Re: RJ-45 common mode radiated emissions testing
Thanks for the reply and thanks for the testing. I certainly am not
requiring you to undertake additional work.
Its just that reflections for open (unterminated) wires is at least
double giving 6 dB more radiation. And resonances will make it worse.
The TIA found serious resonances due to short patch cords without proper
terminations. I have found resonances with common mode chokes (big ones,
in the order of half a mH) as low as 50 KHz.
Rick Brooks wrote:
> I was trying for the worst case for common mode radiation.
> There were not any differential mode signals generated, except by mode
> The results are ball park in any case.
> What you ask for is possible, but not what I was trying to do.
> I wanted to add one data point for what common mode noise could be
> tolerated from the PSE power supply,
> given Roger's conclusion that radiated emission requirements are the
> more restrictive limit for power supply noise.
> A conclusion that I agree, by the way, with for frequencies of 30 MHz
> and higher.
> I did this EMC testing as a freebie, I don't have a plan to redo this
> EMC testing.
> If I do any testing in the future, I will keep your request in mind.
> - Rick
> -----Original Message-----
> From: Jack Andresen [SMTP:jandresen@xxxxxxxxxx]
> Sent: Friday, September 15, 2000 1:55 PM
> To: Brooks, Rick [SC5:321:EXCH]
> Cc: stds-802-3-pwrviamdi@xxxxxxxx
> Subject: Re: RJ-45 common mode radiated emissions testing
> The data helps. However, is it possible to redo with proper
> on the end of the cable. You need both differential and common
> terminations. Unterminated end reflections will increase mode
> Jack Andresen
> Rick Brooks wrote:
> > I have posted the test setup and results of a radiated
> emissions test
> > that I did recently in a 10 meter anechoic chamber.
> > The test was to try to determine what common mode signal
> voltage would
> > produce a radiated field that would be at the
> > compliance limit, class B in this case.
> > I hope that this data will help us to specify a noise
> requirement for
> > the DTE power from the PSE, as well as the PD.
> > It is important to understand that the radiated emissions
> > only cover from 30MHz and higher.
> > The spectral region from 500 kHz to 30 MHz, is obviously of
> > to 10/100/1000, but I don't cover it here.
> > The pdf file is at:
> > comments, questions?
> > thanks,
> > - Rick