Return-Path: Received: from mtain-dd07.r1000.mx.aol.com (mtain-dd07.r1000.mx.aol.com [172.29.64.147]) by air-me06.mail.aol.com (v129.4) with ESMTP id MAILINME061-8bb44d30322431b; Fri, 14 Jan 2011 06:23:16 -0500 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-dd07.r1000.mx.aol.com (Internet Inbound) with ESMTP id D7D37380003CD; Fri, 14 Jan 2011 06:23:14 -0500 (EST) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1PdhjX-0005DL-6x for rs_out_1@blacksheep.org; Fri, 14 Jan 2011 11:22:19 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1PdhjW-0005DC-8j for rsgb_lf_group@blacksheep.org; Fri, 14 Jan 2011 11:22:18 +0000 Received: from mail-iy0-f171.google.com ([209.85.210.171]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1PdhjT-0006Mi-6b for rsgb_lf_group@blacksheep.org; Fri, 14 Jan 2011 11:22:18 +0000 Received: by iyj21 with SMTP id 21so2570114iyj.16 for ; Fri, 14 Jan 2011 03:22:08 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:in-reply-to:references:date :message-id:subject:from:to:content-type; bh=q17ePeLAcnENJZFrLwhtLI/mjcgeOey/9vEtwGETc64=; b=WHMWmuqVz05xpsm5WG+IPzqKbIRAbLNMkA2YaLhyL5f0DonsYHS5RhPLewQ50u+FOQ SCdDvzOX5Og/4SLupGkMOE/b5WNjHX+gz0NkTVzYUP9t6Gm+0hmTzBmb7EzhgfCLls29 wRJvolhjlJlfFkj/Tw0w3IHl+5bqLV2qDaCzw= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; b=h+hlXCb9GigFW7KYymNlzwVwF6TYi4q3hC6j4ZXm5ddzLWM1UxxNBbHFqRqCuePJR/ BxJ9JjsUh9nkrhAAaod9D2pe2oicQtuwKuGKGMO347qSvlzV2gCXqDZ1Ug0fEFQ712NJ 4QAeCYRFPEePQ8DoYDQ/sv9rS1gLHDv3vsuxg= MIME-Version: 1.0 Received: by 10.231.15.133 with SMTP id k5mr534869iba.187.1295004128270; Fri, 14 Jan 2011 03:22:08 -0800 (PST) Received: by 10.231.200.211 with HTTP; Fri, 14 Jan 2011 03:22:08 -0800 (PST) In-Reply-To: <002d01cbb3d3$ded8e9a0$0401a8c0@xphd97xgq27nyf> References: <003801cbb33e$8b59e620$0401a8c0@xphd97xgq27nyf> <004001cbb349$8b4ec190$0401a8c0@xphd97xgq27nyf> <4D2F705F.7020804@iup.uni-heidelberg.de> <002d01cbb3d3$ded8e9a0$0401a8c0@xphd97xgq27nyf> Date: Fri, 14 Jan 2011 11:22:08 +0000 Message-ID: From: Andy Talbot To: rsgb_lf_group@blacksheep.org DomainKey-Status: good (testing) X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001 Subject: Re: LF: Re: Re: FET RDS Content-Type: multipart/alternative; boundary=00032555f11a0c5a2c0499cca5da 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=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-global-disposition: G X-AOL-SCOLL-AUTHENTICATION: mail_rly_antispam_dkim-m201.2 ; domain : gmail.com DKIM : pass x-aol-sid: 3039ac1d40934d30322237db X-AOL-IP: 195.171.43.25 X-Mailer: Unknown (No Version) --00032555f11a0c5a2c0499cca5da Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Accurate LF Power measurement; Its all about calibration, accuracy, attention to detail, and thinking abo= ut the sources of all errors. If you think carefully about how to make measurements, even using amateur grade equipment you should be able to achieve decent accuracy. This is do= ne by making most of the errors cancel out so you only have to rely on equipment that can be trusted, or verified elswhere Here's how I make RF power measurements at LF/MF *Test equipment available:* DVM ; checked and compared with others and against IC voltage standard: Known accuracy < 0.2% Clamp Ammeter - accuracy 1% - by checking against 2 other DMMs on current range ,but prone to a few tens of mA offset drift. But when measuring in the several-amp region this is within the 2% Analogue 300MHz dual beam scope - which I regard as uncalibrated in absolu= te terms. However, it is linear over its full trace height , the attenuator volts/div is *relatively *accurat*e* to 1% over the range 0.01 - 5V/div an= d the response is flat from DC to frequency of interest. All that has been checked out in the past Linearity and frequency response are all that matters Bird 30dB 1kW attenuator, DC - 1GHz and 20dB coax attenuator (18GHz). 0- 50V DC variable PSU *Calibration Procedure:* Measure DC input resistance of Bird attenuator Set scope for 50 ohm term input, fed from the 50dB of combined attenuators Use DVM to set PSU to 50.0V DC output.and connect it to the input of the attenuator. View scope trace of the resulting DC level. It should be "about" 0.158V, which corresponds to 50 Watts in and 50dB of attenuation Adjust the scope "cal" control so the trace shows 1.58, or 3.16, or whatever, divisions. (In actual fact the attenuation of the Bird is 29.54dB at DC, total 49.62d= B - but that no longer matters - the scope trace is not calibrated) I now know the scope, which has a known decent front panel attenuator is calibrated and errors in RF power attenuator and scope and are cancelled out. The DC resistance of the Bird is 50.4 ohms - so only a