Electric Field strength to power conversion.. - RF Cafe Forums

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bparker

Post subject: Electric Field strength to power conversion..

Posted: Tue Apr 12, 2005 8:01 am

Lieutenant

Joined: Fri Aug 27, 2004 11:25 am

Posts: 4

Location: Cape Town, R.S.A.

Hi All,

I was hoping someone could help me with a fundamental issue.

I have had some EMC problems (radiated) and am trying to analyse the results.

The test is done by monitoring the radiated signal with an antenna placed 1m from the DUT. The levels are then given in dBuV/m.

I understand that this is a measure of the Electric field strength, but my question is how to relate this to an absolute power measurement.

Is it a straight conversion from dBuV to dBm, assuming a 50 ohm system, and can the /m part of the unit be dropped because of the distance between DUT and antenna being 1m?

If this reasoning was followed, a +30dBuV/m translates to -77dBm/m, or -7dBm power level at source if a cable with 70dB isolation was used. (cable connected to known source of offending signal and terminated into 50 ohm)

Am I way off the mark, and if so can someone please shed some light?

_________________

B.K.P.

RMYREHN

Post subject: Electric Field strength to power conversion..

Posted: Tue May 10, 2005 10:13 am

To convert from dBuV to dBm in a 50 ohm system, just subtract 107 from the value in dBuV. As far as dropping the /m (per meter), you will need to obtain the antenna correction factor (which should have been supplied with the antenna) and subtract it from the value. Once you have this answer, it is no longer a field strength though. This is useful if you want to determine what level to inject (bypassing the antenna) when checking out your measurement system

Posted 11/12/2012

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