What does it meant 50 Ohm input and output in LNA circuit

Dodgydave

Joined Jun 22, 2012
11,285
It's an RF wideband amplifier, it needs a 50 ohms cable input and output to produce a maximum signal with minimal signal loss,..
 

MrChips

Joined Oct 2, 2009
30,720
50 ohms in this case is in reference to the impedance of the coax cable to be used.

The most common 50-ohm cable is RG-58/U. The designer of the circuit is suggesting that you use this cable or similar when connecting to the input and output of the Low Noise Amplifier (LNA).

Matching the impedance of the coax cable to wide-band broadcast equipment is essential if you want to preserve the integrity of the signal.
 

Thread Starter

dante_clericuzzio

Joined Mar 28, 2016
246
50 ohms in this case is in reference to the impedance of the coax cable to be used.

The most common 50-ohm cable is RG-58/U. The designer of the circuit is suggesting that you use this cable or similar when connecting to the input and output of the Low Noise Amplifier (LNA).

Matching the impedance of the coax cable to wide-band broadcast equipment is essential if you want to preserve the integrity of the signal.
Thank you very much this answer exactly what i wanted to know. Thanks again..

BTW does that meant some which require 30 Ohm or 100 Ohm also meant that we need to find coaxial cable with that specified impedance?
 

MrChips

Joined Oct 2, 2009
30,720
Thank you very much this answer exactly what i wanted to know. Thanks again..

BTW does that meant some which require 30 Ohm or 100 Ohm also meant that we need to find coaxial cable with that specified impedance?
The answer is yes.

30Ω is not common. The most common are 50, 75 and 100Ω (or 92Ω).
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In reality, you are trying to connect unit A to unit B. Unit A and unit B should have the same impedance and you would connect them with the same impedance cable, for example, 50Ω.

If unit A and unit B do not have the same impedance then you have a mismatch. You then have to look for ways to match the impedance.
 

MrAl

Joined Jun 17, 2014
11,396
Hi,

I dont think it is just the cable though, it's that the entire system should be 50 ohms.

For example, if you connect a 50 ohm type cable to the input and you are using an antenna on the input, then the antenna that connects to the other end of the cable should also be 50 ohms. If you somehow connected the antenna right to the input though, it should be a 50 ohm antenna or at least have a matching network that converts the antenna impedance to the 50 ohm input impedance of the amplifier.

Same goes for the output. Regardless what it connects to, the cable and load should be 50 ohms. Output mismatches cause signal power loss and can even cause some amplifiers to blow out.
 

Papabravo

Joined Feb 24, 2006
21,159
On a deeper note it means that at the particular frequencies of interest the input impedance is 50 Ω and the output impedance is 50 Ω. This cannot be measured with a DC ohmmeter, this is an AC impedance, dependent on frequency, whose magnitude is 50 Ω.
In particular the actual value might be 50 + j0 or 40 + j30 or any other complex number with a magnitude of 50 Ω.
 

Thread Starter

dante_clericuzzio

Joined Mar 28, 2016
246
Thanks all i will with 50 Ohm coaxial and see how it goes. and the reason i asked about 30 ohm is because i have one mini portable radio that says the output impedance 30 ohm i am not sure exactly what it that was meant.
 
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