90 degree turning work with quad antenna to receive vertical polarisation ?, i think our transmitters are definitely vertical and may be both vert and horizontal, is it not ? anyway i will try tomorrow morning. now the reception is generally bad since so much of heavyrain and lightening towards the evening in kerala: makes the distant Fms noisy.May be due to effects of global warming we are getting record summer rainfall. and HAPPY VISHU to all of u in this forum bye
 
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mhtplsh

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Does anybody have ampifier circuits designed specially for fm band rather than vhf tv booster ?

Yes! i hv decided to develop the same. 88~108 mhz with precision bandpass filter. So no interference from tv channels.
It will be a 2 stage with min. 25db gain & return loss of more than -18db.
 
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essbebe

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see the circuit given there. Whether copied from Popular Electronics, or an American web site or EFY makes no difference. Theory is same. But nowadays very difficult to get electronic parts for home construction.

https://broadbandforum.co/fm-radio-stations/24979-fm-radio-reception/

Your FM radio tuned circuit is for 88 to 108 MHz.
The bandwidth allowed in the IF usually 10.7 Mhz with a narrow B/W
for B/C audio.
So no possibility of local TV station breaking through. even if you use a untuned RF amplifier.
assume your TV audio FM signal say 67.75 round it to 67.7
When you tune 88 MHz the L.O will be 88+10.7= 98.7 MHz
When you tune 108 MHz the L.O will be 108+10.7 = 118.7 MHz.
So TV FM audio cannot generate the 10.7 MHz IF.
98.7 minus 67.7( approx) IF 31 MHz
118.7 minus 67.7( approx ) IF 51MHz.
You can check this. A local FM say 108MHz will be heard around 88MHz also.
108+10.7=LO 118.7 Normal 88+10.7=98.7 LO (image)
signal 108 mixes with 98.7 to give reception when dial shows 88 MHz
 
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mhtplsh

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see the circuit given there. Whether copied from Popular Electronics, or an American web site or EFY makes no difference. Theory is same. But nowadays very difficult to get electronic parts for home construction.

https://broadbandforum.co/fm-radio-stations/24979-fm-radio-reception/

Your FM radio tuned circuit is for 88 to 108 MHz.
The bandwidth allowed in the IF usually 10.7 Mhz with a narrow B/W
for B/C audio.
So no possibility of local TV station breaking through. even if you use a untuned RF amplifier.
assume your TV audio FM signal say 67.75 round it to 67.7
When you tune 88 MHz the L.O will be 88+10.7= 98.7 MHz
When you tune 108 MHz the L.O will be 108+10.7 = 118.7 MHz.
So TV FM audio cannot generate the 10.7 MHz IF.
98.7 minus 67.7( approx) IF 31 MHz
118.7 minus 67.7( approx ) IF 51MHz.
You can check this. A local FM say 108MHz will be heard around 88MHz also.
108+10.7=LO 118.7 Normal 88+10.7=98.7 LO (image)
signal 108 mixes with 98.7 to give reception when dial shows 88 MHz

i think u r not much familiar with cable tv technology.
More the different signals at the booster input, more the mixing of different frequencies. Check the filters of adjacent channel tv modulators & their mixers. If the filter is not attenuating -60db of adjust channel audio & video, it is getting over. This is not the place to go more in detail.
I hv done the market survey also. I got the info that at many places they get tv sound in the fm channel. They are using vhf boosters. Hence we hv decided to go our own way. Developing proper fm booster.
 
