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Transmission line

 
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btb4198
Antenna Theory Regular


Joined: 19 May 2011
Posts: 20

PostPosted: Sat May 21, 2011 1:27 pm    Post subject: Transmission line Reply with quote

If a transmission line has a length greater than about 10% of a wavelength, then it will affect the circuit.

My antenna L is 0.03125m + .7m of more wire ( I may not have that much wire ) from the transmitters line. Than

L = 0.0315m + .7m = 0.7315m
λ = 0.125m

L is not >> λ so there is no transmission line problems.
Does this mean there is no Impedance Matching problems aswell?
Is Impedance Matching part of transmission line affect ?
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admin
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Joined: 03 Jan 2007
Posts: 197

PostPosted: Sat May 21, 2011 6:03 pm    Post subject: Reply with quote

You write
1) "If a transmission line has a length greater than about 10% of a wavelength, then it will affect the circuit. "

[which is true, and means L will affect the circuit if it is >0.1*lambda]. Then you write:

2) L = 0.0315m + .7m = 0.7315m
λ = 0.125m

So L > 5*lambda. Then you say:
3) "L is not >> λ so there is no transmission line problems."

How is your statement 3 compatible with your first statement? You're not posting coherent questions.

To answer your last two:
Transmission lines add to impedance matching complexity, but don't remove it. THat is, if you connect a radio directly to an antenna with a very short transmission line, you still have to worry about impedance matching. Transmission lines can complicate impedance matching.

However, if you are using an RF cable, it is probably rated at 50 Ohms (matching the receiver), which means you won't have to worry about the transmission line.

For your application, I'd recommend experimenting with your setup until you get something that works. I don't think you'll need to do impedance matching.
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btb4198
Antenna Theory Regular


Joined: 19 May 2011
Posts: 20

PostPosted: Sat May 21, 2011 6:44 pm    Post subject: Reply with quote

L = transmission line + the antenna's length..
L is the over all Transmisson line length...

Should you not add the antenna's length to the over all transmission line's length?
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btb4198
Antenna Theory Regular


Joined: 19 May 2011
Posts: 20

PostPosted: Sat May 21, 2011 6:49 pm    Post subject: Reply with quote

the impedance for the 2.4GHz transmitter I am using is 50Ω. I was going to just use a copper wire to wired the transmitter to the antenna. Do I have to worry about the impedance of the copper wire ?
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