FM transmitter antenna - Electronic Circuits Projects Diagrams Free

juan123 · 9th August 2006, 03:31 AM

Well, I posted about modifying a tunecast FM transmitter. I added an antenna and the range has improved dramatically. Well my query is , how could I build an antenna that would not use too much space, but at the same time give me much more range than what I have now? My current antenna is just a 15ft long wire going up to the 3rd story of my house, from the 2nd story. I'd like to build an antenna that would boost my signal much more than that wire. I'm thinking maybe an electronic antenna that is powered?(If those exist.) I'm kind of a newbie with electronics, but I do know basics-intermediate level of electronics. Thanks for any help!
BTW the FM transmitter is working at 88.1-88.7 mhz, if that helps at all to help you experts with the numbers. Thanks!!!!!!!

mister_e · 9th August 2006, 04:12 AM

I don't know in your country but i believe it's illegal to broadcast within this frequency range for long distance. FM modulator and cheap wireless microphone use it... but for few inches, feet.

stevez · 9th August 2006, 11:17 AM

Juan - I'd encourage you to work within the limits of the laws. With that said I'll offer some information in the form of comments or statements.

A. Some antennas radiate in all directions - some in specific directions. Directional antennas can provide a stronger signal in one direction (at the expense of other directions) with the same level of power. A beam or yagi beam can do that.

B. A transmitter connects to an antenna directly or via a cable/wire called a transmission line. The transmitter output will be maximum when the transmitter is matched to the load - which is the antenna/transmission line.

C. If the transmitter connects to the antenna via a cable/wire - a transmission line - one needs to consider that all of the power won't get to the antenna - some will be lost in the transmission line. The lowest losses occur when antenna and transmission lines match and the transmitter and transmission lines match.

D. An amplifier could be used to increase the power output of the transmitter.

E. Transmitters put out signals on the frequency of interest and other frequencies. Simpler transmitters are likely to be worse in this sense. A better antenna will radiate the stuff you want better - and maybe the stuff you don't want to radiate. The same is true for an amplifier - and it can generate it's own extra RF signals.

I am sure this barely scratches the surface for you however it's not a simple subject.

HiTech · 9th August 2006, 12:49 PM

connect it to one leg of the AC wiring in your apartment, that way you'll use a majority of the wiring as an antenna. That'll do ya!

RadioRon · 9th August 2006, 04:48 PM

Quote:

Originally Posted by juan123

Well, I posted about modifying a tunecast FM transmitter. I added an antenna and the range has improved dramatically. Well my query is , how could I build an antenna that would not use too much space, but at the same time give me much more range than what I have now? My current antenna is just a 15ft long wire going up to the 3rd story of my house, from the 2nd story. I'd like to build an antenna that would boost my signal much more than that wire. I'm thinking maybe an electronic antenna that is powered?(If those exist.) I'm kind of a newbie with electronics, but I do know basics-intermediate level of electronics. Thanks for any help!
BTW the FM transmitter is working at 88.1-88.7 mhz, if that helps at all to help you experts with the numbers. Thanks!!!!!!!

I am glad to hear that you have succeeded in improving the range. What you are using right now is a random long wire antenna, one that is not specially tuned for your frequency, but rather just made as long and as high as you can. This is a good first step. The next step may be to try and tune what you have or replace it with a slightly different version that is better tuned. The trouble is that I am not confident that you can measure or sense small improvements in your antenna. How will you be able to tell if it improves by, say, only 20% more range?

A resonant antenna, such as a dipole might work a bit better, but you would have to make the antenna and then place it up high and then run a transmission line. Do you have any coax or twinlead transmission line?

It is possible to make a directive antenna for more signal, but you would need to master the basic resonant half wave dipole first.

chiba · 10th August 2006, 04:06 AM

How about this then?

stevez · 10th August 2006, 11:14 AM

Chiba's attachment shows a dipole. If kept clear of other conductive objects it will have a feedpoint impedance that will be an approximate match for 50 or 75 ohm cable. A common output impedance for transmitters is 50 ohms so this ought to be a good match. If all you have is 300 TV twinlead you can make that work with baluns (transformers) or you can just make sure you use integral odd multiples of half wavelength twinlead. Note that the wavelength must be the electrical wavelength for the cable - not in free space -or about 92% of the free space wavelength. This will essentially repeat the feedpoint impedance at the transmitter and provide a good match if it's 50 to 75 ohms.

For line of sight communications polarization matters. If you orient the transmitter antenna horizontally then best reception will occur if the receiving antenna is horizontal and the same holds for vertical - transmitting antenna and receiving antenna should be vertical. A dipole can be mounted either way.

juan123 · 10th August 2006, 01:31 PM

Thanks, I will try all of your suggestions.....Recently I've been having some trouble bc a radio station operates at 88.1 , which is the frequency I use and there's other radio stations at 88.5, 88.9. My transmitter only works with : 88.1, 88.3, 88.5, 88.7...which would mean that I will have a lot of interference, but thanks, I will try all your suggestions to see if I can outpower them, at least in my home. Thanks!

atari7202 · 10th August 2006, 07:11 PM

i am trying to do that to. with my ipod transmitter i have all of the parts to make this http://hem.passagen.se/communication/pa313.htmlone but havent yet.
here is the main website it has tons of info that is very usefull http://hem.passagen.se/communication/pa313.html ooh and any body is it possiable to build a toy car amplifier {for the antenna go long distance} like frequeces like 45,27,49mhz to name a few

chiba · 11th August 2006, 12:54 AM

1.5W Amp on 88-108Mhz can get you in a big hot steaming bunch of trouble, I'm not sure what the EIRP limit is in your area but i think it's probably in µwatts, may be ok inside a fallout bunker if it's got lead lining.

