Return-Path: Received: from mtain-dh11.r1000.mx.aol.com (mtain-dh11.r1000.mx.aol.com [172.29.65.31]) by air-di04.mail.aol.com (v126.13) with ESMTP id MAILINDI042-eac34b71be2d2b1; Tue, 09 Feb 2010 14:57:33 -0500 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by mtain-dh11.r1000.mx.aol.com (Internet Inbound) with ESMTP id 0FCFC3800056A; Tue, 9 Feb 2010 14:57:30 -0500 (EST) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1NewBK-0004ot-HH for rs_out_1@blacksheep.org; Tue, 09 Feb 2010 19:55:34 +0000 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1NewBJ-0004ok-V8 for rsgb_lf_group@blacksheep.org; Tue, 09 Feb 2010 19:55:33 +0000 Received: from cavuit01.kulnet.kuleuven.be ([134.58.240.43]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1NewBF-0004AN-8A for rsgb_lf_group@blacksheep.org; Tue, 09 Feb 2010 19:55:33 +0000 Received: from smtps02.kuleuven.be (smtpshost02.kulnet.kuleuven.be [134.58.240.75]) by cavuit01.kulnet.kuleuven.be (Postfix) with ESMTP id 6FBFA7B804D for ; Tue, 9 Feb 2010 20:55:16 +0100 (CET) Received: from ICTS-S-HUB-N1.luna.kuleuven.be (icts-s-hub-n1.luna.kuleuven.be [10.112.9.11]) by smtps02.kuleuven.be (Postfix) with ESMTP id 7885FF3862 for ; Tue, 9 Feb 2010 20:55:16 +0100 (CET) Received: from ICTS-S-EXC2-CA.luna.kuleuven.be ([10.112.11.13]) by ICTS-S-HUB-N1.luna.kuleuven.be ([10.112.9.11]) with mapi; Tue, 9 Feb 2010 20:55:16 +0100 X-Kuleuven: This mail passed the K.U.Leuven mailcluster From: Rik Strobbe To: "rsgb_lf_group@blacksheep.org" Date: Tue, 9 Feb 2010 20:53:04 +0100 Thread-Topic: PA matching oddity Thread-Index: Acqpq3geGDY/MJO6SRq0dAwf78TjNAAFgZM7 Message-ID: References: In-Reply-To: Accept-Language: nl-NL, nl-BE Content-Language: nl-BE X-MS-Has-Attach: X-MS-TNEF-Correlator: acceptlanguage: nl-NL, nl-BE MIME-Version: 1.0 X-KULeuven-Information: Katholieke Universiteit Leuven X-KULeuven-Scanned: Found to be clean X-KULeuven-Envelope-From: rik.strobbe@fys.kuleuven.be X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001 Subject: LF: RE: PA matching oddity Content-Type: multipart/alternative; boundary="_000_BF4A524700075746A6467658DFC7102C1284D4B33EICTSSEXC2CAlu_" 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, TO_ADDRESS_EQ_REAL 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-global-disposition: G x-aol-sid: 3039ac1d411f4b71be2a027d X-AOL-IP: 193.82.116.20 X-Mailer: Unknown (No Version) --_000_BF4A524700075746A6467658DFC7102C1284D4B33EICTSSEXC2CAlu_ Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Andy, have a look here : http://www.polyfet.com/HFE0503_Leong.pdf http://www.semelab.com/rf/documents/Push-Pull%20Circuits%20and%20Wideband%= 20Transformers.pdf 73, Rik ON7YD - OR7T ________________________________ Van: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.or= g] namens Andy Talbot [andy.g4jnt@googlemail.com] Verzonden: dinsdag 9 februari 2010 18:10 Aan: rsgb_lf_group@blacksheep.org; ukmicrowaves@yahoogroups.com Onderwerp: LF: PA matching oddity Has anyone got practical experience of the output matching transformers us= ed on MOSFET PAs - I've got a confusing one here? I recently acquired some big HF PA modules, each rated at over 1kW out, an= d made up from 8 MOSFETS, RFPP53 types, roughly equivalent to MRF140. It= runs from what is more than likely a 50V rail. The modules were part of= an industrial RF heater running at 13.56MHz, but the design is wideband(i= sh) with the normal ferrite matching transformers at input and output. Wh= ich is where I may be missing something - they may not be quite so normal.= .. The output transformer has a slightly different topology to designs seen= before - such as those given in the Motorola handbook. The secondary win= ding is made of insulated coax, two turns are full screened as they pass= through the cores / tubing, but each turn has the braid cut at the hot en= d and joined to the two ends of the secondary, with the third turn consist= ing just the inner conductor with no braid over it. All three turns (tw= o of coax plus the single core) sit inside the usual single turn primary= made up from brass tube, surrounded by a pair of ferrite cores with a con= nection at the far end. A diagram can be seen at http://www.g4jnt.com/p= amatch.gif Now, the bit that doesn't seem right... the impedances don't work out properly... Assuming it is designed to run into 50 ohms, a 1:3 transformer will presen= t a load of 5.56 ohms to the push pull devices. From a 50V rail this sh= ould result in a maximum power output of 2*(50^2)/5.56 =3D 900 Watts. = (Sanity check, a single ended design at half the Rload =3D (50^2)/ 2= / 2.78 =3D 450 Watts each- normal push pull PA calculation). Which is= not 1kW and is only an absolute theoretical maximum, anyway. BUT, if the transformer were 1:4 instead, , Rload would be 3.125 ohms,= Pout max would be 1600 watts which is exactly the sort of value I'd expec= t to see on a real 1kW rated PA module. Has anyone met that winding configuration before? Is it really the 1:3= turns ratio it intuitively looks like, or is there some way the windings= could have have become an auto-transformer and be giving 1:4 turns ratio= ? If it really is 1:3 will have to assume the voltage supply may be higher.= But for a 10 year old design, sounds very unlikely. A few pictures of the O/P transformer: http://www.g4jnt.com/PAtfmr1.jpg= http://www.g4jnt.com/PAtfmr2.jpg http://www.g4jnt.com/PAtfmr3.jpg On a quick test on the module today, running from a 10A supply, it delive= red nearly 150 Watts with the PSU current limiting and dragging the supply= volts down to 17V. Now, plugging these values into the matching equation= 2 * (17^2) / 5.556 =3D 100 Watts max possible, - but I was seeing more= power. ........ Extra support to the possibility of it being 1:4 - BUT HOW ? Andy www.g4jnt.com --_000_BF4A524700075746A6467658DFC7102C1284D4B33EICTSSEXC2CAlu_ Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Andy,<= /font>
 