potential 1% error there. That wouldn't have been taken out using the DC supply as reference So I can now read voltage on the scope to an accuracy of about 2 - 3% - an= d know its correct. *PA Measurement* Apply RF from PA to attenuator input, viewing output sinewave the screen. Pout =3D (Vpk-pk)^2 / 400 * 100000. Or a quick calculator Vp-p squared * 250 Don't need to asy much about the other half of the efficiency measurement. Even if the DVM weren't particulalrly accurate, the fact it= s the same as used for the DC voltage cal on the attenuator means any error cancels out. So now the *absolute* sources of error are : DVM calibration on one range - < 0.2% DC Current clamp ammeter - 2%, Scope readout resolution about 2% ish - depends if I squint hard enough! Load resistance 1% A perfectionist (or a contract-manager in my working days) would want erro= rs added - so 6% or so potential uncertainty A realist (or a contractor " " " " ) would use RSS addition of errors - so 3% realistic uncertainty Which still - even after all this attention to detail, means a measured 90= % efficiency could be 87 or 93% My value of 80% was actually the lower limit of errors, so actual value could be in the region of 80 - 86% Looking at the voltage across the FETs when on, especially at max Vdd, I= can see wher eall teh loss is going - although the tank coil does run a bit warmer than I'd have hoped for. Its wound with 2mm Litz, and really need= s thicker wire. As an alternative - a 50 ohm resistor and schottky diode + decoupling C into a Hi-Z DVM make a good power detector for RF in the few watts region= - like at the 30dB Bird output. PROVIDED it behaves as a peak hold detector, ie the decoupling cap does its job. A DC calibration is reasonably good for checking its ability to measure Vpeak (not pk-pk). = The reading is no longer linear, but does lend itself to lookup tables, and an absoute cal against the DVM knowing the diode drop is mostly constant-i= sh Whew.............! Andy www.g4jnt.com On 14 January 2011 10:14, mal hamilton wrote: > Stefan > At this sort of measured efficiency you would need very accurate calibra= ted > measuring equipment. > Figures of 96% are only possible with MAGIC FETS, RDS 0.0 and PA coils= with > wire resistance of 0 > Measure DC input V*I (watts) on load, then RF output into a dummy load= I > squared R (watts) subtract one result from the other ie loss and calcula= te > % > efficiency. > Instrument accuracy could be out of calibration by several percent. > 73 de mal/g3kev > > ----- Original Message ----- > From: "Stefan Sch=E4fer" > To: > Sent: Thursday, January 13, 2011 9:36 PM > Subject: Re: LF: Re: Re: FET RDS > > > > My LF 1 kW class E PA i using a single IRFP360 at > 96 % efficiency (a= t > > Z=3DR=3D50 Ohm of course). The driver is a ICL7667. The supply voltage= is 80 > > VDC. That's not a dream ;-) > > > > Stefan/DK7FC > > > > Am 13.01.2011 18:44, schrieb mal hamilton: > > > Jim > > > What you say is correct but it is virtually impossible to achieve th= e > 90% > > > plus efficiency claimed by some. The FET required in practice is not > > > available and these high efficiencies are only theoritical. > > > I have found this in practice ie 80% if you are lucky on a good day > > > mal/g3kev > > > > > > > > > ----- Original Message ----- > > > From: "James Moritz" > > > To: > > > Sent: Thursday, January 13, 2011 5:31 PM > > > Subject: LF: Re: FET RDS > > > > > > > > > > > >> Dear Mal, Andy, LF Group, > > >> > > >> There is a trade-off in construction of MOSFETs - basically, for a > given > > >> area of silicon, higher BVdss requires a thicker active region of= the > > >> MOSFET with higher on resistance. You can reduce Rdson by using a > greater > > >> chip area, but that means higher capacitances, increased cost, etc.= So > you > > >> can't have your cake and eat it. > > >> > > >> In Andy's breadboard circuit, there is a mismatch between the > available > > >> MOSFET type and the available PSU voltage - the 500V BVdss is a bit > too > > >> > > > high > > > > > >> for a 60V DC supply - the peak voltage in an ideal class E is 3.56= x > Vdc, > > >> perhaps you would allow 5 x Vdc for safety. 300V BVdss mosfets seem= a > bit > > >> thin on the ground, so more efficient schemes might be to increase= Vdc > to > > >> about 100V, or reduce it to about 40V and use lower Rdson 200V > mosfets. > > >> > > >> Cheers, Jim Moritz > > >> 73 de M0BMU > > >> > > >> > > >> > > >> > > > > > > > > --00032555f11a0c5a2c0499cca5da Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable
Accurate LF Power measurement;
Its all about calibration, accuracy, attention to detail, and thinkin= g about the sources of all errors.