Hero999 · 11th August 2006, 08:58 PM

Quote:

Originally Posted by HiTech

connect it to one leg of the AC wiring in your apartment, that way you'll use a majority of the wiring as an antenna. That'll do ya!

I know you're joking but it wouldn't work, all the power will go straight to ground.

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9th August 2006, 03:31 AM	(permalink)
juan123	FM transmitter antenna Well, I posted about modifying a tunecast FM transmitter. I added an antenna and the range has improved dramatically. Well my query is , how could I build an antenna that would not use too much space, but at the same time give me much more range than what I have now? My current antenna is just a 15ft long wire going up to the 3rd story of my house, from the 2nd story. I'd like to build an antenna that would boost my signal much more than that wire. I'm thinking maybe an electronic antenna that is powered?(If those exist.) I'm kind of a newbie with electronics, but I do know basics-intermediate level of electronics. Thanks for any help! BTW the FM transmitter is working at 88.1-88.7 mhz, if that helps at all to help you experts with the numbers. Thanks!!!!!!! __________________ Thanks! --Juan

9th August 2006, 04:12 AM	(permalink)
mister_e	I don't know in your country but i believe it's illegal to broadcast within this frequency range for long distance. FM modulator and cheap wireless microphone use it... but for few inches, feet. __________________ Steve ______________________ info@mister-e.org www.mister-e.org

9th August 2006, 11:17 AM	(permalink)
stevez	Juan - I'd encourage you to work within the limits of the laws. With that said I'll offer some information in the form of comments or statements. A. Some antennas radiate in all directions - some in specific directions. Directional antennas can provide a stronger signal in one direction (at the expense of other directions) with the same level of power. A beam or yagi beam can do that. B. A transmitter connects to an antenna directly or via a cable/wire called a transmission line. The transmitter output will be maximum when the transmitter is matched to the load - which is the antenna/transmission line. C. If the transmitter connects to the antenna via a cable/wire - a transmission line - one needs to consider that all of the power won't get to the antenna - some will be lost in the transmission line. The lowest losses occur when antenna and transmission lines match and the transmitter and transmission lines match. D. An amplifier could be used to increase the power output of the transmitter. E. Transmitters put out signals on the frequency of interest and other frequencies. Simpler transmitters are likely to be worse in this sense. A better antenna will radiate the stuff you want better - and maybe the stuff you don't want to radiate. The same is true for an amplifier - and it can generate it's own extra RF signals. I am sure this barely scratches the surface for you however it's not a simple subject. __________________ stevez

9th August 2006, 12:49 PM	(permalink)
HiTech	connect it to one leg of the AC wiring in your apartment, that way you'll use a majority of the wiring as an antenna. That'll do ya! __________________ Don't make me reach through this monitor to slap you a good one!

10th August 2006, 11:14 AM	(permalink)
stevez	Chiba's attachment shows a dipole. If kept clear of other conductive objects it will have a feedpoint impedance that will be an approximate match for 50 or 75 ohm cable. A common output impedance for transmitters is 50 ohms so this ought to be a good match. If all you have is 300 TV twinlead you can make that work with baluns (transformers) or you can just make sure you use integral odd multiples of half wavelength twinlead. Note that the wavelength must be the electrical wavelength for the cable - not in free space -or about 92% of the free space wavelength. This will essentially repeat the feedpoint impedance at the transmitter and provide a good match if it's 50 to 75 ohms. For line of sight communications polarization matters. If you orient the transmitter antenna horizontally then best reception will occur if the receiving antenna is horizontal and the same holds for vertical - transmitting antenna and receiving antenna should be vertical. A dipole can be mounted either way. __________________ stevez

10th August 2006, 01:31 PM	(permalink)
juan123	Thanks! Thanks, I will try all of your suggestions.....Recently I've been having some trouble bc a radio station operates at 88.1 , which is the frequency I use and there's other radio stations at 88.5, 88.9. My transmitter only works with : 88.1, 88.3, 88.5, 88.7...which would mean that I will have a lot of interference, but thanks, I will try all your suggestions to see if I can outpower them, at least in my home. Thanks! __________________ Thanks! --Juan

10th August 2006, 07:11 PM	(permalink)
atari7202	i am trying to do that to. with my ipod transmitter i have all of the parts to make this http://hem.passagen.se/communication/pa313.htmlone but havent yet. here is the main website it has tons of info that is very usefull http://hem.passagen.se/communication/pa313.html ooh and any body is it possiable to build a toy car amplifier {for the antenna go long distance} like frequeces like 45,27,49mhz to name a few

11th August 2006, 12:54 AM	(permalink)
chiba	1.5W Amp on 88-108Mhz can get you in a big hot steaming bunch of trouble, I'm not sure what the EIRP limit is in your area but i think it's probably in µwatts, may be ok inside a fallout bunker if it's got lead lining. __________________ 2.4Gigglehurtz