Return-Path: Received: from rly-db02.mx.aol.com (rly-db02.mail.aol.com [172.19.130.77]) by air-db04.mail.aol.com (v126.13) with ESMTP id MAILINDB043-aaf4b27a2fd34c; Tue, 15 Dec 2009 09:55:03 -0500 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by rly-db02.mx.aol.com (v125.7) with ESMTP id MAILRELAYINDB025-aaf4b27a2fd34c; Tue, 15 Dec 2009 09:53:54 -0500 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1NKYiT-0005ji-Cv for rs_out_1@blacksheep.org; Tue, 15 Dec 2009 14:49:33 +0000 Received: from [83.244.159.144] (helo=relay3.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1NKYiS-0005jZ-6u for rsgb_lf_group@blacksheep.org; Tue, 15 Dec 2009 14:49:32 +0000 Received: from lnx503.hrz.tu-darmstadt.de ([130.83.156.232]) by relay3.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1NKYk7-0004Jd-Vd for rsgb_lf_group@blacksheep.org; Tue, 15 Dec 2009 14:51:18 +0000 Received: from FILE-SERVER-HST.hst.e-technik.tu-darmstadt.de (File-Server-HST.hst.e-technik.tu-darmstadt.de [130.83.212.129]) by lnx503.hrz.tu-darmstadt.de (8.14.2/8.14.2/HRZ/PMX) with SMTP id nBFEpEiM014033 for ; Tue, 15 Dec 2009 15:51:15 +0100 (envelope-from schaefer@hst.tu-darmstadt.de) Received: from [127.0.0.1] (helo=File-Server-HST.hst.e-technik.tu-darmstadt.de) by FILE-SERVER-HST.hst.e-technik.tu-darmstadt.de with AVK MailGateway; for ; Tue, 15 Dec 2009 15:51:14 +0100 Content-class: urn:content-classes:message MIME-Version: 1.0 X-MimeOLE: Produced By Microsoft Exchange V6.5 Date: Tue, 15 Dec 2009 15:51:16 +0100 Message-ID: <38A51B74B884D74083D7950AD0DD85E828AC7C@File-Server-HST.hst.e-technik.tu-darmstadt.de> In-Reply-To: X-MS-Has-Attach: X-MS-TNEF-Correlator: Thread-Topic: Re: "Gain" between qrss3 and qrss10 / PA design Thread-Index: Acp9kZshlaMyUSMRRv+U1PL4qaQAhgAAUtsw From: =?iso-8859-1?Q?Stefan_Sch=E4fer?= To: X-AVK-Virus-Check: AVB 19.625;15.12.2009 X-PMX-TU: seen v0.99a by 5.5.8.383112, Antispam-Engine: 2.7.2.376379, Antispam-Data: 2009.12.15.144216 X-PMX-SPAMCHECK: outgoing mail X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001 Content-Type: multipart/alternative; boundary="----_=_NextPart_001_01CA7D96.0CC88541" Subject: LF: AW: Re: "Gain" between qrss3 and qrss10 / PA design X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.2 required=5.0 tests=HTML_50_60,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 X-AOL-IP: 193.82.116.20 X-Mailer: Unknown (No Version) ------_=_NextPart_001_01CA7D96.0CC88541 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Hello Jim! First i want to say that i am glad to meet you here. Do you remember our= QSO in 2004? And mni tnx for your article to the tuning meter (and others= )! I have built it 2003 and it is for me the most useful measuring device= on LF at all! Yes, on 137kHz a half bridge is also a good idea since the losses are quit= e small. But, for a half or full bridge like in these decca transmitters,= one needs an output ferrite core that can handle the whole output power.= I think these are expensive (?), not easy to get and could be driven into= saturation when dimensioned well. In my class e PA I use a single (!) IRF= P360 that costs 1,9 Euro in the moment. This PA can easily handle 1kW with= an efficiency of more than 96%. In the whole PA circuit, no ferrite cores= are used, just two iron powder cores for the output filter. The driver is= one cheap ICL7667, available for 1,1 Euro. All Capacitors are of the type= wima FKP1 (2kV version), costs are belo= w 1 Euro. So, I think a half bridge is more expensive? Best 73 and hope for another QSO!!! =20 Stefan / DK7FC =20 =20 -----Urspr=FCngliche Nachricht----- Von: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacks= heep.org] Im Auftrag von James Moritz Gesendet: Dienstag, 15. Dezember 2009 15:15 An: rsgb_lf_group@blacksheep.org Betreff: LF: Re: "Gain" between qrss3 and qrss10 / PA design =20 Dear Stefan, LF Group, =20 A much better choice of circuit topology for QRO transmitters using an=20 off-line rectified mains PSU of about 330V is the half- or full bridge,=20 voltage-mode class D, as used in the "Decca" PAs, and G4JNT's off-line=20 design. Here the peak voltage across each MOSFET is only equal to the DC= =20 supply voltage, so cheap 500V Mosfets designed for off-line SMPSUs are=20 ideal. The class E and push-pull current-mode class D designs are better= for=20 relatively low voltage supplies, say < 40V. =20 The limitation on TX power that can be used at LF with a vertical antenna= is=20 the antenna voltage, roughly Iant * XCant. In my experience, corona=20 breakdown becomes a problem in the 10 - 20kV range with a wire antenna. So= =20 to use high power, and so achieve high antenna current and ERP, you need= =20 high antenna capacitance. Also, the voltage will be increased if the anten= na=20 loss resistance is low. I found that, with an 10m high inverted L antenna= of=20 about 50m of wire in total, I could run 1.2kW reliably, provided care was= =20 taken to eliminate sharp ends, narrow spacings, etc. in the antenna and=20 tuner. This resulted in up to 5A antenna current, and about 17kV on the=20 antenna wire. Even so, I have to increase the antenna height in order to= =20 approach 1W ERP. At 500k, the antenna impedance is much lower, and=20 efficiency also usually higher, so TX power is less of a problem. =20 In my experience, DX contacts using QRSS30 are quite practical, given a=20 large supply of strong coffee! But with longer dot periods, good propagati= on=20 does not last long enough to complete even a minimal QSO. =20 Cheers, Jim Moritz 73 de M0BMU =20 =20 ------_=_NextPart_001_01CA7D96.0CC88541 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable

