|
Fig.2-11 block diagram of a test setup for open-area measurements. Make sure that the antenna Is decoupled from the printer and plotterSetting of the Test ReceiveAn automatic test run can only be recommended for the measurement in the shield room, e.g. as prescan for rough determination of the field strength and the interference frequencies with subsequent testing at single frequencies in open-area measurements。A test configuration does not have to be determined. Before starting the scan , it is advisable to adjust the antenna and the EUT to the maximum level display at the frequency with the highest interference field strength (e.g. at the switching frequency of a switching power supply or at the line frequency of a monitor). The scan setting determines the prescan. The setting data recommended in the section “Measuring the RIF Field Strength in the Frequency Range up to 30 MHZ”are also valid in this case. Pk is to be used as detector since only one QP limit value exists. Test run methods of measurement and analysis What has been said in section “Measuring the RIF Field Strength in the Frequency Range up to 30 MHZ”also applies to RFI field-strength measurements, of course without the phase selection . Measuring the RIF Field Strength in the Frequency Range above 30 MHZ In the frequency range from 30 to 1000 MHz, RFI field-strength measurements are in most casea performed at open-area test sites at a distance of 3, 10 or 30 m from the EUT. Linearly polarized broadband dipoles serve as antennas for horizontal and vertical polarization. In general, two antennas are used , e,g, a HK116 (30….300MHz) and a HL 223 (200….1000MHz) or a HUF-Z1(30…80MHz)and a HL 023 A1 (80…1000MHz). The field-strength test sites feature a conductive ground plane and must comply with a test-site attenuation characterized by a strict tolerance. Therefore, there are only few proper test sits in shielded (anechoic) chambers, since the required facilities are very expensive. Due to the conductive ground plane, the field strength does not only depend on the polarization. But also the height. The antenna must therefore be shifted in height in a range from 1 to 4 m. since the EUT itself also features an emission depending on the direction, it is to be rotated and operated in various operating modes and cable configurations, if applicable. A considerable problem is caused by ambient interference present on open-area test sites, which is often intermittent, I.e. not constant with respect to time. For these reasons, it is not advisable to perform a fully automatic test run without the aid of a computer with a test receiver. The ESCS therefore offers the following solution: In a not quite ideal anechoic chamber , a prescan is performed without height variation of the antenna (e.g. in the short-range field at a distance of 1 m form the EUT) for searching the maxima. The frequencies are stored in the ESCS for subsequent manual open-area measurements. If there is a ground reflector (semi-anechoic) the optimal height may have to be set. Test setup for RFI field-strength measurementThe shielded room contains the EUT and the antenna, whereas the test receiver and the peripheral equipment are located outside. The test configuration of the EUT including all connected lines should be identical with that used in the open-area measurement. The antenna should possibly be located in the main direction of emission of the EUTIt is recommended to use an antenna setting below 45 degrees for the prescan (i.e. neither horizontal nor vertical ). Therefore ,one scan is sufficient. |
