# [SOLVED]NGspice Transmission Line Simulation

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#### fobos3

##### Newbie level 6
Hi,

I am trying to simulate a transmission line in NGspice but it doesn't seem to give me the expected results. I have a 2.3GHz ideal source with a 50 ohm internal resistance connected to one end of the transmission line. At the other end I terminate the transmission line at a 50 ohm load. The characteristic impedance is 50 ohm.

The simulation results give me a match at half wavelength, however, as I start decreasing the wavelength the voltage across the load starts decreasing and when I reach quarter wavelength it gives me Vout=0.

Any ideas? Here is my source code:
Code:
*.MODEL ymod txl R=0 G=0 L=341.8n C=136.7p length=15.9m
*Y1 Vin 0 Vout 0 ymod
T1 Vin 0 Vout 0 Z0=50 F=2.3G NL=0.1
Rout Vout 0 50

Rsource Vout Vsource 50
V1 Vsource 0 AC 1 sin(0 1 2.3G)
.control
tran 1000f 10n
plot Vout
.endc

Last edited:

#### h_vogt

##### Member level 1
Vout is a complex vector.

plot Vout
is
plot real(Vout)

Maybe you want to look at
plot mag(Vout)

Holger

#### fobos3

##### Newbie level 6
Vout is not a complex vector because it is tran analysis. Indeed, when I do plot real(Vout) or mag(Vout) it gives me the same results. Anyway, the weired thing is I get a decaying sine wave at Vout.

V

#### volker_muehlhaus

##### Guest
I think you should have both 50 ohm source and load impedance.

#### fobos3

##### Newbie level 6
I have 50 ohm source, load and characteristic impedance.

#### FvM

##### Super Moderator
Staff member
I have 50 ohm source, load and characteristic impedance.
No, you don't. I guess you meaned to write. Now you have a mismatched and unterminated transmission line.
Code:
Rsource [COLOR="#FF0000"]Vin[/COLOR] Vsource 50

fobos3

### fobos3

points: 2

#### fobos3

##### Newbie level 6
I feel stupid now. Thanks.

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