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subbu68

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a bit about me. Hail from Ernakulam but working in Abu Dhabi. An electrical engineer from REC Nagpur dealing with EHV substations but having interest in electronics from childhood. Revived the interest about 3-4 years ago when my Bose system did not receive FM stations here. Memeber of AV Forums and Yahoo Groups on Sangean ATS 909, Sony 7600GR. Came across this forum while searching for FM Stations in India when I went on vacation in August 2008. On reading through this thread I think there is some misconception regarding antennas and the connections. Open ended Dipoles have a charateristic impedance of 75 ohms. So a 75 Ohm cable is the best match. normally all receivers are designed with 75 ohms input imepdance for FM (or some with an inbuilt balun for 300Ohm lead in cable). Hence, RG6 or RG59 cable should be used for FM reception. Nevertheless, you must use a 1:1 balun to match the unbalanced coaxial cable to balanced antenna. A simple balun is just 5 turns of the coax about 1 inch diameter at about 2 inches from the connection point to the antenna . Atleast for 1/4 wavelength the cable should be at 90degrees to the antenna to avoid stray pickups. Dipoles are directional if mounted horizontal and omni when vertical. Yagi are made of dipole with reflectors and directors to make it narrow band. 50 Ohms is normal for transmitters / tranceivers. Ground plane atennae are 50 Ohms.There you use RG8 or RG58 cables. A J pole is another Omni solution. It worked for me but the municipality do not allow ugly antenna sticking out of the apartments. So removed it. Folded dipole have 300 Ohms impedance and there you use a 300 ohm ribbon cable or use a coax with proper balun. I am using vertical omni dipole with RG6U cable and 1:1 balun to catch FM stations 160kms from Abu Dhabi in Stereo mode. This is the most 'invisible' solution I can think of for my setup. Of course weather plays an important part in reception. For omni directional antenna you could have two dipoles at right angles and connected with a 1/4wave delay line. But you may have to live with multi path interference. Present FM stations have both horizontal polarisation and vertical. H polarised were used in the olden days when people used to listen to radio sitting at home with old bulky radios. When radios became small and were available in cars you couldn't have H polarised for proper reception. You need V polarised fo proper car / mobile reception. So all stations have both H and V. In FM you have to also fight with multi path distortions especially in urban areas and for that you need an antenna with very narrow band.. A Yagi. You need a rotator for serious DXing to narrow on the desired station Similarily if you have tuner with a wide band filter you may hear muddled sound due to interference from adjascent stations. A good tuner with a narrow band filter and Yagi with rotator would make a lot of difference There is no common solution for proper FM listening unlike SW. Correct me if wrong. SubbuBose 321 HTS, SONY BRAVIA KLV-40D300A,Yamaha AX496 Amp, Yamaha CDC 685 CD Changer, Yamaha KXW421 tape deck,Jamo E855 spkrs, SANGEAN WR3, SANGEAN ATS 909, SONY 7600GR PC SELF MADE - E6750/2.66GHz,2GB RAM,580GB HDD
 
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shantam2005

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Hey using this method can I recieve stations from 170-270km away?
 


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mcx

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hi, it is always possible to get fm stations from 100-200 km distance. how good the reception will depend on the altitude of your location and weather : if u r living in a plain area with no hilly areas coming in near sight, it is good.If you are in a hilly area sorrounded by still higher mountains then u may not receive the signal at all ,if in a city and living at 15 th floor apartment then reception of the distant stations will be very good ,if your location exceptionally high altitude > 1000 meters from sea level with good horizon view all around then stereo reception will be possible for even very distant stations (450 km or more away) with inexpensive radio sets. Obviosly a good antenae ,amplifier will enhance the reception.
 
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Sushubh

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i have noticed that FM quality gets worse after moving 100 KM from delhi. till that area it's pretty good.the problem areas are where you are somewhere in the middle of two major cities. the radio tries to catch stations from both the cities and u end up with a mess. i have noticed the problems while driving to agra. for a distance of around 10 KM, the radio is simply useless as the stations are noisy and u end up hearing two songs interfering with each other.
 
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nav9306

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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?


hello everyone
i am from cochin
a student interested in receiving far off FM stations
though i have many nearby stations , out of hobby and curiosity i would like to listen to far off stations
someone pls help me to do the necessary
should i buy the FM booster kit or the mosfet based preamplifier available in electronisforu.com ???
also about the type of antenna that i wud need ( i live in a city with lot of buildings near my house )
any help wud be appreciated