Hello Jim!

First i want to say that i am glad to meet you here. Do you remember our QSO in= 2004? And mni tnx for your article to the tuning meter (and others)! I have buil= t it 2003 and it is for me the most useful measuring device on LF at all!

Yes, on 137kHz a half bridge is also a good idea since the losses are quite sma= ll. But, for a half or full bridge like in these decca transmitters, one needs an= output ferrite core that can handle the whole output power. I think these are expensive (?), not easy to get and could be driven into saturation when di= mensioned well. In my class e PA I use a single (!) IRFP360 that costs 1,9 Euro in= the moment. This PA can easily handle 1kW with an efficiency of more than 96%.= In the whole PA circuit, no ferrite cores are used, just two iron powder core= s for the output filter. The driver is one cheap ICL7667, available for 1,1 Euro= . All Capacitors are of the type wima= FKP1 (2kV version), costs are below 1 Euro. So, I think a half bridge is more expensive?

Best 73 and hope for another QSO!!!

 

Stefan / DK7FC

 

 

-----Urspr=FCngliche Nachricht-----
Von: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacks= heep.org] Im Auftrag von James Moritz
Gesendet: Dienstag, 15. Dezember 2009 15:15
An: rsgb_lf_group@blacksheep.org
Betreff: LF: Re: "Gain" between qrss3 and qrss10 / PA design

 

Dear Stefan, LF Group,=

 

A much better choice of circuit topo= logy for QRO transmitters using an

off-line rectified mains PSU of abou= t 330V is the half- or full bridge,

voltage-mode class D, as used in the= "Decca" PAs, and G4JNT's off-line

design. Here the peak voltage across= each MOSFET is only equal to the DC

supply voltage, so cheap 500V Mosfet= s designed for off-line SMPSUs are

ideal. The class E and push-pull cur= rent-mode class D designs are better for

relatively low voltage supplies, say= < 40V.

 

The limitation on TX power that can= be used at LF with a vertical antenna is

the antenna voltage, roughly Iant *= XCant. In my experience, corona

breakdown becomes a problem in the= 10 - 20kV range with a wire antenna. So

to use high power, and so achieve hi= gh antenna current and ERP, you need

high antenna capacitance. Also, the= voltage will be increased if the antenna

loss resistance is low. I found that= , with an 10m high inverted L antenna of

about 50m of wire in total, I could= run 1.2kW reliably, provided care was

taken to eliminate sharp ends, narro= w spacings, etc. in the antenna and

tuner. This resulted in up to 5A ant= enna current, and about 17kV on the

antenna wire. Even so, I have to inc= rease the antenna height in order to

approach 1W ERP. At 500k, the antenn= a impedance is much lower, and

efficiency also usually higher, so= TX power is less of a problem.

 

In my experience, DX contacts using= QRSS30 are quite practical, given a

large supply of strong coffee! But= with longer dot periods, good propagation

does not last long enough to complet= e even a minimal QSO.

 

Cheers, Jim Moritz

73 de M0BMU

 

 

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