https://www.aareff.com/en/250w-erp-fm-transmitter-system.htm

By Michael Campos
https://aareff.com/michael-campos.htm

Community radio also known as LPFM in the USA which stands for LOW POWER FM was created to provide a non expensive method for non profit groups to get on the air operating anywhere from 1w – 100w. This attempts to bring humanity together, induce creativity in individuals and transform communities by having their own people RUN and PRODUCE their own programs. This gives sufficient time to elaborate programs which bring interest to the community. One of the reasons for this sufficient time is that generally community radios are legally PROHIBITED or RESTRICTED to play any sort of advertisements opposed to commercial radio.

To the best of our knowledge the first known community radio was introduced in 1940 in Bolivia during a labor strike, since then it’s become an essential tool for communities to fulfilling the urge, the desire for communication and self expression.

Community Radio in some countries is not protected from interference that may be received, unlike commercial radio. Also it’s sponsored by individuals and business that believe in the concept of giving a voice to the rarely heard while giving us the freedom of speech thought and expression.

On the other hand commercial radio is based on business on the practice of airing radio advertisements for profit. Commercial radios mostly owned by private corporates and are known for playing high quantities of copyright music with a high ratio of advertisements cutting short the time for community programs and local issues.

Things You Didn’t Know About Commercial Radio

1.In most stations DJ’s don’t pick the music, the management do this.
2.Your production must be very professional or it won’t be played.
3.Buying advertisements and trading publications is not required but helpful.
4.It’s not about if your music is good or not, it’s about ratings.

In conclusion, community radio was created to give people of the community an opportunity to express themselves in a with truth and honesty in way that cannot be done with commercial radio.

You can have the biggest and the best FM transmitter in the world, but if the power doesn’t get from it to the antenna you may as well turn it off. A transmitter is only as good as the antenna it is connected to. A poorly tuned antenna and antenna cable will send the power back to the transmitter and in worse case cause it to over heat resulting in permanent damage. It’s a bit like driving a car with flat tyres, it will move slowly, but most of the power will be used in chewing the wheel rims to pieces. A well tuned antenna will take all the power put into it and radiated it all into free space. The antenna is effectively a transformer between the transmitters RF electrical current and free space.

The term SWR is used to measure the performance of an antenna.SWR is short for Standing Wave Ratio. An SWR of 1:1 indicates that the antenna is perfectly matched and there’s no reflected power. At the other end of the scale an SWR of 1:Infinity indicates that no power is being absorbed by the antenna and all the transmitter power is being reflected back to the transmitter.

A useful piece of test equipment that measures SWR is an SWR meter. All serious radio stations should have one of these. This connects in line between the transmitter and the antenna and antenna cable. SWR meters have a switch on them usually labeled up as FWD and REF. In the FWD position the meter indicates the forward power traveling on the antenna cable, this is the power going from the transmitter to the antenna. In the REF position the meter indicates the reflected power traveling on the antenna cable, this is the power that has not been absorbed by the antenna returning back to the transmitter. To make an SWR reading the transmitter is switched on, the meter is set to FWD position and the CAL control is turned to make the meter needle point to 100%. The SWR meter is then set to REF position, the reading shown on the meter is the amount of reflected power relative to the forward power.

Significance of the SWR reading.
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Why use your limiters? the bigger nice looking 19 inch rack limiters from Behringer and other similar brands are the same price?

For FM broadcasting the attack has to be very fast at all audio frequencies, audio above 15KHz should be cut and pre-emphasis has to be applied before limiting.The commercial 19 inch rack mount type limiters, compressors and audio processors that are for bands, discos and recording studios don’t do this.

Our limiters do not use any digital sampling, they are high quality, low distortion, low noise and analogue design, perfect for FM transmitters.

Our limiters start to cut off sharply at around 14 KHz using a Salem and Key active filter. The commercial 19 inch rack mount type work up to 20KHz and way beyond, in the applications they are designed for this is okay and there’s no reason to cut the frequency above 15 KHz. They are not designed for FM transmitters
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