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Does antennas work in two-ways ??

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halt

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hello
sorry it's a stupid question but i just need to know does a receiving antenna can work as a transmitting antenna ?
 

electronics_kumar

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halt said:
hello
sorry it's a stupid question but i just need to know does a receiving antenna can work as a transmitting antenna ?
since....simply it follows reciprocity theroem....
 

    halt

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halt

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thanks guys for your help
 

albert22

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In theory the antenas are reciprocal. They can be used to transmit and receive.
But in the real world, some antennas are designed just for receiving.
To transmit with an antenna, its impedance should be matched to the transmission line and that of the transmitter. That is SWR 1:1 or as low as possible. A mismatch in a receiving antenna is not a major issue.
The other thing that you must be aware of is the power ratting of the antenna. Some receiving antennas could be used for transmitting only with very low power (QRP).
Another issue is efficiency. an antenna (like a small loop) could work very well to receive but its efficiency is very poor (as the diameter decreases).
Active antennas (an antenna with a preamplifier) cannot be used to tx unless you switch out the preamp.
Verticals, Dipoles, yaguis and similar antennas are very close to the theory and are
are used with transceivers for transmission and receiving.
 

Dr_mas

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hi
i agree with the previous replies that the antenna can be used as transmitter or reciever
and i would like to add that its recieving pattern is the same as the transmiting pattern.
mas
 

pmonon

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And, there is a new generation of antennas coming up and that is: intelligent!
 

Dr_mas

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hi pmonon
do you mean the smart antenna?

mas
 

kvn17

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hi albert22,

why is the matching at antenna/receiver not as important as antenna/transmitter?

thanks,
kvn
 

ramy gad

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because in the trasmitting antenna we have large power if we did not match the antenna the reflected power can burn the transmitter or the transmition line
 

albert22

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As ramy gad said, a mismatch between the antena and the transmitter could cause damage. Modern transceivers have a protection circuit which reduces the power when there is high SWR (mismatch).
All stages in a RF circuit should be matched otherwise the power is not transfered efficiently. And there might be other consequences too. For example a filter impedance should be matched at its input and its output. If not the filter will not work properly, its frequency responce will surelly be distorted.
Receiving antennas are no exception to matching but in most cases there are no practical consecuences. In very special cases an antenna preamplifier could oscillate if there is a mismatch on the antenna but only when the amp is inestable.
When you operate a transceiver with a dipole you will have good reception on a wide range of freq. (even on other bands the Rx will be ok) but the transmition will only have low SWR on a narrow band.
 

a.mal

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Yes if antenna were reciprocal .
 

pmonon

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Generally, they are
 

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