EMRFD Message Archive 7620
Message Date From Subject 7620 2012-07-17 16:06:27 Thomas S. Knutsen VHF Impedance tuner.
Recent experiments on dual gate pre-amps I have found an need for an type
of tuner that can match any point on the smith chart to 50 ohm.
Since I expect this to be impossible, I would be satisfied with matching
1K-3K ohms to 50 ohm.
Is it possible to use an L match? Would an L match let me move to any point
on the smith chart within those limits?
It should also be fairly easy to solve for what impedance it have at any
point, either with an microcontroller or with software in the PC.
The measurements are going to be done with an PC and control of the tuner
would be easy done with the PC, but I would like to avoid having to switch
to an network analyzer in order to measure the impedance of the tuner.
73 de Thomas LA3PNA/AE5YS.
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[Non-text portions of this message have been removed]7621 2012-07-17 16:28:35 Dean Blake Re: VHF Impedance tuner.
Wouldn't you be able to model your question into a spice program and test the L match
against various impedance ranges. If your just finding the conjugate of an impedance
range both with capacitive or inductive reactance and you solve for the LC values
of the match with the spice program that should give you the L Match components you need
K4DSB
Dean
To: emrfd@yahoogroups.com
From: la3pna@gmail.com
Date: Wed, 18 Jul 2012 01:05:46 +0200
Subject: [emrfd] VHF Impedance tuner.
Hello.
Recent experiments on dual gate pre-amps I have found an need for an type
of tuner that can match any point on the smith chart to 50 ohm.
Since I expect this to be impossible, I would be satisfied with matching
1K-3K ohms to 50 ohm.
Is it possible to use an L match? Would an L match let me move to any point
on the smith chart within those limits?
It should also be fairly easy to solve for what impedance it have at any
point, either with an microcontroller or with software in the PC.
The measurements are going to be done with an PC and control of the tuner
would be easy done with the PC, but I would like to avoid having to switch
to an network analyzer in order to measure the impedance of the tuner.
73 de Thomas LA3PNA/AE5YS.
--
Please avoid sending me Word or PowerPoint attachments.
See <http://www.gnu.org/philosophy/no-word-attachments.html>
PDF is an better alternative and there are always LaTeX!
[Non-text portions of this message have been removed]
[Non-text portions of this message have been removed]7622 2012-07-17 17:18:31 Nick Kennedy Re: VHF Impedance tuner.
I'm accustomed to using the L match to transform a pure resistance. An L
section can lower a resistance greater than 50 ohms to 50 with the shunt
element. The series element then is used to cancel the residual reactance
from the shunt element.
Hmm ... so if you have a complex impedance to start with, you'd first add a
series reactive element to cancel the reactive part, then do the
traditional L match. But that only works with the residual real R > 50 in
your case. The L-network can be used "backwards", but that would mean
reconfiguring your circuit.
You should download SimSmith and play with the possibilities.
73-
Nick, WA5BDU
> Since I expect this to be impossible, I would be satisfied with matching[Non-text portions of this message have been removed]
> 1K-3K ohms to 50 ohm.
> Is it possible to use an L match? Would an L match let me move to any point
> on the smith chart within those limits?
>
>
>
> 73 de Thomas LA3PNA/AE5YS.
>
>
>
7623 2012-07-17 18:25:13 RW Mail List Re: VHF Impedance tuner.
You can see for yourself what a L matching circuit can do with an excellent smith chart program called “Smith”.
http://www.fritz.dellsperger.net/
Using the “keyboard”, enter the frequency and impedance you want to match.
Then select a component to get onto either;
(1) the red series matching circle, then select a series component that will take you to the 50 jo ohm Zo point.
Or
(2) the blue parallel matching circle, then select a parallel component that will get you to the 50 j0 ohm Zo point.
The matching circles are the blue and red thick line circles that run through the 50 j0 ohm Zo point.
The Default Zo can be set to any impedance that you want to match to by going to “Extra”, “Settings” menus. If you can’t see the Z-plane or Y-plane (the red and blue Matching circles), then select them by going to the “Extra”, “Settings” menus.
“Smith” will also give you the circuit and component values.
I don’t know where I would be without the Smith Chart.
Regards,
Roderick Wall, vk3yc.
7624 2012-07-17 22:17:28 victor Re: VHF Impedance tuner.
I posted there a picture that shows exactly what are the impedance that each L network can match.
Victor - 4Z4ME