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Selecting amplifier power level for generating field strength

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spirited09

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I am trying to determine the power level I should be using in a amplifier for generating an electric field at a distance . For example to generate 30V/m@ 1m until 1GHz.

I have considered cable loss , antenna gain, VSWR mismatch at antenna and air loss to obtain the required power needed in the amplifier.

However the value obtained is a gross underestimate to actual results , hence would like to know if there is anything else that i missed out that result in this error?

Thanks
 
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jiripolivka

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In actual operation, the EIRP at the antenna is important as well as antenna radiation pattern close to ground. Also the receiving antenna pattern is important.

The "air loss" or propagation loss , depends not only upon the distance but also on the distance from a (lossy) ground, if there is a vegetation or obstacles along the line of sight, etc. Apply the rule of Fresnel zones if you have such obstacles around.

In general, calculating the line budget for a satellite radio link is easier than for a terrestrial link. In a real situation, surprises do happen.
 

davenn

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In actual operation, the EIRP at the antenna is important as well as antenna radiation pattern close to ground. Also the receiving antenna pattern is important.

The "air loss" or propagation loss , depends not only upon the distance but also on the distance from a (lossy) ground, if there is a vegetation or obstacles along the line of sight, etc. Apply the rule of Fresnel zones if you have such obstacles around.

In general, calculating the line budget for a satellite radio link is easier than for a terrestrial link. In a real situation, surprises do happen.
you did notice he said at 1 ( ONE) metre ?
any of your link budget programs and other commented parameters are not going to work over such a short distance

Dave
 

jiripolivka

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you did notice he said at 1 ( ONE) metre ?
any of your link budget programs and other commented parameters are not going to work over such a short distance

Dave
Thank you, I did not notice the one meter distance! At 1 GHz, 30 cm wavelength, even with simple dipoles, one operates in the "near zone". This results in an interference - moving one of the antennas along the line will cause huge changes in transmitted power. Difficult to calculate, and ground will contribute,too.

Instead of modeling, make an experiment to see what happens!
 

FvM

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Without seeing your calculation, I don't want to guess finally about the problem. Although 3λ is near field, the field strength won't be be very different from far field value according to Friis equation, presumed you are using simple antennas (e.g. a dipole) and don't have strong reflections.
 

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