## help using linsmith

2005-11-30
2012-12-12

• daniel sawyer
2005-11-30

I have the following questions regarding the use of linsmith:

How are sources generated?

What is the difference between a load and a circuit?

Can a load at the end of a transmission line be calculated by the impedance measured at the other end? i.e. at the source end?

Sorry to be so basic. Thanks Dan kb0qil

• John Coppens
2005-11-30

• daniel sawyer
2005-12-01

Thanks for pointing to those documents. Unfortuately they do not answer the questions. That response does not answer the questions. Let me try again:

1. What is the electrical equilivant of a 'load'. Is it truely a load in the context of a passive element or does it have some other representation?

2. I would like to model a complex load at the end of a transmission line. The only evidence available is the value of the reflected component, i.e. voltage and phase. If the value of the transmission line and the source is known can the impedance value of the unknown load modeled?

I am stuck on the electrical circuit equilivant description of a load? I do not understand how any circuit can have a response without a source. Is this a difference in understanding of the terms source and load?

Thanks - Dan kb0qil

• John Coppens
2005-12-01

1) What is the electrical equilivant of a 'load'.

A load, in transmission line matching terms, just an electrical impedance, which represents the characteristics of that load. It is not comparable with a 'model' like in SPICE, for example. A load is normally defined as a complex impedance, eventually defined at several frequencies.

2. I would like to model a complex load at the end of a transmission line.

I suspect that you want to _determine_ the load impedance (evt at several frequencies) when the impedance at the other end of the line is known. Using a normal Smith chart you would do that inverting the movements on the chart (rotate CCW, eg). This is not yet easy to do on linSmith.

I tried to avoid this because of possible confusion, and because maybe 80 or 90% of the problems are inverse... But I will add this later. It would be useful if using, for example, a noise bridge or vector analyzer at the source end of the cable.

Thanks for the msg.
John

• daniel sawyer
2005-12-01

Thanks for the reply. Yes, I am trying to determine antenna characteristcs by measurements taken in the shack.

I have a couple of basic questions:

1. I set up linsmith with a 'load' of 4 mhz and 50 ohms. I then set up a parallel circuit of an inductor.

The impedance seemed to behave inversly. As its value was increased the impedance on the chart went closer to 50 ohm.

2. However if I changed the configuration to serial it behaved as I would expect.

What am I missing?

Thanks - Dan kb0qil

• John Coppens
2005-12-01

Dan,

That seems quite logical. If you put an inductance in parallel, its influence decreases with its value = the larger the inductance, the larger the reactance, the less influence it has on the 50 Ohm load.

In fact, this is exactly one of the reasons why I think the Smith chart is useful!

John