have a look here :
 
 
73, Rik  ON7YD - OR= 7T
 
Van: owner-rsgb_lf_group@blackshee= p.org [owner-rsgb_lf_group@blacksheep.org] namens Andy Talbot [andy.g4jnt@= googlemail.com]
Verzonden: dinsdag 9 februari 2010 18:10
Aan: rsgb_lf_group@blacksheep.org; ukmicrowaves@yahoogroups.com
Onderwerp: LF: PA matching oddity

Has anyone got practical experience of the output matching transforme= rs used on MOSFET PAs - I've got a confusing one here?
 
I recently acquired some big HF PA modules, each rated at over= 1kW out, and made up from 8 MOSFETS,  RFPP53 types, roughly equivale= nt to MRF140.  It runs from what is more than likely a 50V rail. = ; The modules were part of an industrial RF heater running at 13.56MHz, but the design is wideband(ish) with the norm= al ferrite matching transformers at input and output.  Which is where= I may be missing something - they may not be quite so normal...
 
The output transformer has a slightly different topology to designs= seen before - such as those given in the Motorola handbook.  Th= e secondary winding is made of insulated coax, two turns are full screened= as they pass through the cores / tubing, but each turn has the braid cut at the hot end and joined to the two ends of= the secondary, with the third turn consisting just the inner conduct= or with no braid over it.    All three turns (two of coax= plus the single core) sit inside the usual single turn primary made up from brass tube, surrounded by a pair of ferrite cores with a con= nection at the far end.    A diagram can be seen at http://www.= g4jnt.com/pamatch.gif  
 
Now, the bit that doesn't seem right...
the impedances don't work out properly...
 
Assuming it is designed to run into 50 ohms, a 1:3 transformer will= present a load of 5.56 ohms to the push pull devices.   = From a 50V rail this should result in a maximum power output of 2*(50^2)/= 5.56 =3D 900 Watts.    (Sanity check,  a single ended= design at half the Rload =3D   (50^2)/ 2 / 2.78 =3D 450 Watts each- no= rmal push pull PA calculation).   Which is not 1kW and is only= an absolute theoretical maximum, anyway.
 
BUT,   if the transformer were 1:4 instead, , Rload would= be 3.125 ohms, Pout max would be 1600 watts which is exactly the sort of= value I'd expect to see on a real 1kW rated PA module.
 
Has anyone met that winding configuration  before?  = Is it really the 1:3 turns ratio it intuitively looks like, or is there= some way the windings could have have become an auto-transformer and = ;be giving  1:4 turns ratio ?
If it really is 1:3 will have to assume the voltage supply may be hig= her.  But for a 10 year old design, sounds very unlikely. 
 
 
On a quick test on the module today, running from a  10A su= pply, it delivered nearly 150 Watts with the PSU current limiting and drag= ging the supply volts down to 17V.  Now, plugging these values into= the matching equation 2 * (17^2) / 5.556 =3D 100 Watts max possible,  - but I was seeing more power.   =
 ........ Extra support to the possibility of it being 1:4 - BUT= HOW ?
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