At the low end the models are very, very good. Above 10MHz you need to
really get imaginative about modeling the parasitics, which include the
cabling *and* the environment (It's surprising the effect a shielded room
can have on your readings)
Note at the low end to be sure to include energetic magnetic fields, like
those from a wire supplying 20A spike through some such switching. Those
magnetic fields inject a lot of signal elsewhere.
Note also if you do anything active *ALWAYS* go back and test with a
sweeping generator and an SA. Look for out of bound fundamentals generating
inbound spurious tones. ...caught me off guard once. Never noticed the
effect using the tracking generator option, duh!
- Robert -
-----Original Message-----
From: Jim Eichner <jeich...@statpower.com>
To: 'EMC-PSTC - forum' <emc-p...@majordomo.ieee.org>
List-Post: emc-pstc@listserv.ieee.org
Date: Wednesday, September 15, 1999 10:09 PM
Subject: Re: Sweeping components and filters
>
>Thanks, Robert and Ed, for your replies. I have included them below,
>along with my original request.
>
>I'm guessing by the low number of responses, that not many people do
>this, which I guess isn't that surprising considering I too have been
>getting by without. Still, I'd appreciate any further input people
>have, particularly regarding methods that extend up into the 10's or
>100's of MHz.
>
>Ed's suggestion to use a sweeper with our SA is an interesting one. It
>hadn't occurred to me that I don't need to synch up the two instruments,
>but can just let the display fill in. If Ed or anyone else can add a
>catalogue number or two to the list of mfr's (Wiltron, Wavetek, and HP)
>that would save me reinventing the wheel. Also, Ed, is this method
>useable over a wide frequency range, into the 100-200 MHz neighbourhood?
>
>Robert: You say you sweep the components, then model the filter, then
>sweep the filter and compare to the simulation. How good is the
>correlation between the model and the network analyzer sweep? How good
>is the correlation between either and the real-life performance of the
>filter when you drop it into your noisy circuit?
>
>Finally, the idea of upgrading my SA to add in the tracking generator is
>still kicking around my head. Any input people have regarding the
>usefulness of the SA/TG combo for sweeping filters would be appreciated,
>along with any other things that people use the combo for.
>
>Thanks for your help,
>
>
>Jim Eichner
>> Senior Regulatory Compliance Engineer
>Statpower Technologies Corporation
>jeich...@statpower.com
>http://www.statpower.com
>> phone: (604) 420-4820 ext. 2162
>> fax: (604) 420-1591
>Any opinions expressed are those of my invisible friend, who really
>exists. Honest.
>
>
>-----Original Message-----
>From: owner-emc-p...@majordomo.ieee.org
>[mailto:owner-emc-p...@majordomo.ieee.org] On Behalf Of Price, Ed
>Sent: Friday, September 10 1999 02:21
>To: 'Jim Eichner'; 'EMC-PSTC - forum'
>Subject: RE: Sweeping components and filters
>
>Jim:
>
>OK, here's my 2 Euro's opinion!
>
>If you are starting from scratch, then buy a used HP-141T mainframe with
>an
>8552 and 8556 plug-ins. This will give you a spectrum analyzer with
>analog
>memory, covering 20Hz to 300 KHz. And it has a tracking generator to
>provide
>the excitation. Later you can buy some other plug-ins which will give
>you a
>pre-compliance tester for CE & RE. Here in the USA, you can get this for
>under $1000.
>
>OR
>
>If you have a spectrum analyzer with a memory, you can use a sweeper as
>the
>source. Wiltron and Wavetek and HP sweepers can be obtained on the
>surplus
>market for several hundred dollars. No need for any sync between the
>two.
>Set the sweep ranges for both, and let them run for a while until you
>fill
>in the spectrum of interest.
>
>You can kludge up other combos with sweepers and scopes/RF VTVM's etc,
>but I
>don't recommend it.
>
>Hey, why not do it all with software? I have a project (on very low
>priority) to use a PC's sound card as both an excitation source and a
>spectrum analyzer. I bought the Spectra Plus software for $300, then am
>using a Media Vision Pro sound card (also have a Turtle Beach Fiji with
>better S/N ratio) to generate a sweep and track/display the response.
>The
>only down-side to this is that you need to pad the output and input
>ports
>with 50 ohms (to duplicate the way OTHER filters are almost always
>tested).
>And, the frequency range is limited to about 30Hz to 22 KHz (because the
>sound cards sample at 44 KHz).
>
>Regards,
>
>Ed
>
>-----Original Message-----
>From: Robert Macy [SMTP:m...@california.com]
>Sent: Monday, September 13, 1999 2:09 PM
>To: Jim Eichner; 'EMC-PSTC - forum'
>Subject: Re: Sweeping components and filters
>
>I use that HP Network analyzer that goes to 500MHz. On a component by
>component basis. Then shove that all into a PSpice circuit which allows
>me
>to add parasitics, etc.
>
>Then I can play games with waveforms, risetimes, components, etc and
>pretty
>much predict what the filter will do.
>
>Sometimes as a confirmation, I'll then put the whole filter back into
>the
>network analyzer and see how it compares. Performance versus frequency.
>
>It is true that different noise sources inside the unit have different
>characteristic impedances and as with any filter, you need to match
>those
>impedances to what you're doing in order to maximize the performance of
>your
>filter.
>
>In otherwords, if this is a custom filter, make it match the
>requirement,
>don't make a generic one.
>
>
>-
>Robert -
>
>
>> -----Original Message-----
>> From: Jim Eichner [SMTP:jeich...@statpower.com]
>> Sent: Thursday, September 09, 1999 4:03 PM
>> To: 'EMC-PSTC - forum'
>> Subject: Sweeping components and filters
>>
>>
>> Greetings all:
>>
>> I have long wished that I had an instrument for sweeping filters and
>> components that I am working on, to determine where I can expect the
>> usefulness to start rolling off, where and if there are resonances,
>> etc.
>> Several options have crossed my mind, including adding a tracking
>> generator to my spectrum analyzer, buying an impedance analyzer, using
>> a
>> network analyzer, etc.
>>
>> I'd appreciate any experiences, advice, and recommendations the group
>> has to offer. I'm looking for input on cost, effectiveness, usable
>> frequency range, methods, issues like minimizing (or nulling?)
>> parasitics, effects of impedance mis-match (the instrument may be
>> 50ohms
>> but there's no way the circuit being filtered will be!), etc.
>>
>> I'll gladly collate the replies and send them back to the group once
>> the
>> discussion's done. Please reply to the forum, not to me directly, so
>> we
>> get some dialogue going.
>>
>> Thanks
>>
>> Jim Eichner
>> > Senior Regulatory Compliance Engineer
>> Statpower Technologies Corporation
>> jeich...@statpower.com
>> http://www.statpower.com
>> Any opinions expressed are those of my invisible friend, who really
>> exists. Honest.
>>
>>
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>
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