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hot to transmit this data???

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kahafeez

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Hi, i've been able to make an FSK circuit and its working good.....

now i've to send it in the air....... for wireless communication.... now the question is that if my FSK signal's low freq is 19MHz and hi freq is 20MHz (refer to the image i've attached, here i've kept a big difference in the hi and lo level freq so that it can be easily seen)....... now i've 2 questions:


1- do i simply have to put a power amplifier whose input would be the circuit in the image and then attach an antenna to the output of the power amp as 20MHz will cover atleast 10meters.... and i dont need much range..... plz reply refer to the image named 'power amp.jpg'

2- what does the power amplifier boost?? current or voltage?? plz guide me and if possible make a sketch of the block digram .....
 

Mazz

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The problem to inject a signal into an antenna comes up from the fact that antennas have tipically a low impedance (50 Ohm). So you'll need a circuit that is able to feed a proper POWER into antenna. The covered range depends not only on transmitted power but also on receiver sensitivity (minimum detectable signal).
Usually transmitters have power from -10 dBm to +20 dBm (it is a large range...).

So your problem can be solved like this:
-given 10m distance, calculate path loss at your working freq and add some margin (for example 30 dB loss +10 dB margin).
-given your receiver sensitivity (for example -60 dBm), calculate trasmit power at antenna (-60+40=-20 dBm)
-given antenna gain (for example 5 dBi), your power amplifier have to feed into antenna impedance -15 dBm.

I have done a very quick exercise, but I hope I've been clear enough to give you some guide line.

Mazz
 

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