A guide to receive far away FM stations

[essbebe]

@mcx for a simple circuit
Active FM-Amplifier

 

[mcx]

Hi essbebe, I have built that simple active fm circuit but I dont know why but it is not working ,i am not an electronics profesional but i have made many simple hobby circuits without any problem .I am presently using a tv vhf booster having a 3 transistor amplifying circuit with the same transisiter as that in that active fm circuit that old booster good for fm as well but may be optimised for tv signals , i'm presently using quad antenna (i was early using yagi antenna) with these things I'm able to catch almost all stations from kerala , kovai, nellai kodaikanal trichy some stations from karnataka and sri lanka all here in kottayam in kerala. But these distant stations are fluctuatiing wax and wane in power all the time especially in the daytime,i am trying to make these signals more stable, can anything be de done about it.Or is it out of our hands, simply left to weather conditions... anyway thanks for the reply

 

[essbebe]

@mcx Good show. Always make any Yagi or Quad Antenna to say 98 MHz the mid frequency of the Fm B/C band 88 to 108 Mhz.Height is important and rotating the antenna towards the Transmitter also helps. Of Course weather also plays a part but during , summer many distant FM stations can be picked up. See post 31 for a tuned circuit in aerial/antenna side.
Google "Kerala Amateur Radio club" and find some club in Kottayam.
Try this club.
P.O. Box 335, Kollam, Kerala 691 001
Phone: 0474-748771

 

[mcx]

Hi thank so much for the reply... Actually I made the antenna for 98 Mhz but after building it ,it went little shorter may be for 100 Mhz anyway I had better perfomance with 2 element quad than my old 6 element yagi; but searching through net i find most of them use yagi or very long quadrangular antenna for fm.Although I love to but I cannot possibly increase the height, furthur. I 've been turning this to different directions, these days too much of overlap and by simply changing the direction the station changes esp in freq like 93.5 many suryan and SA fms , three radio mirchi 98.3 ,club fms and radio one in 94.3,radio mango from kannur thrissur from the same direction. I'm presently thinking 0n adding directors to have a better directivity of the antenna in order to reduce the interference problems because even though I'm getting many stations overlap problem makes them un-listenable.. I really enjoy working on radios and really love to share the experience with other fm lovers... Really love to hear from u & thanks a lot for ur reply with regards mcx

 

[essbebe]

What is the cable you use to connect from the Quad Antenna to the Fm receiver?.for reception it is not very critical, I would suggest you use a 50ohms cable. I think it ..is RG58u. ( A thin cable. costlier is RG8U thicker but not needed for you ) This will ...match the impedence and you get better gain. The ribbon cable we use for TV is 300 ....ohms impedence type and won't match your quad.

 

[mcx]

What is the cable you use to connect from the Quad Antenna to the Fm receiver?
.for reception it is not very critical, I would suggest you use a 50ohms cable. I think it ..is RG58u. ( A thin cable. costlier is RG8U thicker but not needed for you ) This will ...match the impedence and you get better gain. The ribbon cable we use for TV is 300 ....ohms impedence type and won't match your quad.

Exactly !!! , i have posted this problem in this forum earlier but nobody replied, thank u so much. My quad is supposed to be 75 ohm impedance but my booster is 300 ohm & I dont have a 75 ohm booster or a circuit diagram .I am using 300 ohm ribbon about 1.5m from ant to booster, 75 ohm coax from booster to receiver, because this was the better combination I found out by trial and error,because when I put 75 coax from antennae to booster the result was so bad,replacing ribbon cable by 75 coax from booster to receiver had a marginal improvement.
there is indeed an impedance mismatch but trying balun at the ant side was disappointing I haven't tried 50 ohm cable still, is it available in the electronic stores in kerala ? if I could get that I would definitely try connecting the antenna to the receiver directly, bypassing the 300 ohm booster..... expecting replies

 

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[mcx]

@essbebe , if i use a RG58u cable what booster should I use

 

[essbebe]

The TV Antenna Booster ( mounted at aerial end) used a ribbon cable which goes to the Balun in T V stepping down the impedence from 300 Ohms to around 75 Ohms. You can try RG58u to Fm Rx direct. If it a self made Booster the amplified signal coming thru a capacitor to RG 58u cable can be connected directly to the FM Rx antenna point. Usually the Input impedence is around 75 ohms in all Receiver na Antenna input points.As i told earlier for reception of VHF signals this minor loss is barely noticed.

 

[mcx]

@essbebe thanks the rg58u cable is 50 ohm ?used for gen radio comm ? right? now there is no specific booster for it, is that so ?If i connect the cable dir to ant without booster whatever signals received at the antenna will that be carried without much loss at the other side ?,this was not happening with the 75 coaxial cable

 

[essbebe]

@mcxIn electronics never commit to any definite answer! (* conditions apply!)If the Input and Output impedance is matched maximum energy is transferred.( Thevenin's theorem)Yes . Should be some improvement.Also when you try a Yagi antenna the impedance is not always 50 ohms, and goes lower and lower with increase in no of elements !.Actually RG 8u ( thick cable and costly ) is better than RG58U. We also work out loss in signal strength ( attenuation) for the cable length used. The longer the cable more the loss!Finally trying different combinations, the final improvement in reception is what matters .IGNORE: beyond this thread subject. For reception , not critical, but for transmitting , we take extreme care not to damage the VHF transmitter's output stage. . ( Another test instrument SWR meter used and an Antenna tuner, either automatic or manual with coil, condenser tapped combinations).