Re: LF: Class E pa

[Rik Strobbe <rik.strobbe@fys.kuleuven.be>]

Hello Tony,

> I'm still using a Derivative of
> the Design from G3YXM's class E 1KW TX on LF

If you refer to the TX in

http://www.wireless.org.uk/136rig.htm : this is a class D TX, not
class E.
I am also using a "G3XYM clone" on 500kHz (with a pair of
IRFP350's). Running on 44V / 7 A it delivers just over 250W, about 82%
efficiency. It seems very forgiving to mismatch, no FET failures so far
(fingers crossed). But for testing purposes (antenna tuning) I run it on
13.6V (abt. 25W output) where it can handle any mismatch.

73, Rik  ON7YD

At 12:47 25/11/2009, you wrote:

Hi Mal
I'm still using a Derivative of the Design from G3YXM's class E 1KW TX on LF. Recently I've built a TX for 500 kHz using the same principle. It works great and delivers up to 500W. Unfortunately only into a dummy load, because 500 kHz is still not allowed here in Switzerland. But at least - I will be ready ;-)
73 de Toni, HB9ASB

2009/11/25 mal hamilton <g3kevmal@talktalk.net >

Ref recent discussion on the subject.

 

I use a class E pa on 500 kcs and never get any trouble.

As a general guide use high voltage fets and the fet V should be rated at  about 5 times the supply V and current about 3 times.

You arrive at class E by careful design not by accident.

Having designed and built the PA for the required power and load R usually 50 ohms adjust into a DL for correct waveform as displayed on a 'scope, this is important otherwise V spikes and instability will kill the fet.

Install a suitable antenna and match it with a suitable atu to 50 ohms so when you connect the TX/PA to the antenna they both match.

Check the wave form again and any slight mismatch should be adjusted by the antenna atu and NOT the pa.

The load does not have to be 50 ohms but this is convenient when testing with available test gear.

High V fets give more realistic C and Inductor and R values. A good range for fets is a psu giving 40 - 100 volts ie fets 500volts and a suitable current rating depending on your power. requirements ie if you need to draw 5 amps the fet should be rated 15 amps.

These are the general guidelines and work well for me.

Most amateurs seem to use class D amps whereas class E are rare.

 

de Mal/G3KEV