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Re: LF: VO1NA_OK2BVG

To: [email protected]
Subject: Re: LF: VO1NA_OK2BVG
From: Stefan Schäfer <[email protected]>
Date: Fri, 28 Mar 2014 11:09:11 +0100
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Hi Joe,

Class E is fascinating and can be high efficient, 98% or so. However the output impedance has to be quite exactly 50 Ohm +-j0! A SWR of 1.5 can reduce the efficiency significantly so that all the advantages of the class E design are lost. Thus, i'm using class-D designs. I have 2 PAs for 630m. A small one running at 12 VDC, https://dl.dropboxusercontent.com/u/19882028/MF/100W-475KHZ-PA.png and https://dl.dropboxusercontent.com/u/19882028/MF/DK7FC%20472%20kHz%20PA%2015W%2B100W.JPG and a large one giving 0...1.2 kW, running as a H bridge, switching directly at 320V DC.
The efficiency can easily reach more than 90% too.
For you, i assume a normal class D using 2 (or 2x2) FETs against ground, using a ferrite output transformer may be the best choice. This design is used by many active MF stns, i know.
What power range do you inted to realise?

73, Stefan/DK7FC

Am 28.03.2014 00:24, schrieb [email protected]:
Hi Stefan,

I have some IRFP140BPF hexfets. Using Alan's G3NYK Class E
design spreadsheet for 200 watts at 13.8 Vdd gives 144 and 119 nf
for C1 and C2 and 1.14 uH for L.  I have used silver mica for C1 and C2
but these are expensive. What do you use? I remember mentioned your class e experiments.

73
Joe

On Wed, 26 Mar 2014, Stefan Schäfer wrote:


Am 26.03.2014 19:36, schrieb [email protected]:
Perhaps some day I will QRO!

Joe

Yes, please :-)

73, Stefan




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