Difference between revisions of "FAQ/Emission"
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For a G-tem measurement you need to change the [[EUT]] to all three axis (X,Y and Z). During the measurement of one side you will see the emission coming out of that side. After measuring all three side the G-tem correction to the [[OATS]] can be applied, including the normalised site attenuation. For frequencies smaller then 1 Ghz this can mean that the total value is lower then the measured on one side. For example the attenuation for a horizontal 3 meter site at 30 MHz is 15.8. For the horizontal 10 meter site at 30 MHz this is 29.8. See the standard for the rest of the values. | For a G-tem measurement you need to change the [[EUT]] to all three axis (X,Y and Z). During the measurement of one side you will see the emission coming out of that side. After measuring all three side the G-tem correction to the [[OATS]] can be applied, including the normalised site attenuation. For frequencies smaller then 1 Ghz this can mean that the total value is lower then the measured on one side. For example the attenuation for a horizontal 3 meter site at 30 MHz is 15.8. For the horizontal 10 meter site at 30 MHz this is 29.8. See the standard for the rest of the values. | ||
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Revision as of 20:04, 21 January 2009
This page contains all the Frequently Asked Questions related to Radiated Emission and Conducted Emission module of RadiMation®
How does a G-TEM compare to an anechoic chamber?
A G-TEM cell is in principle not an accepted (full compliant) EMC test environment and compared to an anechoic chamber the cables will be routed and placed differently.
Sometimes the error at higher frequencies becomes smaller through the band. This is what normally is expected in case of correlation measurements between a small G-TEM in relation to a large Anechoic chamber or OATS (due to near field effects smaller test rooms will have larger deviations at low frequencies).
Beside this, one should realize that even full compliant radiated emission measurements still have relatively high measurement uncertainties. To give you some concrete figures:
- The absolute accuracy for an OATS measurement (including all uncertainties of equipment, site attenuation and antenna factor) are about +/- 5 dB.
- For emission measurements in anechoic chambers this figure is about +/- 6 dB for a SAR and even +/- 10 to 20 dB for a FAR.
So one can imagine that you can expect even higher uncertainties in a (G)TEM cell
Generally when comparing two sites with each other it is important to make the correct calculations for both uncertainties (root sum of the squares). So if both sites have 5 dB uncertainty (which is not feasible with a TEM cell) the total expected difference will be maximum 7 dB. In other words a measured 10 dB difference is not even bad at all!
Auto attenuator is going to 10 dB even with low emission values
When auto attenuation is selected, RadiMation® sends a command to the receiver or analyser to select auto attenuation. The attenuation that will be selected by the receiver or analyser is then depending on the used measurement device itself. When an analyser is used, it can help to decrease the reference level to for example 50 dbuV. Verify if the attenuator has been decreased at the lower reference level setting. A lot of analysers can only use a 0 dB attenuation value, if the reference level is lower or equal to -20 dbm (or 87 dBuV).
Why is there a big drop between the value during and after a G-tem measurement?
For a G-tem measurement you need to change the EUT to all three axis (X,Y and Z). During the measurement of one side you will see the emission coming out of that side. After measuring all three side the G-tem correction to the OATS can be applied, including the normalised site attenuation. For frequencies smaller then 1 Ghz this can mean that the total value is lower then the measured on one side. For example the attenuation for a horizontal 3 meter site at 30 MHz is 15.8. For the horizontal 10 meter site at 30 MHz this is 29.8. See the standard for the rest of the values.
