matching antenna to transistor amplifier - RF Cafe Forums

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bamatom
Post subject: matching antenna to transistor amplifier
Posted: Thu May 18, 2006 10:00 am
 
Lieutenant

Joined: Thu May 18, 2006 9:46 am
Posts: 3
I have a general question how to match an antenna to a self designed transistor amplifier. I want to use a 2N4427 for 100MHz in common emitter configuration (emitter directly on ground). The collector is connected to 12V with via an inductor with a high inductance. If I take the signal at the emitter, what output impedance do I see? Is there a rule of thumb how to deal with the transistors regarding to power matching. If I look at the VSWR or S-Parameter of my antenna, there is also a complex part. When everyone talks about output impedance of the transistor, there is always only a real number of Z mentioned. Is there no complex part?

I guess this is a very simple question and I am just confused. However, an answer would very much help me to understand the whole antenna matching to an amplifier topic better.

-tom
 
 
Dexter
Post subject:
Posted: Tue May 23, 2006 1:58 pm
 
Captain
User avatar

Joined: Thu May 04, 2006 7:37 am
Posts: 7
Hello Mr. Bamatom,

Your questions about transistor are very basic, and are covered quite well by the well-known Mr. Randy Rhea, in the last two editions of High Frequency Electronics. Here is the path for the 1st one. You can find the other on HFE website.

http://www.highfrequencyelectronics.com ... 6_Rhea.pdf

The simple answer to your question is that, yes, for an amplifier (transistor) that has not already been matched to 50 ohm, there will be both a real and an imaginary part. Truth is, even with a "50 ohm" device, it is almost certainly not purely resistive. Read through Randy's two articles and you'll have amuch better understanding, I guarantee you.

Dexter
 
 
liw003
Post subject: Re: matching antenna to transistor amplifier
Posted: Sat May 27, 2006 8:03 pm
 
Lieutenant

Joined: Sat Apr 15, 2006 10:13 pm
Posts: 1
I am curious why you try to find the output impedance looking from emitter since you use it as common emitter. For me, I would care how to match the base and collector port. Why VSWR is a complex number? It should be the Amplitude of maximun voltage value over minimun voltage value. I don't know where is the complex part come from. And the reason why S-parameter is complex value is that amplifier has equivalent capacitance in side. S-parameter is define to descript the intrinsic properties of a box. Now the box is instead of an amplifer.

bamatom wrote:
I have a general question how to match an antenna to a self designed transistor amplifier. I want to use a 2N4427 for 100MHz in common emitter configuration (emitter directly on ground). The collector is connected to 12V with via an inductor with a high inductance. If I take the signal at the emitter, what output impedance do I see? Is there a rule of thumb how to deal with the transistors regarding to power matching. If I look at the VSWR or S-Parameter of my antenna, there is also a complex part. When everyone talks about output impedance of the transistor, there is always only a real number of Z mentioned. Is there no complex part?

I guess this is a very simple question and I am just confused. However, an answer would very much help me to understand the whole antenna matching to an amplifier topic better.

-tom



Posted  11/12/2012