Problem With My First FM Station
I decide to built my FM station , so i buy this kits from ebay
http://www.ebay.com/itm/Latest-Ver-8...item45fde7f2c2
and this antenna
http://www.ebay.com/itm/FM-Dipole-Br...item2a062c7c0c
i thought it was easy to build it, but i have face many problems. my frequency band was 103.5,
my first problem was the correct size of antenna arm . some website wort in calculation it's 58.5 cm or
69.2 cm. (( and because of the wrong size in the arm and the freq the system keep alarm for the antenna , (check you antenna )
some time i play with the arm & gamma size and frequency regarding to some website calculation . the heat keep raising slowly and ones i raise the rf power the heat alarm keep shown. the testing cable was 8 meters rg58 . the antenna was in my room also not up .
i have read many website talking about the FM Broadcasting , and i have discover many thing that is related to my problem .
1-the frequency & antenna size
2-size of gamma ( small arm)
3-type & size of cable
4-the high of antenna
5-type of antenna position (v or h )
## one thing the system is connected directly with antenna . with no coils in antenna
My goal is to built this system . using any frequency . any antenna to reach 300 w fm broadcast .
Many Thanks
First of all, the antenna that you bought is not omnidirectional, and I don't know if this is good for broadcasting.
Second, I would recommend instead using a dipole to use a collinear vertical antenna, which gives you some gain over a dipole, and also omnidirectional pattern.
The one below doesn't need any matching tuning, just plug the 50 ohms coax cable from your transmitter.
http://www.zcg.com.au/Catalogue/02-G12HP.pdf
Thats an excellent antenna example vfone, ideal for the OP's transmitter
just had to bookmark that one :)
to the OP, with anything over 1W of transmit power, I hope you have your station transmitting licence sorted out before you go on the air :)
cheers
Dave
Your antenna has horizontal polarisation , this is not often used in FM broadcasting except in high density areas or for special mixed polarisations .
I would not recommend a collinear antenna , as it has a very small bandwidth , once you are willing to change your frequency you need another antenna .
Second a collinear antenna is quite large and has a higher windload .
I would recommend a broadband dipole covering the whole FM band http://www.lambdaanttech.be/pdf/antennas/LATBD108.pdf this antenna is being side mounted on a pole or on a tower , it has 2dB gain over a single dipole and almost omnidirectional .
An antenna with a gamma match tuning needs to be tuned with a reflector and being mounted outside at at least 3-4m height . Tuning it with a VSWR meter is very timeconsuming , to tune the antenna you need a VNA where the Z value can be readed and then tuning the match unitl you reach approx 50ohm resistance and a reactance value as low as possible . Keep in mind if using a VNA that the cable being used is also being calibrated !
Good luck,
Kenny
When you get a license for an FM channel in 88-108 band, you get for ONLY one frequency.
So, doesn't matter too much the bandwidth of the antenna. Nevertheless the above manufacturer mentioned in the datasheet that they can provide antennas for any of frequencies in the band.
Collinear antennas are in used for FM transmissions by most of low power broadcasters, mainly due to its gain over dipole. 3dB antenna gain means double of the radiated power.
Vfone , yes your right about frequency , altough it can happen that the regulator decides to move on to another frequency .
I more recommend a broadband antenna for hobby radio stations as you never know what happens in the future .