Message-ID: <5A03089B.6060600@posteo.de>
Date: Wed, 08 Nov 2017 14:37:31 +0100
From: DK7FC <selberdenken@posteo.de>
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To: rsgb_lf_group@blacksheep.org
References: <22d6c712-43af-3a5d-099e-adb285f086a1@n1bug.com> <7d1279b6d1a84b692d281d48901f2b23@xs4all.nl> <a6d30d5a-dbb9-de7c-bb78-23e76a77fc58@n1bug.com>
In-Reply-To: <a6d30d5a-dbb9-de7c-bb78-23e76a77fc58@n1bug.com>
Subject: Re: LF: PA problem
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Hi Paul,

My answer may be a bit late.

It sounds to me like a EMC issue. A RF choke is needed in the supply 
line. 1 mH may be a good choice. And i would add a 1000 uF electrolytic 
capacitor with a low internal resistance (the good ones :-) ) near the 
Drain, in parallel to the 1 uF capacitor.

A few more arguments: It is not ideal to drive a class E with a linear 
signal. It is better (regarding efficiency) to use a hard keying by 
using a MOSFET driver such as ICL7667, TC4422 or so. A class E is not a 
design for linear modes, it is for a constant output power, good for 
QRSS/DFCW, CW, WSPR, OPERA, EbNaut...

I would recommend to build a class D PA. You can use the existing 
components. A class D is much less critical regarding matching (SWR) and 
the efficiency can be in a range of > 90% at LF as well...

73, Stefan


Am 08.11.2017 14:00, schrieb N1BUG:
> There were many replies to my plea for help. I won't reply to all 
> individually but every reply is much appreciated! Thank you all!
>
> To respond to a few things:
>
> I do not need a linear amp. I spent much time looking for a medium 
> power (50W or so) class E amp but could not find any designs. There 
> are many 250W and up class D circuits around but they all get out of 
> my budget for this year. I found this and since it was affordable I 
> decided to give it a try. I knew it was risky but better to try 
> something than do nothing at all.
>
> Capacitors in the LPFs are all WIMA FKP. I did not feel any heating. 
> Capacitors in the amp are also FKP.
>
> I'm afraid I have very little experience or confidence in working with 
> SSPAs of any type. I have designed and built many a tube PA up to 
> 1500W at HF through UHF but working with FETs is all new to me.
>
> I have to spend today working on a tower but will return to this 
> project and try some of the suggestions I received as soon as possible.
>
> 73,
> Paul N1BUG
>