=A0
If you think carefully about how to make measurements, even using ama= teur grade equipment you should be able to achieve decent accuracy.=A0 Thi= s is done by making most of the errors cancel out so you only have to rely= on equipment that can be trusted, or verified elswhere
Here's how I make RF power measurements at LF/MF
=A0
Test equipment available:
DVM ;=A0 checked and compared with others and against IC voltage stan= dard: Known accuracy < 0.2%
Clamp Ammeter - accuracy 1% - by checking against 2 other DMMs on=A0= current range ,but=A0 prone to a few tens of mA offset drift.=A0 But when= measuring in the=A0several-amp region this is within the 2%
=A0
Analogue 300MHz dual beam scope - which I regard as uncalibrated in= =A0absolute terms.=A0=A0However, it is linear over its full trace=A0height= =A0, the attenuator=A0 volts/div is relatively accurate to 1% over the range 0.01 - 5V/div and the response is fla= t from DC to frequency of interest.=A0 All that has been checked out in th= e past =A0 Linearity and frequency response are all that matters
=A0
Bird 30dB 1kW attenuator, DC - 1GHz =A0and 20dB coax attenuator (18GH= z).
0- 50V DC variable PSU
=A0
Calibration Procedure:
Measure DC input resistance of Bird attenuator
Set scope for 50 ohm term input, fed from the 50dB of combined attenu= ators
Use DVM to set PSU to 50.0V DC output.and connect it to the input of= the attenuator.
View scope trace of the resulting DC level.=A0 It should=A0be "a= bout" 0.158V, which corresponds to=A0 50 Watts in and 50dB of attenua= tion
Adjust the scope "cal" control so the trace shows 1.58, or= 3.16, or whatever, divisions.
(In actual fact the attenuation of the Bird is 29.54dB at DC, total= 49.62dB - but that no longer matters - the scope trace is not calibrated)=
=A0
I now know the scope, which has a known decent front panel attenuator= is calibrated and errors in RF power attenuator and scope and are cancell= ed out.=A0
The DC resistance of the=A0Bird is 50.4 ohms - so only a potential 1%= error there.=A0=A0That wouldn't have been taken out using the DC supp= ly as reference
=A0
So I can now read voltage on the scope to an accuracy of about 2 - 3%= - and know its correct.
=A0
PA Measurement
=A0
Apply RF from PA to attenuator input, viewing output sinewave=A0the= screen.=A0=A0 Pout =3D=A0 (Vpk-pk)^2 / 400 * 100000.=A0=A0
Or a quick calculator Vp-p squared * 250
=A0
Don't need to asy much about the other half of=A0 the efficiency= measurement.=A0=A0 Even if the DVM weren't particulalrly accurate, th= e fact its the same as used for the DC voltage cal=A0on the attenuator mea= ns=A0 any error cancels out.=A0=A0
=A0
So now the absolute sources of error are :
DVM calibration on one range=A0 - < 0.2%
DC Current clamp ammeter - 2%,
Scope readout resolution about 2% ish - depends if I squint hard enou= gh!
