Measuring SWR

If you want to just measure SWR, then you don’t need to measure RF power meter, then you can use a cheap meter and get adequate results. SWR only is only a relative measurement comparing power going out and power coming back. Given this is does not matter if the frequency response of the RF detectors in the meter are good or bad. Only the forward and reflected sensors need to be equal. If they are equally bad it will work, if they are equally good it will work. The main thing is that they are equal and this is usually the case. This type of meter will work fine for SWR only measurements.

low cost swr rf power meter for 88-108 mhz

Measuring RF Power

If you want to measure RF Power at 88 – 108 and SWR, then you cannot use cheap meters. If you need power sensors that have a flat and uniform response over the frequency range you are measuring. Cheap meters are available with the RF power function, but they will not indicate the correct power. You need to use something like this.

good quality rf power meter and swr meter for 88 108 mhz

Aareff RF Power

All our 100W transmitters and higher in power have a built in meter. On the front panel there’s a forward and reflected switch which allows you to measure the power actually going out to the antenna and if any is being reflected. You don’t need to use an external meter, but you can if you want. If there’s reflected power of between 10 and 15% of the full power, then there’s probably a problem with the connectors, or maybe the screen or ground on the coax where it enters the connector. It’s also possible the antenna has gone off tune a little due to the weather taking it’s toll. With our transmitters if the reflected power is between 15 and 25%, it usually means the cable or antenna somewhere in the line is completely open circuit, basically the signal disconnected somewhere or the exact opposite the signal is being shorted completely to ground.

By Paul Hollings

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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