Mono, MPX, Stereo, Compression, Limiting, Processor, RDS. Which one do I use? Which one do I need?

By Yoneli J
https://aareff.com/yoneli-jimenez.htm

FM Transmitter Mono/MPX Version.

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Stations with more engineering experience may use this version, this is because it does not include limiting or stereo coder circuitry. The audio limiting for this version must be externally provided and in accordance with the recommendations of http://www.aareff.com/ETR132.pdf. This version is typically used with external multi band processors, stereo generators and RDS generators such as the brands Orban or Inovonics. Not recommended for novice stations or beginners.

FM Transmitter Stereo Version.

This is similar to the Mono/MPX version except it is stereo and RDS cannot be used with this. Again stations with more engineering experience may use this version, this is because it does not include audio limiting. Again the audio limiting for this version must be externally provided and in accordance with the recommendations of http://www.aareff.com/ETR132.pdf. This version is typically used with external multi band processors and stereo generators such as the brands Orban or Inovonics. Not recommended for novice stations or beginners.

FM Transmitter Stereo Version with Audio Compression and Limiting.

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Most small radio stations and beginners will use this version, this is because it includes audio processing circuitry and suitable limiting to keep the transmitter in compliance with the maximum bandwidth permitted by the international regulations. There is also access to the MPX in and out on the back panel which allows all known RDS units to be connected. Novice stations with limited experience of FM broadcasting transmitters should purchase this version.

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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