Resources about HF power amplifier

[E-goe]

Hi

I need some documents about HF power Amplifier design.

My purpose:

The transmitter that we are currently using is a power amplifier( 1.6...30MHz) of 300W and is using traditional bipolair transistors in a class AB configuration.

Does somebody has any experience, knows some interresting docs or links that tells about how to "upgrade" using MOSFETS instead of bipolair transistors?

Also I want to parrallel some of this transmitter to design an even stronger transmitter ( about 5kW).

So what are the consequences, good or bad about this change I want to make, the difficulties of this change?

Greetz E-goe

 

[unkarc]

Re: HF Power amplifier

Hi E-goe,

Personally I have not built kW power amps but am familiar a little with this topic. One thing first: I have not seen any reference or description on changing/"upgrading" from bipolar power transistors to power FETs in an existing PA. It is possible someone did it but usually the design starts with FEts if a FET PA is needed.

Here are some links useful in your topic:
**broken link removed** this is actually a Motorola appication note, written by Helge Granberg, an authority on HF PAs, both bipolar and FET, (unfortunately he passed away a few years ago).

A good discussion on PAs with practical power devices + reference literature is here:
http://lists.contesting.com/archives/html/Amps/1998-01/msg00011.html
(Some of the referenced papers are also on the web if you search for them by their key title words with google.com; it is true that this discussion is dated back to January, 1998 but most of its points are still valid.)
See also
http://www.qsl.net/ab4oj/quadra/sshfamp.html and
http://www.qsl.net/ik4auy/article_4_english.htm and a collection of further links to some good application notes:
**broken link removed**

I hope these are of some help and maybe others here can supply further info to you.

rgds
unkarc

 

[toonafishy]

Re: HF Power amplifier

I have designed both bipolar and mosfet 300W modules. The main difference is the driving circuit. On a bipolar, you are trying to get power into the base of a transistor with a very low real impedance - not a trivial task. On the other hand, the mosfet input is mostly capacitive - again not trivial. The biasing cirucit is also different. So you cannot just swap out the transistors - circuits need to be designed.
I've also used coaxial cable wound around ferrite cores to split the drive to 4 modules and then another to combine the output. 4x300W modules for a total output of 1200W 1.6 to 30 MHz.
The best book on this subject is Radio Frrequency Taransistors by Norm Dye and Helge Granberg of Motorola fame. If you are serious about this stuff, find this book.

 

[flatulent]

Re: HF Power amplifier

This company **broken link removed** has the Motorola application notes on such amplifiers. They also have kits of parts including the PC card for making them. This will provide a first cut at your new design and you can do whatever modifications you want to the prototype you build from the kits.

 

[zerc]

Re: HF Power amplifier

if you want a power 5kw in am modulation you can use mosfet in class e and a pwm modulator. it is not so difficult and the result is great.search the internet for class e amplifier