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Re: LF: PA problem

To: [email protected]
Subject: Re: LF: PA problem
From: DK7FC <[email protected]>
Date: Wed, 08 Nov 2017 14:37:31 +0100
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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





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