Load resistance 1%
=A0
A perfectionist (or a contract-manager in my working days) would want= errors added=A0 - so 6% or so potential uncertainty
A realist (or a contractor=A0=A0 "=A0=A0=A0=A0=A0=A0=A0 "= =A0=A0=A0=A0=A0=A0=A0 "=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 " )=A0= would use RSS addition of errors - so 3%=A0 realistic uncertainty
=A0
Which still - even after all this attention to detail, means a measur= ed 90% efficiency could be 87 or 93%
=A0
My value of 80% was actually the lower limit of errors, so actual val= ue could be in the region of 80 - 86%
Looking at the voltage across the FETs when on, especially at max Vdd= , I can see wher eall teh loss is going - although the tank coil does run= a bit warmer than I'd have hoped for.=A0=A0 Its wound with 2mm Litz,= and really needs thicker wire.
=A0
As an=A0alternative - a 50 ohm resistor and schottky diode + decoupli= ng C =A0into a Hi-Z DVM make a good power detector for RF in the few watts= region - like at the 30dB =A0Bird output.=A0=A0 PROVIDED it behaves as a= peak hold detector, ie=A0the decoupling cap does its job.=A0 =A0=A0A DC= calibration is reasonably good for checking its ability to measure Vpeak= (not pk-pk).=A0=A0 The reading is no longer linear, but does lend itself= to lookup tables, and an=A0absoute cal against the DVM knowing the diode= drop is mostly constant-ish
=A0
Whew.............!
=A0
Andy
=A0
=A0
=A0
=A0


On 14 January 2011 10:14, mal hamilton <g3kevmal@talktalk.n= et> wrote:
Stefan
At this sort of meas= ured efficiency you would need very accurate calibrated
measuring equip= ment.
Figures of 96% are only possible with MAGIC FETS, RDS 0.0 and PA coils wit= h
wire resistance of 0
Measure DC input V*I (watts) on load, then RF= output into a dummy load I
squared R (watts) subtract one result from= the other ie loss and calculate %
efficiency.
Instrument accuracy could be out of calibration by several= percent.
73 de mal/g3kev

----- Original Message -----
From:= "Stefan Sch=E4fer" <schaefer@iup.uni-heidelberg.de>
To: <rsgb_lf_group@blac= ksheep.org>
Sent: Thursday, January 13, 2011 9:36 PM
Subject:= Re: LF: Re: Re: FET RDS


> My LF 1 kW class E PA i using a= single IRFP360 at > 96 % efficiency (at
> Z=3DR=3D50 Ohm of course). The driver is a ICL7667. The supply voltag= e is 80
> VDC. That's not a dream ;-)
>
> Stefan/DK7= FC
>
> Am 13.01.2011 18:44, schrieb mal hamilton:
> >= Jim
> > What you say is correct but it is virtually impossible to achiev= e the
90%
> > plus efficiency claimed by some. The FET require= d in practice is not
> > available and these high efficiencies ar= e only theoritical.
> > I have found this in practice ie 80% if you are lucky on a good= day
> > mal/g3kev
> >
> >
> > -----= Original Message -----
> > From: "James Moritz"<james.moritz@btopenworld.com= >
> > To:<rsgb_lf_g= roup@blacksheep.org>
> > Sent: Thursday, January 13, 2011= 5:31 PM
> > Subject: LF: Re: FET RDS
> >
> > > >
> >> Dear Mal, Andy, LF Group,
> >>
&= gt; >> There is a trade-off in construction of MOSFETs - basically,= for a
given
> >> area of silicon, =A0higher BVdss requires= a thicker active region of the
> >> MOSFET with higher on resistance. You can reduce Rdson by us= ing a
greater
> >> chip area, but that means higher capacit= ances, increased cost, etc. So
you
> >> can't have your= cake and eat it.
> >>
> >> In Andy's breadboard circuit, there is= a mismatch between the available
> >> MOSFET type and the ava= ilable PSU voltage - the 500V BVdss is a bit too
> >>
>= > high
> >
> >> for a 60V DC supply - the peak voltage in an id= eal class E is 3.56 x
Vdc,
> >> perhaps you would allow 5= x Vdc for safety. 300V BVdss mosfets seem a
bit
> >> thin= on the ground, so more efficient schemes might be to increase Vdc
to
> >> about 100V, or reduce it to about 40V and use lower Rd= son 200V mosfets.
> >>
> >> Cheers, Jim Moritz
= > >> 73 de M0BMU
> >>
> >>
> >&g= t;
> >>
> >
>



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