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Some doubts related to wireless signal transmission.

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vinodstanur

vinodstanur

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hi
Could any one explain how could i transmit a 10Mhz signal without any inductor coils or tank circuits...
I got this doubt just after hearing about coilless FM transmitter. So how coilless fm transmitter works? If i connect the output of a microcontroller which works as an astable multivibrator at 5Mhz to a long antenna, then will it transmit that 5Mhz frequency to air? And could i detect it from a distance of about 100 meters?
 

It is possible. you will have peak to peak voltage of perhaps 3v, which is around 1v rms, which is around 10-20 milliwatts. If you hook that to a quarterwave antenna (15 meters long wired), you will have a detectable signal -20 dBm or so, assuming 0 dBi antenna gains) at the distance:

Intelligence Support Group, Inc. - Free Space Path Loss Calculator

That is an easily detectable signal. The problems are:

1) those are really long antennas, if you use shorter ones the gain will drop dramatically
2) you will be transmitting a lot of harmonics, which should be lowpass filtered out.
 
Expanding on what biff44 states, a square wave, as found on the pin of a logic device will be VERY rich in harmonics. Although some of the power will be at the frequency you generate in software, an appreciable amount will be at harmonics and could cause interference to other users.

I think you will find coilless transmitters usually use a different method of setting their frequency such as using ceramic, quartz or SAW resonators.

Brian.
 

The "coilless" aspect can be understand in different regards, I think.
- The transmitter is not using a magnetic antenna, which would be an option at least for 5 or 10 MHz.
- It does without any LC filters. Filters are usually required to keep the RF regulations for harmonic transmission. A 5 or 10 MHz transmitter must ignore these requirements anyway.
- It's not using LC elements for antenna impedance matching, so the efficiency will be possibly poor.
But apart from these considerations, it can work of course.
 

if i take a 10Mhz or 20Mhz sinewave from a function generator, then what should i do to transmit it to atmosphere using a telescopic antenna used in fm radio?
 

Optical transmitting can be alternative for short distance..
For instance with ..Infrared diodes
 

Actually its an example, i want to know how it could be transmitted via telescopic antenna, i mean what extra circuitry should be introduced to couple that 10Mhz signal to a telescopic antenna? And what exactly is happening in that antenna? How it generates EM waves?
 

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