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WXlXy6cBuaqD_Rntx.4cj7OT00UpiNNhlCklCzSuwa5VIUrjecbIAcS1Fy8qm_xaYz2x_t0YofVW gIRxRNM.wsw-- Received: from sonic.gate.mail.ne1.yahoo.com by sonic311.consmr.mail.bf2.yahoo.com with HTTP; Mon, 25 Feb 2019 09:02:21 +0000 Date: Mon, 25 Feb 2019 09:02:16 +0000 (UTC) From: To: rsgb_lf_group@blacksheep.org Message-ID: <812506.4685789.1551085336681@mail.yahoo.com> MIME-Version: 1.0 References: <812506.4685789.1551085336681.ref@mail.yahoo.com> X-Mailer: WebService/1.1.13123 aolwebmail Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:65.0) Gecko/20100101 Firefox/65.0 X-Spam-Score: 0.0 (/) 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: Try using a synchronous keying circuit, only uses a few ics and is reliable. I have used it on a modified Decca 5501 on 136 and a similar tx on 475 with no blown fets even to a short circuit, guard ci [...] Content analysis details: (0.0 points, 5.0 required) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at http://www.dnswl.org/, no trust [74.6.131.123 listed in list.dnswl.org] -0.0 RCVD_IN_MSPIKE_H2 RBL: Average reputation (+2) [74.6.131.123 listed in wl.mailspike.net] -0.0 SPF_PASS SPF: sender matches SPF record 0.0 FREEMAIL_FROM Sender email is commonly abused enduser mail provider (gw8glo[at]aol.co.uk) 0.0 HTML_MESSAGE BODY: HTML included in message X-Scan-Signature: 070d9ab39265047b7fb462cd62854f10 Subject: Re: LF: Re: Class D current spikes Content-Type: multipart/alternative; boundary="----=_Part_4685788_492961906.1551085336679" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: *** X-Spam-Status: No, hits=3.6 required=5.0 tests=FORGED_MUA_MOZILLA,HTML_20_30, HTML_FONTCOLOR_UNKNOWN,HTML_MESSAGE,NO_REAL_NAME 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 ------=_Part_4685788_492961906.1551085336679 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Try using a synchronous keying circuit, only uses a few ics and is reliable= . I have used it on a modified Decca 5501 on 136 and a similar tx on 475 wi= th no blown fets even to a short circuit, guard circuit used as in the decc= a design.73 Dave =20 =20 =20 -----Original Message----- From: Eric NO3M To: rsgb_lf_group Sent: Sun, 24 Feb 2019 18:07 Subject: Re: LF: Re: Class D current spikes Andy =20 This recommendation is all well and good, but seems applicable to only CW = where either the operator is manually keying or using computer controlled k= eying with a constant carrier input. =20 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.=C2=A0 The s= pikes would still be present and problematic.=20 =20 Other than Rik's suggestion of killing the lingering active high driver ou= tput, it seems that only using a supply control scheme (whether driver or F= ET drain supply) would require sampling the original RF input to detect the= end of the envelope and apply the key up (inactive) signal.=C2=A0 Prior to= reaching the driver subsystem, the input RF would need to be delayed by so= me amount. =20 73 Eric NO3M =20 =20 On 2/24/19 9:41 AM, Andy Talbot wrote: =20 =20 For on-off keying of a switch mode PA you really should be using supply li= ne control.=C2=A0 Switching the drive then trying to reduce rise /fall time= s for keyclick elimination by controlling drive amplitude(something that se= ems to be done in some designs) is really asking for trouble.=C2=A0 Even h= ard-switching drive gives its problems , as we see here repeatedly=20 Instead, why not a simple emitter follower in the positive supply, then y= ou can apply waveform shaping=C2=A0 to the base drive at low current, where= you've got full control.=C2=A0 =C2=A0Even a 20A supply could be controlled= this way with a suitably rated transistor.=C2=A0 Quite likely have to be a= Darlington.=C2=A0 =C2=A0There will be a slight fixed drop across it, say 1= V 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.=20 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 modu= le couldn't manage. =C2=A0 Andy www.g4jnt.com =20 =20 =20 =20 =20 ------=_Part_4685788_492961906.1551085336679 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: 7bit
Try using a synchronous keying circuit, only uses a few ics and is reliable. I have used it on a modified Decca 5501 on 136 and a similar tx on 475 with no blown fets even to a short circuit, guard circuit used as in the decca design.
73 Dave



-----Original Message-----
From: Eric NO3M <no3m@no3m.net>
To: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Sent: Sun, 24 Feb 2019 18:07
Subject: Re: LF: Re: Class D current spikes

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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