VHF (and a little HF) PA impedance matching

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Re: VHF (and a little HF) PA impedance matching

Post by vk2aav on Thu Aug 01, 2013 3:02 am

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

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Re: VHF (and a little HF) PA impedance matching

Post by Admin on Wed Jul 31, 2013 5:18 pm

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

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Re: VHF (and a little HF) PA impedance matching

Post by Ivan on Wed Jul 31, 2013 10:48 am

Very nice article, Harry !
MNI TNX
VBR from Ivan

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VHF (and a little HF) PA impedance matching

Post by Admin on Tue Jul 30, 2013 4:16 pm

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

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