VHF (and a little HF) PA impedance matching
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Re: VHF (and a little HF) PA impedance matching
Thanks very much, Harry.
I now feel much more confident than with my previous method, ie guess plus trial and error. I will try putting it into practice this coming weekend.
Cheers,
Steve
I now feel much more confident than with my previous method, ie guess plus trial and error. I will try putting it into practice this coming weekend.
Cheers,
Steve
Re: VHF (and a little HF) PA impedance matching
Hi Ivan, I am so glad you like it.
I thought that this info was already freely available on the web but when I began to study some of them I found loads of basic errors with the formulas they published.
As a matter of interest, my "rule of thumb" is to choose a Q of 2 and then take two caps in the PI filter:
Zc1 = Transistor output impedance
Zc2 = wanted output impedance
Zl1 = Zc1 + Zc2
That will resonate at the frequency of interest and have a very wide response. It makes a very easy target to hit with hand-wound coils and can almost be worked out on your fingers (I hate maths). For higher Q one can 2x Zc1 & Zc1 but 0.5x Zl1. For practical purposes this is adequate.
But I am so glad you liked the article.
BR Harry
I thought that this info was already freely available on the web but when I began to study some of them I found loads of basic errors with the formulas they published.
As a matter of interest, my "rule of thumb" is to choose a Q of 2 and then take two caps in the PI filter:
Zc1 = Transistor output impedance
Zc2 = wanted output impedance
Zl1 = Zc1 + Zc2
That will resonate at the frequency of interest and have a very wide response. It makes a very easy target to hit with hand-wound coils and can almost be worked out on your fingers (I hate maths). For higher Q one can 2x Zc1 & Zc1 but 0.5x Zl1. For practical purposes this is adequate.
But I am so glad you liked the article.
BR Harry
_________________
Everything in this world is either bacon, or it isn't bacon
They say that money cannot bring you happiness, but if you have it then you can always buy more bacon
Re: VHF (and a little HF) PA impedance matching
Very nice article, Harry !
MNI TNX
VBR from Ivan
MNI TNX
VBR from Ivan
Ivan- Posts : 796
Join date : 2012-11-25
Age : 64
Location : Praha, Czechia
VHF (and a little HF) PA impedance matching
I have had a little less stress for a couple of weeks and an my travels I found the time to sit on a plane and do a little drawing. I just happen to have a copy of my old PYE training notes with me on the computer, so I though I would share a little information.
I have had recent(ish) requests for transistor impedance matching and FET, but now I have taken care of the first. I wanted to add on-line formulas but I did not have internet access on the plane and I could not remember the JAVA script. I may get-a-round-twitt sometime soon, but in the meantime here you have the formulas. I shall be uploading the Motorola AN file quoted to the homepages, but I will not post my PYE course notes.
Anyway, have fun. Here is the link:
http://www.sm0vpo.com/blocks/transistors_match_00.htm
Finally, I must point out that I use simplified but less accurate formulas today that allow me to work out roughly the right area without having to take off my socks. All I need is my fingers. But this document gives you a good starting point.
Best regards from Harry - SM0VPO
I have had recent(ish) requests for transistor impedance matching and FET, but now I have taken care of the first. I wanted to add on-line formulas but I did not have internet access on the plane and I could not remember the JAVA script. I may get-a-round-twitt sometime soon, but in the meantime here you have the formulas. I shall be uploading the Motorola AN file quoted to the homepages, but I will not post my PYE course notes.
Anyway, have fun. Here is the link:
http://www.sm0vpo.com/blocks/transistors_match_00.htm
Finally, I must point out that I use simplified but less accurate formulas today that allow me to work out roughly the right area without having to take off my socks. All I need is my fingers. But this document gives you a good starting point.
Best regards from Harry - SM0VPO
_________________
Everything in this world is either bacon, or it isn't bacon
They say that money cannot bring you happiness, but if you have it then you can always buy more bacon
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