Replace an antenna by an antenna+amplifier

[Butter]

Hi
Is it equivalent to replace an antenna of gain 10 dBi by an antenna of gain 5dBi with same bandwidth+ one 5 dB gain amplifier? How would the transmitted signal be different in those 2 situations in terms of power? and what else would be different?

 

[SLK001]

If the patterns are the same, then the transmitted signals would be basically the same. But why would you want to do this? This is like hooking up your car to a team of horses. You accomplish the same thing (transportation), but at much greater effort.

 

[Butter]

sorry, but I did not understad your explanation. What do you mean by if the patterns are the same? Do you mean that the transmitted signal would be the same from those 2 cases (power and radiation pattern)?

 

[BigBoss]

Hi
Is it equivalent to replace an antenna of gain 10 dBi by an antenna of gain 5dBi with same bandwidth+ one 5 dB gain amplifier? How would the transmitted signal be different in those 2 situations in terms of power? and what else would be different?

The first solution ( using 10dBi antenna ) is better because using an extra amplifier will decrease the S/N ratio.

 

[Butter]

The first solution ( using 10dBi antenna ) is better because using an extra amplifier will decrease the S/N ratio.

I wanted to know if the radiation pattern and the tranmitter power would be similar in those 2 cases? But following BigBoss reply, I would also like to know if it's only the S/N caractherictic that would change and how mush would it decrease, a little or a lot ? and which antenna and amplifier parameters would cause the S/N ratio reduction?thanks

 

[FvM]

The question isn't clear. Are you asking about receiver or transmitter operation?

 

[Butter]

The question isn't clear. Are you asking about receiver ...

As I mentioned I am interested to know if it's right that their transmitted power would be the same and that their radiation pattern could be similar in the case when both are directional antennas and their system output is 10 dBm ( 10 dBi for the first case and 5dBi + 5dBm =10 dBm output for the second) . So I am interested by the transmitter operation.

 

[betwixt]

In a transmitter scenario, given an equal radiation pattern, the ERP would be the same but obviously not the RF power. In a receiver scenario, the signal level would be the same but the SNR would be degraded by the amplifier.

In both cases, it would be unlikely the radiation/sensitivity pattern would be the same betwen a 5dbi and 10dbi antenna.

Brian.

 

[BigBoss]

The question isn't clear. Are you asking about receiver ...

As I mentioned I am interested to know if it's right that their transmitted power would be the same and that their radiation pattern could be similar in the case when both are directional antennas and their system output is 10 dBm ( 10 dBi for the first case and 5dBi + 5dBm =10 dBm output for the second) . So I am interested by the transmitter operation.

I presumed that your system is a receiver.
Nevertheless my statement is correct, using an amplifier with an antenna will practically not change too much at receiving side of the system.

 

[Butter]

In a transmitter scenario, given an equal radiation pattern, the ERP would be the same but obviously not the RF power. In a receiver scenario, the signal level would be the same but the SNR would be degraded by the amplifier.

In both cases, it would be unlikely the radiation/sensitivity pattern would be the same betwen a 5dbi and 10dbi antenna.

Brian.

Thanks. Since, the RF power would be smaller in a case (5 dBi amplifier + 5 dBi antenna), what would be the advantage of putting an amplifier with a 5 dBi antenna vs not including it with a 5 dBi antenna? How much does the 5 dBi amplifier improve the RF power?

 

[FvM]

I hear misunderstandings in your post.

I presume, you are comparing antennas without internal losses. And the objective is to achieve a specific field strength at a receiver location in the antenna's principal direction.

To compensate for the lower directivity of the 5 dBi antenna and achieve the same field strength as with the 10 dBi type, you need to raise the antenna input power by 5 dB. That's the purpose of the 5 dB amplifier.

 

[Butter]

I hear misunderstandings in your post.

I presume, you are comparing antennas without internal losses. And the objective is to achieve a specific field strength at a receiver location in the antenna's principal direction.

To compensate for the lower directivity of the 5 dBi antenna and achieve the same field strength as with the 10 dBi type, you need to raise the antenna input power by 5 dB. That's the purpose of the 5 dB amplifier.

I need to have the same power received by the receiver from the transmitter antenna and not specificaly the same field strength. So that's why I would like to know if an amplifier would do the job? betwixt said that the received rf power would be different and I didn't understand why?

 

[volker@muehlhaus]

betwixt said that the received rf power would be different and I didn't understand why?

The antenna with higher gain can better "focus" the power to one direction, so that you have more power in that direction, and less power in other directions.

 

[FvM]

I need to have the same power received by the receiver from the transmitter antenna and not specificaly the same field strength.

Received power is field strength multiply antenna factor. So if you have the same receiver antenna in both cases (you didn't specify anything about it), field strength at the receiver location and received power are just the same thing.