Return-Path: Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by klubnl.pl (8.14.4/8.14.4/Debian-8+deb8u2) with ESMTP id x1OIAtjt018075 for ; Sun, 24 Feb 2019 19:11:02 +0100 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1gxy9I-0007i1-OL for rs_out_1@blacksheep.org; Sun, 24 Feb 2019 18:05:12 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1gxy97-0007hm-7s for rsgb_lf_group@blacksheep.org; Sun, 24 Feb 2019 18:05:01 +0000 Received: from 576e.8172.0000.0000.0210.4001.0d0f.7062.ip6.static.sl-reverse.com ([2607:f0d0:1004:120::2718:e675] helo=mx1.lylix.net) by relay1.thorcom.net with esmtp (Exim 4.91) (envelope-from ) id 1gxy95-0003nj-1t for rsgb_lf_group@blacksheep.org; Sun, 24 Feb 2019 18:05:00 +0000 Received: from no3m.local (dynamic-acs-24-144-206-160.zoominternet.net [24.144.206.160]) (Authenticated sender: eric@lylix.net) by mx1.lylix.net (Postfix) with ESMTPSA id 24F031A408BE for ; Sun, 24 Feb 2019 13:04:53 -0500 (EST) To: rsgb_lf_group@blacksheep.org References: <043bec62-8144-5ff3-98a6-9f04699f6a4c@no3m.net> <1551011916482.41235@kuleuven.be> <1551014480338.17397@kuleuven.be> <27248150-3565-aeb8-9b66-53a9089fd4ab@n1bug.com> <1551018171015.45843@kuleuven.be> From: Eric NO3M Message-ID: <81de6f2c-30cf-5142-fbd8-bd67416e97d7@no3m.net> Date: Sun, 24 Feb 2019 13:04:52 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.3.3 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-Spam-Score: 2.0 (++) X-Spam-Report: Spam detection software, running on the system "relay1.thorcom.net", has NOT identified this incoming email as spam. The original message has been attached to this so you can view it or label similar future email. If you have any questions, see the administrator of that system for details. Content preview: Andy This recommendation is all well and good, but seems applicable to only CW where either the operator is manually keying or using computer controlled keying with a constant carrier input. With digi modes (WSPR, JT9, etc.) that do not present a constant RF input, the traditional PTT signaling is of no use as it keys active prior to the RF envelope start and goes inactive after the RF en [...] Content analysis details: (2.0 points, 5.0 required) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 SPF_PASS SPF: sender matches SPF record 0.0 HTML_MESSAGE BODY: HTML included in message 2.0 KHOP_DYNAMIC Relay looks like a dynamic address X-Scan-Signature: 54f9a9b24d9d5f31a632377c3b90b222 Subject: Re: LF: Re: Class D current spikes Content-Type: multipart/alternative; boundary="------------FD2AB5AB36422392F9BEC655" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.5 required=5.0 tests=HTML_20_30,HTML_MESSAGE 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 This is a multi-part message in MIME format. --------------FD2AB5AB36422392F9BEC655 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Andy This recommendation is all well and good, but seems applicable to only CW where either the operator is manually keying or using computer controlled keying with a constant carrier input. With digi modes (WSPR, JT9, etc.) that do not present a constant RF input, the traditional PTT signaling is of no use as it keys active prior to the RF envelope start and goes inactive after the RF envelope ends.  The spikes would still be present and problematic. Other than Rik's suggestion of killing the lingering active high driver output, it seems that only using a supply control scheme (whether driver or FET drain supply) would require sampling the original RF input to detect the end of the envelope and apply the key up (inactive) signal.  Prior to reaching the driver subsystem, the input RF would need to be delayed by some amount. 73 Eric NO3M On 2/24/19 9:41 AM, Andy Talbot wrote: > For on-off keying of a switch mode PA you really should be using > supply line control.  Switching the drive then trying to reduce rise > /fall times for keyclick elimination by controlling drive > amplitude(something that seems to be done in some designs) is really > asking for trouble.  Even hard-switching drive gives its problems , as > we see here repeatedly > > Instead, why not a simple emitter follower in the positive supply, > then you can apply waveform shaping  to the base drive at low current, > where you've got full control.   Even a 20A supply could be controlled > this way with a suitably rated transistor.  Quite likely have to be a > Darlington.   There will be a slight fixed drop across it, say 1V at > saturation / full power, so a few watts of dissipation, but it's only > operating non saturated for a short period during the rise / fall times. > > A power FET could be used, but you'd need a drive voltage Vgs higher > than the supply, albeit only a few mA capability; nothing a small > switcher module couldn't manage. > > Andy > www.g4jnt.com > > > --------------FD2AB5AB36422392F9BEC655 Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: 8bit Andy

This recommendation is all well and good, but seems applicable to only CW where either the operator is manually keying or using computer controlled keying with a constant carrier input.

With digi modes (WSPR, JT9, etc.) that do not present a constant RF input, the traditional PTT signaling is of no use as it keys active prior to the RF envelope start and goes inactive after the RF envelope ends.  The spikes would still be present and problematic.

Other than Rik's suggestion of killing the lingering active high driver output, it seems that only using a supply control scheme (whether driver or FET drain supply) would require sampling the original RF input to detect the end of the envelope and apply the key up (inactive) signal.  Prior to reaching the driver subsystem, the input RF would need to be delayed by some amount.

73 Eric NO3M


On 2/24/19 9:41 AM, Andy Talbot wrote:
For on-off keying of a switch mode PA you really should be using supply line control.  Switching the drive then trying to reduce rise /fall times for keyclick elimination by controlling drive amplitude(something that seems to be done in some designs) is really asking for trouble.  Even hard-switching drive gives its problems , as we see here repeatedly

Instead, why not a simple emitter follower in the positive supply, then you can apply waveform shaping  to the base drive at low current, where you've got full control.   Even a 20A supply could be controlled this way with a suitably rated transistor.  Quite likely have to be a Darlington.   There will be a slight fixed drop across it, say 1V at saturation / full power, so a few watts of dissipation, but it's only operating non saturated for a short period during the rise / fall times.

A power FET could be used, but you'd need a drive voltage Vgs higher than the supply, albeit only a few mA capability; nothing a small switcher module couldn't manage.
 



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