I don't follow the SWR thing at all, since I wouldn't expect it to be an issue at such small fractions of a wavelength. (but I'm no transmission line expert)
I can see how -40dB level of any harmonic well past 150kHz could a challenge. Audio amplifier of old (Class AB analogue with one that one fb loop) used to claim THD < 0.05% to at least 20kHz. So 1% THD out to 150kHz might not be unreachable, at least for those older amps. Slew rate limit might be a gotcha. _______________________________________________________________________________ Ralph McDiarmid | Schneider Electric | Solar Business | CANADA | Regulatory Compliance Engineering From: don_borow...@selinc.com To: EMC-PSTC@LISTSERV.IEEE.ORG Date: 01/25/2012 08:09 AM Subject: Re: [PSES] Power Amp for IEC 61000-4-16 Ken- I have not only one, but two amplifiers that start at 10 kHz: an AR 25A100 (25 watts) and an AR 150A100A (150 watts). I only need 15 Vrms (4.5 watts) into a 50 ohm load from the 50 source impedance of the amplifier, so what is the problem? Well, the standard also requires the that source impedance be between 45 and 55 ohms. That doesn't sound so bad until you translate that into SWR (1.1:1 and 1.11:1) and compare that to the 2:1 output impedance specification of the amplifiers. To get a good enough match, I need to add an attenuator to the output of the amplifier. Running the math, one finds that 9 dB of attenuation is needed. I do have a 10 dB high power attenuator. Of course, that means that the amplifier now needs to put out 45 watts to deliver the 4.5 watts into the 50 ohm load. The 25 watt amplifier is out of the running at this point. I was able to simply add a series resistor to (barely) get the output impedance into the 45 to 55 ohm range over 10 kHz to 150 kHz. This would minimize the amount of attenuation. But... That 1% THD spec doesn't seem that bad until one realizes this means that the harmonics need to be better than -40 dBc. Turns out that both amplifiers at their low frequency limits (10 kHz) have increased distortion, though still within their -20 dBc specifications. In fact, even the 150 watt amplifier cannot deliver 4.5 watts with -40 dBc harmonics at 10 kHz into 50 ohms (no attenuator at the output). Audio amps are just fine up to 20 kHz or so, but fall apart rapidly after that. If they can deliver 30 Vrms open circuit (amp rated at more than 112.5 watts into 8 ohms), their distortion goes up rapidly as the feedback loop gain drops at the high frequencies. So what started out seeming to be a fairly simply measurement problem that might require a bit of tweaking turns out to be quite a head-spinner. I blame the standard. The distortion requirement is well beyond what is needed to insure an accurate test signal level. It seems the standard is trying to prevent false failures caused by harmonics. In other standards such as IEC 61000-4-3 radiated immunity (-6 dBc harmonics in the RF field) and IEC 61000-4-6 conducted immunity (-15 dBc harmonics in the test signal), there are statements indicating that the harmonic levels may be high enough to cause false failures and the tester need to exercise care to make sure this is not the case. I personally had to suppress harmonics to -60 dBc in the GSM band when testing a GSM clock to IEC 61000-4-3 radiated immunity, 80-1000 MHz. It would be absurd to require -60 dBc harmonics as a general requirement for radiated immunity testing. Note: I have made my views known to at least one US member of the relevant IEC committee. Donald Borowski EMC Compliance Engineer Schweitzer Engineering Labs Pullman, WA, USA From: Ken Javor <ken.ja...@emccompliance.com> To: <EMC-PSTC@LISTSERV.IEEE.ORG> Date: 01/24/2012 08:33 PM Subject: Re: [PSES] Power Amp for IEC 61000-4-16 Sent by: emc-p...@ieee.org I?m not familiar with the 61000-4-16 standard and its limit. If the limit is flat and requires 30 Vrms oc output at 150 kHz, that would indeed be a problem if you had to do it with an audio amplifier, but of course that isn?t necessary. Every lab has a 50 Ohm output amplifier that starts at 10 kHz. So the audio amp need only have flat performance out to 10 kHz, and they will all do that. Ken Javor Phone: (256) 650-5261 From: <ralph.mcdiar...@schneider-electric.com> Date: Tue, 24 Jan 2012 17:06:27 -0800 To: <EMC-PSTC@LISTSERV.IEEE.ORG> Subject: Re: [PSES] Power Amp for IEC 61000-4-16 1% THD all the way to 150kHz? Just wondering if the older analogue amps could do that, not to mention the (Class D?) amplifiers of today. Why not just put a 50 ohm resistor in series with the amplifier output. Audio amps should have no trouble operating into an open circuit. A 100W/ch amp should satisfy the 30Vrms requirement, but the THD might be a problem at the highest frequencies. _______________________________________________________________________________ Ralph McDiarmid | Schneider Electric | Solar Business | CANADA | Regulatory Compliance Engineering From: Ken Javor <ken.ja...@emccompliance.com> To: EMC-PSTC@LISTSERV.IEEE.ORG Date: 01/24/2012 03:45 PM Subject: Re: [PSES] Power Amp for IEC 61000-4-16 Any decent quality audio power amplifier will have THD below 1% these days. Consider using a step-up transformer such as the Solar Electronics 8810-1. It is designed to impedance match from 1.5 Ohms to 50 Ohms, and can handle 200 Watts. That will more than suffice for your needs. Ken Javor Phone: (256) 650-5261 > From: <don_borow...@selinc.com> > Date: Tue, 24 Jan 2012 15:30:55 -0800 > To: <emc-p...@ieee.org> > Subject: Power Amp for IEC 61000-4-16 > > A new testing requirement for some of my company's products is IEC > 61000-4-16 Conducted Common Mode Disturbances. I need to test from 10 kHz > to 150 kHz. > > I have a good low distortion signal source, but I need a power amplifier > to give me the signal at the test level: 30 Vrms open circuit, 50±5 ohms > source impedance, total harmonic distortion below 1%. While this sounds > like something not far beyond the capability of a good audio amplifier > (with a series 50 ohm resistor at the output), it is proving rather > difficult to find such an amplifier. Amplifier Research and Techron both > have amplifiers that are close but not quite there (either voltage swing > or distortion). > > I can buy complete solutions from EM Test, Frankonia, EMC Partner, and HV > Technologies. But I believe that there must be a power amplifier out there > that can do the job. > > Ideas anyone? > > Donald Borowski > EMC Compliance Engineer > Schweitzer Engineering Labs > Pullman, WA, USA - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <emcp...@radiusnorth.net> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
