Return-Path: Received: from rly-me06.mx.aol.com (rly-me06.mail.aol.com [172.20.83.40]) by air-me04.mail.aol.com (v126.13) with ESMTP id MAILINME043-9c44b0d6097357; Wed, 25 Nov 2009 11:51:59 -0500 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by rly-me06.mx.aol.com (v125.7) with ESMTP id MAILRELAYINME068-9c44b0d6097357; Wed, 25 Nov 2009 11:51:37 -0500 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1NDL4N-0004tR-Nf for rs_out_1@blacksheep.org; Wed, 25 Nov 2009 16:50:19 +0000 Received: from [83.244.159.144] (helo=relay3.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1NDL4N-0004tI-66 for rsgb_lf_group@blacksheep.org; Wed, 25 Nov 2009 16:50:19 +0000 Received: from out1.ip01ir2.opaltelecom.net ([62.24.128.237]) by relay3.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1NDL4L-0004PL-27 for rsgb_lf_group@blacksheep.org; Wed, 25 Nov 2009 16:50:19 +0000 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: ApoEAEPvDEtcHcMt/2dsb2JhbADWLIQyBA X-IronPort-AV: E=Sophos;i="4.47,287,1257120000"; d="scan'208";a="122234229" Received: from unknown (HELO xphd97xgq27nyf) ([92.29.195.45]) by out1.ip01ir2.opaltelecom.net with SMTP; 25 Nov 2009 16:50:09 +0000 Message-ID: <001b01ca6def$57a0fca0$0401a8c0@xphd97xgq27nyf> From: "mal hamilton" To: References: <001901ca6de6$a34b30c0$0900a8c0@lark> Date: Wed, 25 Nov 2009 16:48:21 -0000 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2600.0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2600.0000 X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,none Subject: LF: Re: Re: instability on MosFet amps Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.0 required=5.0 tests=none autolearn=no version=2.63 X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false X-AOL-IP: 193.82.116.20 Alan and Co I am using a LPF consisting of 2 x T200 type material with no adverse effects and insertion loss virtually nil. It works well with my class E PA and 1/4 wave inv L antenna. de mal/g3kev ----- Original Message ----- From: "Alan Melia" To: Sent: Wednesday, November 25, 2009 3:45 PM Subject: LF: Re: instability on MosFet amps > Hi Wolf this may not be the case with the properly tuned Class-E stage which > has relatively low distortion. It does not output a square-wave as some > think. See The QST article by Nat Sokal. > > Bear in mind filters complicate things further since they can transform > mis-matches and only really work if resistively terminated. Even more reason > to get your antenna right first. Loaded diplexor filters are a little more > forgiving if you have harmonic problems but should not be necessary on > Class-E a simple low-pass half-wave filter works well but use air cored > coils, not toroids. > > Alan G3NYK > > ----- Original Message ----- > From: "Wolf Ostwald" > To: > Sent: Wednesday, November 25, 2009 3:25 PM > Subject: LF: instability on MosFet amps > > > > Hello group ! > > > > I found that almost all amp configurations generate harmonics. In case of > a > > homebrewed HF amp, with a push -pull design, I had to build hi-pass > filters > > with a resistive termination, so called split filters, for each band. > > Without dissipating the harmonic energy the stage will have to cope with > > excess voltages and thus bury the MosFets . > > > > My last amp stage for the DI2BJ-beacon is followed by a hi-pass that opens > > at 750 kcs . This way the first harmonic and all the higher ones go into > > thermal dissipation. > > > > A T-type adjustable low-pass is used to match and reduce harmonics > further. > > > > Have fun de wolf df2py > > > > > >